260 JouRul oF THE ArrlpnrclN Mosquno CoNrRor, AssocrarroN Vor. . 7 , No.2

PERSPECTIVES ON MANAGEMENT OF PESTIFEROUSCHIRONOMIDAE (DIPTERA), AN EMERGING GLOBAL PROBLEM

ARSHAD ALI

Uniuersity of Florida, IFAS, Central Florida Research and Education Center, 2700 East Celery Auenue.Sanford, FL 32771-9608

ABSTRACT. In recent years, adult Chironomidae emerging from some urban natural or man-madehabllats have increasingly posed a variety of nuisance and economic problems, and in some situationsmedical problems to humans in different parts of the world. Although there are an estimated 4,000 ormore species of chironomid midges worldwide, less than 100 species have been reported to be pesti'ferous.Among midge control methods, numerous laboratory and field studies have been conducted on the useof o^rqanochlorines, organophosphates (OPs), pyrethroids and insect growth regulators (IGRs). Field useof OP insecticides such as chlorpyrifos, temephos and others in the USA ind Japan hai generallyresulted in larval control for 2-5 wk or longeiwith application rates below 0.56 kg AI/ha (U=S.q) ani51-5 ppln (Japan). Frequent use of some OP insecticides in the USA and Japan has caused.theirincreased tolerance in several midge species. The IGRs, diflubenzuron and methoprene, provide alternatemeans for midge control. These IGRs in some situations suppressed adult midge eme.ge.tce by >g\Vo atrates (0.3 t<g ll/_hqr A number ofparasites and pathogens have been reported from mldges in differentparts of the woid'. Bacillus thuringiensis serovar. israelensis is effective igainst some mid-ge species, butat rates at least 10x or higher established for mosquito larvicidal aciiuity. The flatriorm, Dugesiadoro.tocephala, and some fish species offer a good potential for midge control in some situations. In l"argehabitatscovering hundreds or thousands of ha, information on t[e basic ecology of larval midges aridadult behavior is essential for formulating midge control criteria. More reseirch is neededln thebiological and physical and cultural control of these pestiferous insects.

INTRODUCTION

Nonbiting midge flies of the dipteran familyChironomidae commonly occur in most inlandnatural or man-made aquatic ecosystems of di-verse natures. They inhabit shallow and fastflowing headwaters of streams and rivers as wellas deep and slow moving waters in lagoons.Midges occur in stagnant waters in small andshallow temporary or permanent ditches andponds and in large shallow or deep lakes. Chi-ronomid larvae exhibit a very wide range oftolerance to environmental conditions as indi-cated by their presence in "clean" waters satu-rated with dissolved oxygen, as well as in "pol-

luted" waters very low in oxygen. The occur-rence of certain species of midges in pollutedwaters is indicative of the type of pollution intheir habitat. Due to their adaptive nature, somemidge species survive even in brackish, estuarineor marine environments. Although most chiron-omids are aquatic, a few species occur in decay-ing organic matter, under bark, or in moist soil.

In recent years, large populations of midgelarvae have been reported in different countries(e.g., USA, Japan, Italy, Sudan and others).Some central Florida lakes support midge larvaldensities of 10,000-40,000/m'� or higher, result-ing in heavy emergence of adult midges fromthese lakes (AIi and Baggs 1982, Callahan andMorris 1987, Patterson 1964). Similar larvaldensities of midges are encountered in somerivers and lakes of Japan (Moriya 1977, Ohnoand Shimizu 1982, Tabaru 1975. Tabaru et al.

1978), in the lagoon surrounding the city ofVenice, Italy (AIi et al. 1985b), in man-madeurban and suburban aquatic environments, suchas shallow and open wastewater channels (Aliand Mulla 1976a), water spreading basins (Aliand Mulla 1978a), sewage oxidation and settlingponds and overflow gutters (Edwards et al. 1964,Spiller 1965,Tabaru 1985b), and residential-rec-reational lakes (Ali and Mulla 1977b, Ali et al.1978).

Generally, water bodies in urban and subur-ban areas exposed to intensive human use (res-idential, recreational, agricultural, etc.) and alsoreceiving discharges from point and nonpointsources are becoming increasingly eutrophic. Asa consequence, macrofaunal species diversity inthese habitats is gradually decreasing and re-sults in the survival and profuse breeding ofmore pollution-tolerant organisms, such as somespecies of Chironomidae that constitute a majorcomponent of the macroinvertebrates. It shouldbe understood that generally chironomid larvaeplay a beneficial role as an important source offood for the predatory fish and some other in-vertebrates in the food web of aquatic ecosys-tems. The larvae also keep the aquatic environ-ment clean by consuming and recycling organicdebris; hence, they are considered highly desir-able organisms in the ecosystem. However, theadult midges from some densely populated hab-itats frequently emerge in large numbers, caus-ing a variety of nuisance, economic and in somesituations medical problems for humans residingor working near their breeding sources. The ever

JUNE 1991 MeNecnupNt or PosrlrnRous CnrRoNolrroen

increasing importance of chironomids as a pestand the somewhat scattered literature on theirchemical, biological, physical and cultural con-trol necessitated compilation of this review.

NUISANCE, ECONOMIC ANDMEDICAL PROBLEMS

Dense swarms of midges often limit outdoorhuman activity since the adults can be inhaledor fly into the mouth, eyes and ears of an indi-vidual. They are liable to cause asphyxia incattle. During summer, midges seek cool andshady places in the daytime leaving behindstained stucco, paint and other wall finishes onwhich they rest. They also soil automobiles, andcover the headlights and windshields, causingtraffic accidents. At night, the adults are at-tracted to light, swarming around indoor andoutdoor fixtures. Adults of some small-sized spe-cies pass through standard screens on doors andwindows and thus create nuisance and economicproblems indoors, such as staining laundry,walls, ceilings, draperies and other furnishingsas well as causing discomfort for the residents.Adult midges cause a considerable economic lossto the hotel and tourism industry (Ali 1980b).Accumulations of dead midges and the unsightlyspider webs in which midges are trapped requirefrequent washing and maintenance of proper-ties. They clog automobile radiators and air-conditioning wall units and are a problem forsome paint, pharmaceutical and food processingindustries where hordes of adults fly into thefinal products. The dead midges produce anunpleasant odor similar to rotting fish. Thisodor persists in damp weather for several days,even afber the adults have been removed. Attimes, the dead adults accumulate on roads insuch quantities that they make the roads slip-pery, causing traffrc hazards. At the Marco PoloAirport near Venice, Italy, there is a great con-cern for the potential of airplanes skidding overmassive accumulations of dead midges on therunways, and also, of economic loss due to theadults flying into delicate equipment (gauges)mounted on the planes (E. Tsuroplis, personalcommunication). Midge swarms pose severe nui-sance problems to passengers and crews ofcargovessels and other boats moving through the la-goon of Venice, thus adversely affecting humanactivity in that historically touristic area.

Adult midges are not vectors of any diseaseorganism although they are considered to bemechanical carriers of some microorganismswhen emerging from polluted waters (Lysenko1957, Steinhaus and Brinley 1957). They are,however, associated with human allergic reac-tions such as asthma and rhinitis in Africa

(Cranston et al. 1981, Gad-El-Rab and Kay1980), Europe (Giacomin and Tassi 1988) andAsia (Ito et al. 1986). It is believed that midgesare a potential cause of allergies worldwide(Cranston et al. 1983). Adult midges may evencause anaphylactic shock in some individuals(M. Sasa, personal communication).

Chironomid larvae, too, can produce certainundesirable effects. When inhabiting storageand distribution systems for potable water, lar-vae may pass through taps causing concern tohouseholders. There are numerous reports ofmidges infesting water systems in various partsof the world (e.9., Hafrz 1939, Flentje 1945a,Wilhelmi 1925, Williams 1974). Larvae of sev-eral midge species also have been implicated asagricultural pests. For example, there are severalreports of damage to rice seeds and plants bychironomid larvae (Darby 1962, Ishihara 1972,Risbec 1951); members of the subfamily Ortho-cladiinae injure roots of Japanese horseradish(Yokogi and Ueno 1971); and Stenochironomusnelumbus feeds on floating leaves of lotus (Nel-umbo wcifera) (Tokunaga and Kuroda 1936).

PREDOMINANT NUISANCE SPECIES

There are probably more than 2,500 speciesof Chironomidae in North America (Coffmanand Ferrington 1984). It is estimated that thereare 4,000 or more species of midges worldwide(A. Soponis, personal communication). A sum-mary of ecological and distributional data onChironomidae was given by Coffman and Fer-rington (1984). Of the 7 subfamilies of Chiron-omidae, species most commonly encountered inheavy midge producing urban and suburbanhabitats are in the genera Chirornmus, Crypto-chironnrnus, Goeldichironomw, Glyptotendipes,D ic rotendipe s, P aralnuterbo rniella, P olypedilum,Tanytarsus, Cla.dotanytarsus, Rheotanytarsus,Tokunagayusurika, Cricotopus, Proclad,ius, Coe-latanypus, Tanypus and Pentaneura. Species oIa few other quantitatively less important generamay also occur in some locations.

In general, Chironomus deconts, C. frommeri,Dicrotendipes californicus, Cricotopus bicinctus,C. syluestris, Procladius freemani and a few spe-cies of Tanytarsus are most widely distributedin California and are potentially pestiferous (Aliand Mulla 1979b). Specifically, in 1-2 m deepman-made lakes, water spreading basins andflood control channels in southern California,Tanytarstn, Chironornus and, Procladius aremost common (Ali and Mulla 1975, 1976b; AIiet al. 1978), while Cricotopus predominates instorm drains (Ali and Mulla 1979c, Ali et al.1977). In 2-4 m deep recreational lakes in Cali-fornia, Chironomtts and Procla.dius are most

JouRNer, oF rHE AupRrceN Mosqurro CowrRor, AssocrnrroN Vor.. 7, No. 2

abundant and emerge at nuisance levels (Ali andMulla 1977b, Mulla et al. 1925, 1926). The spe-cies composition of adult midges in some south-ern California problem situations was compiledby Grodhaus (1968) and AIi and Mulla (19?9b).

In Florida, Glyptotendipes paripes, Chirono-mus crassicaudatus and. C. decorus are the maiorpest species of midges (Ali and Baggs 1982, iliand Fowler 1985). Beck and Beck (1969) alsoprovided a list of nuisance species of chironom-ids in Florida. In Illinois, ihirono*us ripariuscauses annoyance (Polls et al. 19Zb). C. decoruswas a problem in New York (Jamnback 19b6)andC. plumosus in Wisconsin (Hilsenhoff 1g5g).There may be several more unreported pestifer-ous species of chironomids in the United States.Outside of the United States in recent years,Cladotanytarsus lewisi in Sudan (Cranston et al.l98l), Chironomus salinarlus in Italy (Ali et al.1985b), and Tokunagayusurika akamusi, Chiron-omus yoshimatsui and C. plumosus in Japan(Tabaru et al. 1987) have been reported to bepestiferous and/or a cause of allergies.

Identification of larval and adult chironomidsto the species level is somewhat difficult due tothe lack of proper taxonomic keys; however,generic identification is feasible under most cir-cumstances. In combination, the keys providedby Beck and Beck (1969), Coffman and Ferring-ton (1984), Darby (1962), Mason (1973), Oliveret al. (1978), Roback (1971), Sublette (1960,1964), Sublette and Sublette (1971) and Wirthand Stone (1956) are useful. For taxonomic pur-poses and other laboratory investigations, somemidge species can be reared and/or colonized byusing the techniques ofBiever (1965, 1971).

CONTROL METIIODS

A variety of control methods have been inves-tigated in the past several decades. Most ofthesestudies were focused on chemical control. Somework has been conducted on biological controlof this pest through the use of predators. Anumber of parasites and pathogens have beenreported from midges, but very few of thesemicrobial organisms have been subjected tomass culturing and inoculation of natural breed-ing sources, or studied in a quantitative manner.Physical and cultural control methodologies ofchironomids also remain the least explored.

In some situations, satisfactory but temporarycontrol of chironomids may be achieved by em-ploying physical and cultural, biological orchemical means, depending upon the nature ofthe breeding source. Usually, in small habitats(<200 ha) one or more control techniques areeffective. However, an integrated approach com-bining the various control methodologies is de-

sirable and should produce better results. InIakes and lagoons covering several thousand ha,such as in central Florida or around Venice,Italy, midge control by the use of insecticides asIarvicides is not economically feasible becauseof the large volumes of water to be treated.Chemical displacement, adverse effects onaquatic nontarget organisms and other environ-mental concerns also severely restrict or preventthe use of insecticides as larvicides. In suchhabitats, an understanding of the ecology andmanipulation of the larval environment andthe adult behavior, combined with the use of nat-ural enemies, may provide some solution to theproblem.

Physical and cultural: Midge control methodsthrough environmental management are poorlydeveloped, primarily because a precise under-standing of the ecological bases for midge pro-duction in various problem habitats is lacking.Among the methods used to reduce larval den-sities, the mechanical removal of sludge and eggmasses of chironomids from the sides of rivers,and disturbing the riverbeds by dredging andmixing the substrate materials (Shimizu 1978)were ineffective in producing control. In semi-permanent habitats, such as water spreadingbasins, some reductions in midge populationsmay be achieved by rotational flooding anddrying of partial areas of breeding sources (An-derson et al. 1964). However, more frequentdrying, dredging and reflooding of such habitatsmay be conducive to higher midge productivityand midge nuisance problems (Ali and Mulla1978a). Increase in depth of some temporary orpermanent habitats also reduced some midgepopulations (Ali and Mulla 1976c). In concrete-lined storm drains, removal of substrate mate-rials by mechanical means, or by natural factorssuch as rainfall, reduced populations of midgelarvae (Ali et al. 1976b, 1977). Proper designingof reservoirs and lakes in some situations wouldbe helpful in keeping midge populations at lowerIevels (Magy 1968). Information related to nu-trient cycles and availability, and the influenceof nutrients on primary and secondary produc-tivity, which in turn have an impact on theabundance of nuisance chironomids in someman-made habitats, is desirable (Johnson andMulla 1984). Understanding the role of macro-phytes as physical barriers or as sources of re-lease of biologically active chemicals that inter-fere with midge survival and development insome habitats is useful for the ecological manip-ulation of midge production (Johnson and Mulla1982b. 1983).

Exploration of midge control by physical andcultural control techniques is highly desirable inhuge breeding sources, such as the lakes in cen-

JUNE MANAGEMENT OF PESTIFEROUS CHIRONOMIDAE 263

tral Florida and the lagoon of Venice, Italy. Insuch situations, knowledge of the physicochem-ical environment of the nuisance species, i.e.,the physical and chemical composition of thesubstrate materials and chemistry of the over-Iying water in relation to the spatial and sea-sonal abundance and distribution of larvae ofthe pest species, may provide a clue to theirecological basis of production. Their prolifera-tion could then be discouraged by manipulatingthe nutrients (pollutants) and/or other factorsconducive to their breeding and rapid propaga-tion. Recently, chemistry of sediments, waterchemistry and midge populations in a centralFlorida lake, Lake Monroe, were monitored byAIi (1989). These studies revealed that larvaldensities of G. paripes and C. crassicaud,atuswere inversely related with water depth, andthat populations of the former species were in-versely associated with total phosphorus (TP),Kjeldahl nitrogen (kj-N), organic carbon andsome micronutrients while the latter species wasdistributed irrespective of the concentrations ofthese chemical parameters.

Thus, environmental requirements of midgespecies may differ from species to species. BothG. paripes and C. crassicaud,atus, however,showed significant (0.01 level) positive correla-tions with electrical conductivity, concentra-tions of chlorophyll o, and the standing crop ofCyanobacteria (:"blue-green algae") and totalphytoplankton. Since larvae of C. crassicaudatus(Ali 1990) and G. paripes (Provost and Branch1959) feed on phytoplankton, particularly Cy-anobacteria, and the abundance ofthese speciesis directly related to the phytoplankton abun-dance, it was concluded that the occurrence ofhigh densities of C. crassicaudatus and, G. paripeswas a function of phytoplankton abundance inwater. However, many other interrelated biolog-ical and chemical parameters may also playsome role in the population fluctuations of thesemidges. Since Lake Monroe is a part of the St.Johns River system, it may be possible to arti-ficially increase the water flow through the lakeat times of midge larval abundance to displacephytoplankton populations and, in turn, reducemidge densities. Thus, it appears that in someIarge habitats, physical and cultural control ofmidges may be practical through knowledge ofthe basic ecology of the nuisance species. Theecology should be investigated in habitats suchas the lagoon of Venice and in other locationsbecause each habitat possesses its own charac-teristics in terms of midge and other inverte-brate fauna. Information gathered in one habitatmay not be applicable to another with similarproblems.

Another possibility of cultural control ofmidges is through the understanding and manip-ulation of their adult behavior. For example,studies in the laboratory (Ali et al. 1984) andfield (AIi et al. 1986) in central Florida on theattraction of G. paripes, C. crassicaudatus, G.holoprasinus, P. halterale and other species re-vealed that among a combination of white (in-candescent and fluorescent), yellow, orange,blue, green and red lamps of the same wattage,these species were generally attracted the mostto white light (highest intensity) and the leastto blue, green or red light (lowest intensity).This behavior of adult midges is in contrast toadult mosquito behavior; a majority of mosqui-toes respond to a specific color or wavelength inthe electromagnetic spectrum (Ali et al. 1989b),while midge species respond more to the quan-tity (power or intensity) of light (AIi et al. 1984).Such information is of practical significance incontrolling midges. Fifty or so species of chiron-omids and 3 of Chaoborus were collectively re-sponsible for the "lakefly nuisance" at Entebbe,Uganda; this nuisance was being ameliorated in1962 by the use of UV mercury-vapor lampsfaced away from occupied buildings, combinedwith window-screening, the elimination ofhedges in the lakeward side of dwellings, andthe planting of hedges on the Iandward side todirect the flies beyond houses and their gardens(M. Laird, personal communication). Many hab-itats producing midges at nuisance Ievels inFlorida, Italy (Venice lagoon) and perhaps else-where are surrounded by a high density of homesand businesses interspersed with less denselyinhabited areas. If dimmer lights could be usedin the densely inhabited areas and high intensity(brighter) lights installed in and around the lessdensely inhabited areas, adult midges would bedrawn to the latter areas where suitable controlmeasures could be implemented. Along the Iinesof midge adult behavioral studies for controlpurpose, information on adult dispersal (AIi andFowler 1983), patterns of abundance (Ali et al.1983, 1985a) and diel eclosion periodicity (AIi1980a, Ali and Mulla 1979a, Ferrarese and Cer-etti 1989) should be useful in reducing the costof adulticiding. Applications of insecticidescould be synchronized with the emergence ofadults, thereby reducing the area to be treatedand the amount of material needed.

In some situations, relief from adult midges isachieved by using electrocutor traps. However,the attraction of huge numbers of adults in mostsituations cause the traps to malfunction astheir body fragments stick and completely coverthe grid in the trap. Intensive research is pres-ently being conducted to improve the efficiency

JouRrulr, oF THE AMERTCAN Mosqurro CourRor. Assocrlrtox VoL. 7, No. 2

of electrocutor traps for midge control (W. Ad-kins, personal communication).

Binlngical: parasites and pathogens.. Manybiotic control agents regulate populations of chi -ronomids in nature. Viruses, rickettsiae, proto-zoans, nematodes and fungi have been reportedin the literature.

Among aquatic insects, only chironomidmidges are reported to be hosts of entomopox-viruses (Anthony 1975). Weiser (1969), Hlgeret al. (1970), Stoltz and Summers (1921), Fed-erici et al. (1974), Harkrider and Hall (1975)and Majori et al. (1986) have reported entomo-poxviruses in Camptochironomu,s tentans, Chi-ronomus luridus, C. attenuatus (a junior syn-onym of C. decorus) and C. plumosus, Goel.di-chironomus holoprasinus, C. decorus and C.s alinar ius, respectively.

Entomopoxviruses have been shown to play asignificant role in the natural regulation of nui-sance midge populations (Harkrider and Hall1978). In laboratory studies, Harkrider and Hall(1979) demonstrated the important role of highmidge population density in the precipitation-ofan epizootic of entomopoxvirus. However, thereported larval mortalities of field populationsof chironomid species infected by poxviruses indifferent habitats range from <1 to 100% (An-thony 1975, Huger et al. 1g70, Majori et al. 1986,Weiser 1948). In addition to the poxviruses, acytoplasmic polyhedrosis virus (CPV) in chiron-omids collected from Florida was detected bvFederici et al. (1973), and another virus closelvrelated to iridoviruses was found in C. plumosusin Wisconsin (Stoltz et al. 1968).

Among fungi, the genus Coel,ornomyces is apathogen of chironomids. Rasin (1929) reportedCoelomomyces chironomi in midge larvae. Later,this fungus was also found in C. paraplumosusin Czechoslovakia (Weiser 1g76, Weiser aniV6vra 1964). Weiser and McCauley (1971) dis.covered 2 Coelomomyces infections of Chiron-omidae in Marion Lake, British Columbia. Can-ada, but their C. beirnei is now "highly suspect,'as a member of this genus and thought to be aprotozoan (Couch and Bland 198b). The sameauthors also reported a new fungal species, Ber-tramia marionensis, parasitizing midge larvae(Weiser and McCauley 7974).

The occurrence of rickettsiae in midges is rare.Richettsiella chironomi in C. decorus (G otz lg7 2)and a Richettsi.ella-llke organism in C. frornmeri(Federici et al. 1976) have been reported.

The protozoan parasites of midge larvae arerepresented by microsporidia and ciliophores.Weiser (1961) discovered 16 species of micros-poridia in chironomids. Hilsenhoff and Lovett(1966) found Th.elohania in a chironomid inLake Winnebago, WI. They reported that the

incidence of disease ranged from 0.g to g.1Vo inflreld populations with no viable adults maturingfrom the infected larvae. This a$eed with anearlier report of Weiser (1963).

-Microsporidia

can play an important role in the regulation ofaquatic insect populations. A good example ofthe potential value of microsporidian infectionis the annihilation of midges in B semiperma-nent ponds 3 wk after initial detection of thediseased larvae (Hunter 1968).

Most reports of ciliates parasitizing insectsconcern the genus Tetrahymena. The system-atics and parasitism of this genus was reviewedby Corliss (1960), who reported a fatal attack ofT. chironomi and ?. pyriforrnis on C. pluntosus.These ciliates were found in up to lL8% of C.plumosus larvae in 8 samples and the incidencewas greater in larger larvae; 43.2Vo ofthird instarlarvae in one sample were parasitized. Bar-thelmes (1960) found another species, T. para-sitica, in C. plumosus. However, no epizootics ofciliates controlling midge populations have beenreportect.

A number of nematode parasites of midgelarvae have been reported in the literature (e.g.,Gotz 1964, Karanukaran 1966, McCaulev 19Zd).Johnson (1963, 1965) reported Octornyornermisitascensis in C. plum.osus and, Hydromerrnis itos-censis in Glyptotendipes lobiferus in the centralUnited States. Parenti (1966) found paramer-mis contorta in C. tentans in France. Poinar(1964) reported a new nematode, Orthomermisoedobranchus, parasitizing Srnittia sp. larvae inEngland, a new species of Gastromernzrs parasi-tizing Tanytarsus larvae in California (Poinarand Ecke 1967), and another mermithid. I/y-dromermis conophaga, in Tanytarsus larvae inCalifornia (Poinar 1968). There are severalother reports indicating that many mermithidshave a variety of host chironomids in variousparts of the world (Lewis 1.957, McCauley 1gT3,Wtilker 1958, 1961, 1963, 1965; Welch andPoinar 1965). Welch and Poinar (196b), Poinar(1981) and Petersen (1985) have discussed therole and use of nematodes in the regulation andcontrol of insects of medical importance.

In the USA, a monthly infection mte of Hy-dromermis contorta in C. plumosus ranged from0 to 24.8% throughout the year (Johnson 19bb1),while in Germany, natural mermithid infectionsin Tanytarsus midges at certain times of theyear were as high as l00Vo (Wiilker 1958, 1961).More recent investigations concerning mermi-

'Johnson, A. A. 1955. Life history studies on liy-drornermis contorta (Kohn), a nematode parasite ofChirornmus plun'Losus (L.). Ph.D. thesis, Univ. Illinois.Urbana.

JUNE MnNe,cuNrnxr op Prsrlppnous Cnlnoxolr.ttone 265

thids of chironomids are those of Chapman andEcke (1969) in percolation ponds in California,where the incidence of H. conophogo infectionin Tanytarsus reached 45% in a spring season.The authors concluded that the parasite con-trolled the midge populations for nearly 2 yearsafter the ponds were first flooded. Such inci-dences, however, are rarely observed in nature.

Two microbial agents, Bacillus thuringiensisserovar. israelensis (B.t.i.) and Bacillw sphaeri-cus, have great larvicidal potential against someDiptera of medical importance (Ali and Nayar1986, Ali et al. 1981, 1989a; Lacey et al. 1984,Mulla et al. 1982, 1988). Of the 2 spore-formingbacteria, different B.t.i. formulations are cur-rently being used as larvicide of mosquitoes andblackflies in various parts of the world (Kurtaket al. 1987, Majori et al. 1987, Merritt et al. 1989'Mulla et al. 1985, World Health Organization1982). Bacillus sphaericus, shown to be highlyeffective primarily against Culer mosquitoes (AIiand Nayar 1986, Ali et al. 1989a, Mulla et al.1988, World Health Organization 1985), is pres-ently being investigated and developed for com-mercial use in mosquito control programs. Thepotential for the 2 biocides in chironomid con-trol has also been investigated (Ali 1981a, AIiand Majori 1984, Ali and Nayar 1986, Ali et al.1981, 1985b; Rodcharoen et al. 1991). In labo-ratory bioassays, the LCgo values of G. paripes,C. crassicaudatus, C. decorus and Tanytarsusmidges ranged from 4.56 to 47.02 ppm withdifferent wettable powders (WP) and a flowableconcentrate (FC) of B.t i., including IPS-78(WP), R-153-78 (WP), ABG-6108 (WP) andSAN-402-WDC (FC), which had potencies of1,000-3,500 international units of toxicity(ITU)/mg (AIi et al. 1981). The same formula-tions of B.t.i. against Aedes aegypti and CuLexquinquefasciafus larvae were highly active (LCgo: 0.13-0.88 ppm), revealing that chironomidmidges, in general, are relatively less susceptibleto B.t.i. than mosquitoes. In other laboratorystudies (Ali and Majori 1984, AIi et al. 1985b),Bactimos@ (WP), Vectobac@ (WP) and Teknar@(FC) containing 1,500-3,500 ITU/mg testedagainst C. salinarius were shown to have LCsovalues ranged between 5.07 and 38.26 ppm.These results were comparable to those of Ali etal. (1981).

Field tests were conducted in experimentalponds (each 24 m2 at surface and 0.5 m deep)and in a golf course pond (1 ha at surface and0.6 m deep) in Florida with a WP formulationof B.t.i., ABG-6108, containing 1,000 ITU/mg(Al i 1981a). At t ,2 ,3, 4 and 10 kglha, ABG-6108 gave 18-88% Iarval reductions of Chiron-omini and Tanytarsini midges in the experimen-tal ponds. As expected, the highest rate of ap-

plication (10 kglha or 2.5 ppm) gave the highestIevel of control (E8%) after 2 wk of treatment.In the golf course pond, the rate of 3 kg/ha (0.5ppm) yielded 30-677o reduction of Chironomini,but Tanypodinae midges remained generally un-affected.

More recently, Rodcharoen et al. (1991) con-ducted a number of field studies with B.t i. formidge control in California. In ponds (each 30m2 at surface and 0.3 m deep), Vectobac'"'6A3(aqueous suspension containing 600 ITU/mg) atrates of 11.2 and 22.4kglha,yielded a maximumof 37 and 57% rcduction, respectively, of C.decorus, C. fuluipillus and. Paralauterborniellaelarhistus midges during the 2-wk evaluationperiod. In 3 separate man-made lakes (Wood-ward Lake, Woodbridge North Lake and LakeCalabasas), ranging from 8.4 to 21.6 ha at sur-face and 1.8 to 2.1 m in depth, different formu-lations of B.t.i. at various rates were evaluatedagainst midges. In Woodward Lake, ABG-6253(corngrit gtanules containing 200 ITU/mg) wasevaluated at rates of 13.5, 28 and 56 kg/ha in1.4- to 2-ha separate sections (fingers) of thelake. These rates yielded 22, 83 and 9670 conttol,respectively, of C. decorus midges at 2 wk post-treatment. Species of Tanypodin ae (Procladiusrnaculatus and Tanypus grodhausi) remainedunaffected. In Woodbridge North Lake, a tech-nical powder (TP) of B.t.i., ABG-6164 (contain-ing 12,430 ITU/mg), was tested at rates of 1.4and 2.8 kg/ha. These treatments yielded 73 and877o conftol, respectively, of Chironomus sp. at2-3 wk posttreatment. In Lake Calabasas, Vec-tobac'D TP containing 5,000 ITU/mg was eval-uated at rates of 2.2, 4.5 and 6.7 kg/ha. Thesetreatments resulted in a maximum control of 66,90 and 100%, respectively, of Chironomusmidges at 2-3 wk posttreatment.

The laboratory and field evaluations of B.t i.have shown that this biocide is effective mostlyagainst Chironomine midges, although ratherhigh rates of treatment (at least 10x or higherthe rates established for mosquito larvicidal ac-tivity) are required to achieve satisfactory larvalcontrol of midges in some situations (Rodchar-oen et al. 1991). The use of such elevated ratesof B.t.i. in midge control programs may be pos-sible in habitats ranging up to 50 or 100 ha, butwould not be economical or practical in largelakes, such as Lake Monroe in Florida or in theIagoon of Venice, Italy. Thus, there is a need todiscover new more toxic strain(s) of this biocideto be economically effective against chironomidIarvae.

Studies on B. sphaerlcus against chironomids(Ali and Nayar 1986, Sinegre et al. 1990, Rod-charoen et al. 1991) have shown that this bac-terium remains ineffective against midge larvae

266 JounNlr, oF THE AunRrclrl Moseurro CoNrRor Assoclarrorl V o L . 7 , N o . 2

at mosquito control rates or even at very highrates of treatment (11.2 and 22.4 ke/ha). "IheLCss values of G. paripes and C. crassicaudatusin the Iaboratory were >50 ppm for primarypowders of strains 1593 and 2362 of B. sphaeri-cus (Ali and Nayar 1986). Thus, strains 1b9Band 2362 of B. sphoericus known to be highlytoxic to some mosquito larvae (Ali and Nayar1986), do not offer any potential for midgecontrol.

Macroinuertebrate predators.. Many macroin-vertebrates in various phyla are predaceous onmidge larvae and pupae in nature. For example,there are several reports of leeches (Bay 1964,Bennike 1943, Elliott 1973, Mann 1952), dra-gonfly nymphs (Prichard 1964), and dytiscidbeetles and. Coelotanypus midges (Bay 196a)being predaceous on chironomids. Schuytema(1977), in his review of biological control ofaquatic nuisances, included predators of chiron-omids. Bay (1974) reviewed the subject of midgepredation by invertebrates and discussed thepredator-prey relationships of aquatic insects.So far, however, most accounts in the literatureconcerning midge predators are qualitative lab-oratory or field observations where predation bycertain invertebrates on midges was noted. Veryfew of these predators were subjected to quan-titative experimentation against midges.

The flatworm, Dugesia dorotocephala, is themost studied invertebrate predator of chiron-omid larvae. Under laboratory and semifield ex-perimental conditions, this planarian was shownto be quite effective in reducing midges (Legneret al. 1975b). Ali and Mulla (1983) evaluated D.dorotocephala against chironomids in experi-mental ponds during 3 consecutive summers. Ofthe different rates (10,25,50 and 100 planaria/m2) used, the rate of 50 planaria/m2 reducedmidge populations by 32-61% during the 3rd tothe 8th wk post-introduction ofthe predator. Inthese evaluations, the highest rate (100 plan-aria/m2) did not produce the maximum reduc-tion of midge larvae. This was perhaps becausethe abundance of the flatworm after a certainlevel was checked and regulated by higher pred-ators in the food chain in these ponds. Sincemass rearing of D. dorotocephala seems feasible(Tsai and Legner 1977), this predator warrantsfurther development for the biological control ofmidges. Also, D. tigrina should be evaluated asa predator of midge larvae since its productionand maintenance of large numbers are possible(Callahan and Morris 1989).

Predatory fish: There are numerous reports ofpredation by fish on chironomid midges (Bayand Anderson 1965, 1966; Ceretti et al. 198?,Cook 1962, 1964; Cook et al. 1964. Guziur 1976.Kajak et al. 1972, Kimball 1968, Kugler and

Chen 1968, Legner et al. 1975a, Mezger 1962,Zur 1980). These studies have shown that chi-ronomid larvae and pupae form a significantpart ofthe diet offish, including several sunfish,catfish, desert pupfish, young bass, carp, mos-quito fish, Tilapia and even gilthead seabream.Only the carp appears to have been successfulin causing appreciable reductions of midges infield trials (Bay and Anderson 1965, Mezger1967). Bottom-feeding fish, such as catfish, mayalso consume considerable numbers of midgelarvae, but do not produce significant reductionsof midge nuisance in situations of large midgepopulations where food supply of fish tends tobe continuously replaced as it is consumed(Hayne and Ball 1956).

The chironomid component in the diet of fishinhabiting a man-made reservoir in central Flor-ida was recently studied (A. Ali, unpublished).Foregut contents of 14 species of fish taken fromthe reservoir were examined. Of these, 3 speciesof sunfish, Lepornis macrochiru,s (bluegill), /,.megalntis (longear), and L. microlophus (redear),and one species of catfish, Ictaluris sp., hadconsumed appreciable numbers of chironomidIarvae and pupae. In the foregut of these 4species, midge larvae and pupae comprised 42*67% by volume, and 42-78% by wet weight, ofthe total food contents. The total number ofmidge larvae and pupae in the foregut of these10-25 cm long fish ranged from 4 to 45. Thus,predatory pressure by the use of these fish couldbe increased for the possible reduction of midgesin some habitats in Florida and elsewhere.

Quantitative evaluations of fish in waterspreading basins in the USA have shown thatcarp, Cyprinus carpio, and goldfish, Carassiusaurdtus, were effective in reducing midge popu-lations for a short time when stocked at 165-550 kg of fish/ha (Bay and Anderson 196b). Overthe long term, however, factors such as pondsiltation, filamentous algae and natural enemiestended to maintain larval populations at thesame level as did the 2 fish species. When thefish were removed from the basins, midge larvalpopulations increased only temporarily untilother controls interceded. The authors con-cluded that carp are less valuable for midgecontrol in large lakes and temporarily disruptedhabitats than in smaller sources of chironomidnuisance. Carp have also been used for the bio-logical control of midge larvae in Japan (Anon-ymous 1974), but no quantitative data on theireffectiveness are available. It should be under-stood that carp are prolific and aggressive fish.When introduced for midge control, they couldoutcompete the desirable species of fish andbecome a pest, inducing permanent and drasticalterations, similar to those produced by the

JUNE 1991 MlNlcnunnt oF PESTIFEROUS CHIRONOMTDAE 267

mosquito ftsh (Garnbusia affinis) in pond eco-systems (Hurlbert et al. L972).Introduction ofG. affinis had resulted in marked reduction ofzooplankton populations that fed upon phyto-plankton, thereby changing the water quality,as heavy algal blooms resulted due to the ab-sence of zooplankton. The possibility of indis-criminate or preferential feeding of the intro-duced fish on macroinvertebrate predators(midge predators), which are more efficient thanthe fish in having access to protective nicheswhere midge Iarvae prevail, may also disrupt thetrophic structure in the aquatic habitat. How-ever, in the presence of predatory fish, such asbass, the number of carp or other midge-preda-tory fish may be regulated, thus diminishing theundesirable effects produced by the latter.

The possible use of mosquito fish for midgecontrol was studied by Bay and Anderson(1966). They reported that although these fishfed upon chironomid Iarvae and emergingadults, no reduction in midge populations oc-curred even when the predator biomass reachedmore than 276 kg/ha. Cook et al. (1964) studiedthe impact of the fishery upon the midge popu-lation of Clear Lake, CA, and found that chiron-omid larvae and adults comprised the bulk ofthe summer diet of mosquito fish, but suggestedthat these fish feed on chironomid larvae whenunder food stress, concluding that mosquito fishare of little or no value in chironomid midgecontrol.

Legner and Medved (1973) and Murray (1976)studied the use of exotic fish, such as Tilapiaspp. for midge control and found them to behighly predaceous on midge larvae. However,Tilapia cannot withstand temperatures below10-12"C and would die each winter, requiringremoval of large numbers of dead fish from themidge breeding habitat, and their restockingduring summer. Additionally, there is a greatenvironmental risk involved with the introduc-tion of exotic fishes. They interact and competewith native fish and depauperate fish fauna, aproblem of great concern to fish and wildlifebiologists and conservation agencies. In severalinstances, introduction of mosquito fish intoNevada (western United States) had adverseeffects on the native fish populations (Deaconet al. 1964). Mosquito fish generally competeeffectively and may displace native species offish by consuming food and occupying theirniches (Deacon and Bunnel 1970). These con-siderations, thus, warrant great caution in ex-ercising the introduction and stocking of exoticfishes that offer potential for control of pestinsects.

In general, the biological control of midgesthrough the use of midge predatory fish would

be partially effective in small (<1-20 ha) andclosed habitats. However, for satisfactory midgecontrol in some situations, other possibilities ofcontrol in the integrated approach would berequired. Control of midges through the use offish in large and open habitats, such as LakeMonroe, FL, and the lagoon of Venice, Italy,would be relatively less effective because of thepossibility of fish displacement, due to their freemovement and migration.

Chemical: The chemical control of midges byIarviciding or adulticiding has primarily beenattempted in the USA and Japan (AIi 1980b,Tabaru et al. 1987). A few scattered and limitedmidge control studies (laboratory or field) havebeen made in other countries, such as the UnitedKingdom (Edwards et al. 1964), Egypt (Abul-Nasr et al. 1970, Brown et al. 1961), France(Sinegre et al. 1990), Italy (AIi and Majori 1984,Ali et al. 1985b) and others. A bibliography ofchemical control of chironomids was providedby Grodhaus (1975).

In the past 3-4 decades, the majority of chem-ical control work on midges in the USA has beenconducted in Florida (Patterson 1964, 1965; Pat-terson and von Windeguth 1964a, 1964b; Pat-terson and Wilson 1966, Patterson et al. 1966.AIi 1981b, Ali and Chaudhuri 1988, Ali and Lord1980, Ali and Nayar 1985, 1987; Ali and Stanley1981, AIi et al. 1987), Wisconsin (Hilsenhoff1959, 1960, 1962) and California (AIi and Mulla1976b, L977a, L977b,1978b; Ali et al. 1978, An-derson et al. 1964, 1965; Johnson and Mulla1980, 1981, 1982a; McFarland et al. 1962, Mullaand Darwazeh 1975, Mulla and Khasawinah1969, Mulla et al. 1971, 1973, t974,1975,1976;Norland and Mulla 1975. Norland et al. 1974.Pelsue and McFarland 1971. Pelsue et al. 1974).Occasional reports on chironomid control fromother states, such as New York (Jamnback 1954.1956), Maryland (Bickley and Ludlam 1968),Illinois (Polls et al. 1975) and others also existin the literature.

Numerous laboratory and field studies onmidge control were conducted in the past 2-3decades in Japan (Inoue and Mihara 1975, Ka-mei et al. 1982, Kudamatsu 1"969, Ohno andShimizu 1982, Sato and Yasuno 1979, Tabaru1975, 1985a, 1985b, 1985c, 1985d; Tabaru et al.1978, Tsumuraya et al. 1982a, 1982b; Yasuno etal. 1982. 1985).

Insecticides against chironomids were firstevaluated against midge larvae half a centuryago when Fellton (1940) used pyrethrins androtenone. These costly botanicals were used onlyfor a very short time because ofthe introductionof organochlorines, orthodichlorobenzene andtrichlorobenzene compounds, which yielded sat-isfactory control of Chironorntts and, Procla.dius

JounNa.r, oF THE AnpnrceN Moseurro CoNrRor, AssocrerroN V o L . 7 , N o . 2

midges (Fellton 1941). Subsequently, severalother organochlorines, such as DDT, DDD anddieldrin, afforded excellent control of midge lar-vae (Anderson and Ingram 1960, Anderson etal. 1964, Edwards et al. 1964, Flentje 1945b).However, the problem of toxicity of organochlo-rines to fish and other invertebrates in the foodchain (Hunt and Bischoff 1960), and the devel-opment of resistance in midge larvae (Lieux andMulrennan 1956), diverted the focus of midgecontrol to the use of organophosphate (OP) in-secticides. Several of these compounds wereevaluated by Hilsenhoff (1959), who reporteddichlorvos, trichlorfon, EPN, fenthion, mala-thion and phosdrin to be highly toxic to C.plurnosus larvae. Granular malathion was con-sidered a suitable insecticide to control this spe-cies (Hilsenhoff 1960, 1962).

In the early 1950s and 1960s in Florida, morethan 100 chemical compounds were evaluated inthe laboratory and/or field as potential larvi-cides of G. paripes. Benzene hexachloride andthe organophosphorus insecticide EPN were themost extensively used for midge control, buttheir use was generally discontinued by 1955,due to the development of resistance by midgelarvae (Patterson 1964, 1965). Control measureshad to be substituted by the use of fenthion andtemephos, and by adulticiding with thermal aer-osol fogs (Patterson and von Windeguth 1964b,Patterson et al. 1966). Fenthion as 1% granular(G) applied at 0.22-0.28 kg Allha controlled G.paripes for 3-10 wk, depending upon the time ofthe year; the duration of control was minimumin summer (Patterson and Wilson 1966). Te-mephos {l% G) applied at 0.06 kg Allha yieldedexcellent confiol of. G. paripes. In the last decade,several laboratory and semifield (experimentalponds) studies on the evaluation oforganophos-phates, pyrethroids and insect growth regulators(IGRs) (including chitin synthesis inhibitorsand juvenile hormone analogs) have been con-ducted (Ali 1981b, Ali and Chaudhuri 1988, AIiand Lord 1980, Ali and Nayar 1987, Ali andStanley 1981, Ali et al. 1987). The activity of anavermectin insecticide, abamectin, has also beentested in the laboratory against C. crassicauda-tus and G. paripes (Ali and Nayar 1985). How-ever, these studies remain of academic interestbecause no large-scale field trials using OPs,pyrethroids or IGRs in actual midge problemhabitats have been conducted in Florida in thepast 2 decades.

Laboratory eualuations: Organophosph.oruslnruici.d.es. Mulla and Khasawinah (1969) devel-oped a useful laboratory method for larvicidescreening and establishing susceptibility levelsof field-collected or laboratory-colonized midgepopulations to the candidate compounds prior

to their large-scale use in the field. This methodwas used to evaluate the OP insecticides chlor-pyrifos, temephos, fenthion, malathion, phen-thoate, ethyl parathion and methyl parathionagainst field-collected larvae from various hab-itats in southern California (AIi and Mulla1976b, 1977b, 1978b, 1980; Pelsue and Mc-Farland 1971). These studies showed that dif-ferent midge species manifested different de-grees of susceptibility to the compounds tested.For example, Iarval populations of C. decorusand Tanytarsu.s spp. drawn from the Santa AnaRiver spreading grounds were highly susceptibleto chlorpyrifos and temephos (LCgo = 1.5 and4.6 ppb, and 2.0 and 4.6 ppb, respectively), butCricotopus spp. in the same habitat were tolerantto all the OPs tested (LCeo : 0.L2-2.1ppm) (AIiand Mulla 1976b). Chlorpyrifos, temephos andphenthoate were also very effective against Chi-ronon'uts utahensistaken from Silver Lakes withLCso values of 7.8, 4.7 and 8.1 ppb, respectively.This species, however, was tolerant to methylparathion and fenthion (LCr' : 0.47 and 1.16ppm, respectively) (Ali and Mulla 1977b). Chi-ronomus decorus was most susceptible to chlor-pyrifos among all the OPs tested, but showed 5-74x tolerance to chlorpyrifos, temephos andmalathion when compared with the susceptibil-ity of C. utahensis to these compounds. Larvaeof Procladius spp. in Silver Lakes were the leastsusceptible to temephos and the most to chlor-pyrifos and phenthoate, while Cricotopus spp.were most susceptible to phenthoate and leastto methyl parathion (Ali and Mulla 1977b).Against Iarval populations from another resi-dential-recreational lake in southern California(Ali et al. 1978), chlorpyrifos was highly toxic toTanytarsus spp. (LCgo:3.1 ppb) andC. decorus(LCs6 = 1.4 ppb). Temephos and fenthion werealso considerably active against Tanytarsus spp.(LCeg : 7.2 and,8.8 ppb, respectively), butagainst P. freemarui, temephos was totally inef-fective, as indicated by the LCgo value of >5ppm. In the same study, fenthion showed pooractivity against C. decorus as well as against P.freernani, and malathion was also only slightlytoxic to P. freem,ani. In contrast to the midgesusceptibility results from the Santa Ana Riverspreading grounds and the residential-recrea-tional lakes, chironomid fauna (mostly C. deco-rus, D. californicus and, Cricotoprrs spp.) inhab-iting flood control channels, such as the CoyoteCreek system draining Orange and Los Angelescounties, CA (Ali et al. 1976a), were resistant tomost OPs, including chlorpyrifos, temephos,fenthion and malathion (LCgo : 0.16-42.14ppm) (AIi and Mulla 1980). Similar findingswere reported by Pelsue and McFarland (1971)

JUNE 1991 MeNncott,tnnr oF PESTTFER0US CHTRONoMIDAE 269

studying the midge problem earlier in the samechannel system.

More recently in Florida, chlorpyrifos, teme-phos, fenthion and malathion were evaluatedagainst field-collected larvae of G. paripes andC. crassicaudatus from Lake Monroe, andagainst C. decorus collected from 2 sewage oxi-dation ponds in Sanford, FL (AIi 1981b). Inthese evaluations, G. paripes exhibited the mostsusceptibility to malathion (LCso : 0.0079 ppm)and the least to temephos (LCr' : 0.022 ppm);C. crassicaudofus was generally tolerant to theseOP insecticides with LCee values ranging from0.14 ppm (chlorpyrifos) to 0.48 ppm (fenthion).Chironomus decorus was also relatively resistantto these compounds (LCe. : 0.1-0.38 ppm).

In Italy, the laboratory activity of chlorpyri-fos, temephos, malathion and fenthion was de-termined for field-collected C. salinarius larvaefrom the saltwater lakes of Orbetello (Ali andMajori 1984) and from the lagoon of Venice (Aliet al. 1985b). Among the OPs used, temephoswas the most active [(LCno : 0.021 ppm (lakes)and 0.027 ppm (lagoon)1, but the range of activ-ity of all the OPs tested was narrow (LCro :0.021-0.091 ppm), indicating that C. salinariuspopulations in the Iakes and in the lagoon weresusceptible to these compounds.

From Japan, Kudamatsu (1969) had reportedon the Iarvicidal activity of some OP insecticidesagainst field-collected C. plumosus. Sato andYasuno (1979) evaluated several insecticidesagainst larvae of C. yoshirnatsui, Polypedilumnubifer, Paratanytarsus partherngeneticus,Psectrocladius sp. and Procladius sp. Thesemidges, except fot Proclndius sp., were suscep-tible to temephos with LCso values ranging from0.0003 to 0.015 ppm. Tabaru (1985a) studied theIaboratory activity of chlorphoxim, chlorpyrifos,chlorpyrifos methyl and temephos against C.yoshimatsui. The same author also developedand described a unique criterion for determiningmidge larval mortality by observing the tube-building inability of intoxicated larvae providedwith 0.1-mm glass beads.

Pyrethroids: Several pyrethroids have beenevaluated in the laboratory against midge larvaedrawn from different habitats in California (AIiand Mulla 1978b, 1980; Ali et al. 1978), Florida(Ali 1981b) and Venice, Italy (Ali et al. 1985b).Evaluations made in California have shown thatdecamethrin (FMC-45498) and its chloro ana-logue FMC-45497 were highly active against C.utahensis, P. freemani and P. sublettei lawaedrawn from Silver Lakes, with LCgo values rang-ing from 0.13 to 0.77 ppb. Other pyrethroids,FMC-35171 and Pydrinu (SD-43775), were rel-atively less active against these species (Ali andMulla 1978b). Against Tanytarsus midges in-

habiting Village Grove Lake, CA, all 4 pyreth-roids were extremely toxic (LCso : 0.025-0.058ppb) (Ali et al. 1978). Decamethrin and its an-alogue were also highly active against C. decorusand P. freemani (LCeo : 0.76 and 0.5 ppb, and0.11 and 0.36 ppb, respectively). The pyrethroidFMC 35171 was also very effective against C.decorus and P. freemani inhabiting VillageGrove Lake, but Pydrin was moderately activeagainst C. decorus (LCs6 : 17 ppb) and, P. free-mani (LCso = 47 ppb). Midge fauna (mostly C.deconn, D. californicus, Cricotopus spp. and ?.grodhausi) of flood control channels, such as theCoyote Creek system and San Jose Creek, CA,were also highly susceptible to decamethrin andits analogue, FMC-45497 (LCro : 0.13-12.0ppb), but these midges showed lesser sensitivityto Pydrin (LCs1 : 33.0-420.0 ppb) (Ali andMulla 1980).

In Florida, several new experimental pyreth-roids (e.s., FMC-30980, FMC-33297, FMC-35171. FMC-45497. FMC-45499 and FMC-52703) were evaluated in the laboratory againstfield-collected G. paripes, C. crassicauddttl.s andC. decorus larvae (AIi 1981b). These pyrethroidsshowed a very high level of activity against the3 midge species, with LCgo values ranging from0.26 to 13 ppb. Of the 3 species, G. paripes wasthe most susceptible (LCeo : 1.3-9.8 ppb), fol-Iowed by C. decorus (LCno : 2.1-13.0 ppb).Among the pyrethroids tested, FMC-45499 andFMC-52703 were the 2 most toxic to the midgelarvae.

Evaluations of the pyrethroids cypermethrin,permethrin and deltamethrin against C. salinar-ius larvae collected from the lagoon of Venice,Italy, indicated the superior activity of cyper-methrin (LCeo - 0.34 ppb) and permethrin (LCgo: 0.3 ppb) against this saltwater midge. Delta-methrin was 13-14x less toxic to C. salinarius(LCso : 4.3 ppb) when compared with cyper-methrin and permethrin (Ali et al. 1985b).

Although most pyrethroids have proven to befar superior to OP compounds in activity againstchironomid larvae, the pyrethroids at mosquitoand midge larvicidal rates have a relatively lowindex of safety to nontarget invertebrates andfrsh (Mulla et al. 1978a, 1978b). Therefore, thefield use of pyrethroids as midge larvicides wouldbe limited to midge problem habitats such assewage ponds and wastewater channels wherenontarget invertebrates and fish would be ofminimal or no concern.

Insect growth regulators: With the advent ofinsect juvenile hormone analogue and chitinsynthesis inhibitory insect growth regulators(IGRs) such as methoprene and diflubenzuron,respectively, additional materials for midge con-trol have become available. Mulla et al. (1974)

270 JounNer, oF THE ArupRrclN Moseurro CoNrnol AssocrerroN V o L . 7 , N o . 2

evaluated several juvenile hormone analogueIGRs, Altosido (ZR-515 or methoprene), R-20458, RO-20-3600 and RO-8-5497 against OP-resistant and OP-susceptible population s of Chi-ronorn.r,s sp. larvae and found ZR-515 to be themost effective. The same IGR at 0.05 ppm in-duced complete inhibition of adult emergence inChironomus stigmaterus and ?. grodhausi col-lected from sewage oxidation ponds and exposedin the laboratory. Ali and Lord (1980) describeda laboratory bioassay technique for these IGRs(having delayed effects) against midges, andevaluated the chitin synthesis inhibitors diflu-benzuron, Bay SIR-8514 and Stauffer MV-6?8,and the JHA Stauffer R-20458 against 2 nui-sance midge species of Florida. In this study,diflubenzuron and SIR-8514 caused 90Vo mor-tality of C. decorus and G. paripes at 4-22 ppb,the LCeo of MV-678 for the 2 species rangedfrom 50 to 69 ppb, and R-20458 was the leastactive with LCe6 values of 0.24-03 ppm. In otherlaboratory studies in Florida, several new ben-zoylphenylurea IGRs (similar to diflubenzuron)were tested for activity against G. paripes and,C. decorus (Ali and Stanley 1981), and G. ponpesand C. tassicaudntus (AIi and Nayar 1987, Aliet al. 1987). The studies of Ali and Stanlev(1981) revealed that the IGR UC-62644 wasslightly more active than diflubenzuron againstG. paripes and C. decorus (LCgo values of 3.1ppb, G. paripes, and 5.7 ppb, C. decoruts). "Iherespective LCee values with diflubenzuron forthese species were 4.1 and 6.0 ppb. More re-cently, another IGR, UC-84572, was shown tobe even more toxic in the laborat ory to G. paripes(LCso : 0.58 ppb) and C. crossicau.datus (LCao :1.99 ppb) than diflubenzuron or UC-62644 (Aliand Nayar 1987). Four other benzoylphenylureaIGRs, UC-751 18, UC-7515 0, IJ C-7 87 2L and UC-76724, showed an LCgo range of 4.b-2b.8 ppbagainst C. crassicaudaf,us and 3.1-34.2 ppbagainst G. paripes. Among these, IJ C -7 67 2 4, w asthe most active against G. paripes (LCeo = 3.1ppb) as well as C. crassicau.datus (LCro : 4.5ppb) (Ali et al. 1987).

In addition to the IGRs, Ali and Nayar (19gb)have evaluated the laboratory activity of anavermectin microbial pesticide, abamectin,against field-collected. C. crassicau.datus and G.paripes larvae. Since avermectins exhibit de-layed toxicological effects (Wright 1984), theactivity of abamectin was compared with that ofdiflubenzuron, tested simultaneouslv as a stand-ard. A comparison of the LCso values revealedthat abamectin was slightly superior in activityto diflubenzuron against C. crassicau.d.atus (LCso= 1.63 ppb, abamectin, and 1.94 ppb, difluben-zuron) as well as G. paripes (LCsg : 1.b2 ppb,

abamectin, and 1.82 ppb, diflubenzuron) (AIiand Nayar 1985).

In Japan, the IGRs methoprene and difluben-zuron were tested againstC. yoshimatsui (Kameiet al. 1982, Tabaru 1985d). Both IGRs provedhighly effective at concentrations of <0.001ppm, but diflubenzuron showed superior activityover methoprene (Tabaru 1985d). Currently,these IGRs are being evaluated in the laboratoryin Italy, against field-collected C. salinarius fromthe Venice lagoon (S. Della Sala, personal com-munication).

It is obvious from the laboratory studies thatthe levels of susceptibility of various midge spe-cies or genera to different insecticides vary con-siderably. Even the same species in differentgeographical locations may show different levelsof susceptibility to a chemical. The existing var-iation of species composition between habitatsfurther complicates the problem. Thus, eachhabitat requires an independent approach forthe chemical control of midges.

FieLd studies: Adult controL In the 1950s and1960s, adulticiding was the principal means ofmidge control in Florida. Malathion and mala-thion-Lethane or naled were used as thermalaerosol fogs. Application of these materials wasmade from trucks, boats and airplanes. Lowvolume aerial sprays of malathion at 0.14-0.27kg AI/ha were very effective. At the higher rate,malathion controlled G. paripes within 3 h andthe control lasted for 4 days (Patterson et al.1966). Although midge adulticiding proved ef-fective, fogging has its limitations for controllingthese insects. Presently, no specific insecticideis registered by the United States Environmen-tal Protection Agency for adulticiding midges.However, some OP compounds, pyrethroids andother insecticides labeled for adult mosquitocontrol in the USA (Rathburn 1988) probabtyreduce some adult midge populations when usedby mosquito control agencies for the control ofadult mosquitoes in some situations. Rathburn(1988) provided comprehensive information onlabel recommendations of 16-20 insecticides foruse as ultralow volume (ULV), low volumesprays, ground applications, thermal aerosols inground applications and mists in ground appli-cations in adult mosquito control programs. Thelabel requirements for droplet size of ULV andnonthermal aerosols for adult mosquito controlwere also provided. Because of the rapidly es-calating problem of midge nuisance in the USA,federal and/or state registration of some insec-ticides as midge adulticides is needed.

Insecticides as midge adulticides are used ona very limited basis in Japan (Y. Tabaru, per-sonal communication). However, in Italy, aerialapplications of deltamethrin and malathion are

JUNE 1991 MeNecrnanlr oF Ppsurrnous CHIRONoMIDAE .,n1

the only means of control of adult C. salinariusin and around Venice (F. D'Andrea, personalcommunication).

Larual control: Organophosphorus laruicides.A number of OP insecticides in different for-mulations were evaluated in several residential-recreational lakes and in the Santa Ana Riverspreading system in California by Ali and Mulla(1976b, t977a,1977b, 1978b), and Mulla et al.(1971, 1973, 1975). Chlorpyrifos at rates rangingfrom 0.11 to 0.28 kg AI/ha gave excellent controlof tanypodine and chironomine midges in LakeCalabasas and Westlake (Mulla et al. 1971,1973), Spring Valley Lake (Mulla et al. 1975)and Silver Lakes (Ali and Mulla 1977b). Theduration of control varied from 1 to 5 months,depending upon the rate oftreatment and natureof the habitat. In 4-5 m deep Spring ValleyLake, when applied at 0.28 kg AI/ha, controllasted for over 1 month (Mulla et al. 1975); whilein 1-2 m deep Lake Calabasas, chlorpyrifos at0.22k5 l\I/haprovided midge control for at least4 months (Mulla et al. 1971). The granularformulation gave better (magrritude) and longer-Iasting control than the emulsifiable concen-trate formulation (Mulla et al. 1971, 1975).Chlorpyrifos was also reported to provide satis-factory control of C. raparius in sewage channelsin Chicago, IL (Polls et al. 1975).

Field evaluations of temephos indicated thatthis OP insecticide was effective against somemidge species in residential-recreational Iakesand other midge habitats in California, butyielded control for shorter durations than chlor-pyrifos, even though the rates of applicationwere much higher than those employed forchlorpyrifos. In water percolation basins, teme-phos at 0.27-0.38 kg AI/ha gave a maximum of78Vo conftoI of midges (mixture of Tanytarsus,Chironomus and Procladiu.s) for 1 wk posttreat-ment (Johnson and Mulla 1980). At higher rates(0.56-0.84 kg Allha) temephos controlledmidges for 4-5 wk in Lake Calabasas and SpringValley Lake (Mulla et al. 1971, 1975), while atlower rates (0.17-0.28 ke AI/ha) in the SantaAna River basin and in Silver Lakes, it producedsimilar results (Ali and Mulla 1976b, 1977b).Later treatments of Silver Lakes with temephosat 0.28 kg AI/ha produced complete control ofTanytarsus spp. for 2 wk, but Procladius spp.and C. decorus remained unaffected. Evenhigher rates of temephos (0.33 and 0.56 kg AI/ha) failed to produce satisfactory control of Cdecorus andProcladius spp. in the lake (Johnsonand Mulla 1981). In Westlake, CA, temephoswas also not effective at 0.56 kg AI/ha (Mullaet al. 1971). Generally, temephos was effectiveagainst Chironomini in most situations, butcaused only slight or no mortality in Tanypodini

(mostly Procladius spp.). Temephos, in granularformulations, is the sole insecticide registeredby the United States Environmental ProtectionAgency for use as a larvicide against nuisancemidges, and only in standing water situations.

Among other OPs, fenthion at 0.56 kg AI/haprovided satisfactory midge control for >7 wkin Lake Calabasas, and for 4 wk in Spring ValleyLake, but remained ineffective in Westlake at0.56 kg Allha (Mulla et al. 1971, 1975). Mala-thion and phenthoate applied at 0.56 kg Allha,yielded good control of midges for 2-3 wk inSpring Valley Lake; methyl parathion at thesame rate of application produced marginalmidge control (Mulla et al. 1975).

In Japan, in outdoor model streams, temephosand chlorphoxim applied at 2 and 5 ppm, re-spectively, caused drastic larval reductions ofThiene manniella rnaj uscula, P aratrichocladiusrufiuentris and Chironomus flauiplurnus, butthese species recovered within 2-3 wk posttreat-ment (Yasuno et al. 1985). In wastewater, te-mephos has been successfully used at 2 ppmmaintained for 20 min in the gutters to controlC. yoshimatsui (Inoue and Mihara 1975). Thesame rate of temephos and chlorpyrifos methylmaintained for 30 min in the gutters, disinfect-ant tanks and effluent discharge channels ofsewage treatment plants gave excellent controlof C. yoshimatsui (Tabaru 1985b). Tabaru (1975)and Tabaru et al. (1978) reported satisfactorycontrol of C. yoshim.atsui for 3 wk in pollutedrivers by using temephos at rates of 0.69-1 ppmmaintained for 60 min; the insecticide was car-ried up to 3,000 m downstream from the appli-cation site. Chironomus yoshimatsui in anotherriver was successfully controlled at rates of 0.9-2.0 ppm of temephos maintained for 60 min(Ohno and Shimizu 1982). In other studies, te-mephos applied at rates of 0.05-1 ppm providedexcellent control of Polypedilum nubifer, Crico-topus bicinctus, Chironomus kiiensis and Chiron-omus tainanr"rs inhabiting eel culturing ponds(Ohkura and Tabaru 1975, Yasuno et al. 1982).

Overall, the field studies on OP insecticidesagainst midges in the USA and Japan haveindicated that chlorpyrifos, chlorpyrifos methyl,temephos, chlorphoxim and a few other OP com-pounds were effective against most nuisancespecies of midges, suppressing the Iarval popu-lations for 2-b wk or longer at application ratesbelow 0.56 kg AI/ha (USA) and <1-5 ppm (Ja-pan). These studies were not intended to eradi-cate midge larvae, but were implemented to re-duce and maintain midge populations below thelevels at which they pose pest problems. Also,the repeated and prolonged use of insecticidesmay result in buildup of resistance in midgeIarvae, as occurred in Florida due to the pro-

272 JouRrnl oF THE AunRrclrl Moseurro CoNrRor, AssocrlrloN VoL. 7, No. 2

longed use of EPN and BHC (Lieux and Mul-rennan 1956), In some storm drains and floodcontrol channels in California. most OPs. in-cluding chlorpyrifos and temephos, have becomeineffective against midge larvae even at 1.1 kgAI/ha rate of treatment (Pelsue and McFarland1971). In the Chicago area, C. raparius has de-veloped resistance to chlorpyrifos due to therepeated use of this OP insecticide (I. Polls,personal communication). In Silver Lakes, CA,a considerable decline in the effectiveness ofchlorpyrifos and temephos was noted after re-peated use ofthese compounds against C. utah-ensis, C. decorus, P. freemani and P. sublettei(AIi and Mulla 1978b). Resistance levels in thesespecies to some other OPs not used in the fieldalso increased, indicating the phenomenon ofcross-resistance within the OP group.

The frequent and extensive use of temephos,and to an extent fenthion, has caused the devel-opment of resistance in C. yoshimotsui in theKanda River, Tokyo (Ohno and Okamoto 1980).Tabaru (1985c) has also indicated a widespreadacquired resistance to fenthion in C. yoshimatsuicollected from 10 different rivers in Japan. How-ever, larvae from all of these rivers were suscep-tible to chlorpyrifos methyl, and temephos wasstill considered to be economically effectiveagainst C. yoshirnatsui in about 50% ofthe hab-itats exposed to the OP insecticide.

Insect growth regulators: Pioneering fieldstudies on the use of IGRs for midge control arethose of Mulla and Darwazeh (1975) and Mullaet al. (L974,1976) who reported on the activityof methoprene and diflubenzuron againstmidges. These two IGRs, in different formula-tions, were evaluated in California in residen-tial-recreational lakes (Ali and Mulla 1977b, AIiet al. 1978, Mulla et aL 1974, 1975, 1976), andin the Santa Ana River basin (Ali and Mulla1977a). In these studies, methoprene at 0.28 kgAllha controlled midges for 1-2 wk by inhibitingadult emergence (Mulla et aI. L974,1976), whilediflubenzuron at 0.11-0.28 kg AI/ha inducedmidge control for 4-8 wk at the highest rate oftreatment (Mulla et al. 1976). In one study inresidential-recreational lakes in California, di-flubenzuron at 0.11 and 0.28 kg AI/ha com-pletely suppressed emergence of Tanytarsus andProcladius midges for 2 wk posttreatment, butwas not as effective against C. decorus (Johnsonand Mulla 1981). The same study indicated thatSIR-8514 applied at the same rates of difluben-zuron gave similar results. The authors sug-gested that higher rates of application of the twoIGRs may produce satisfactory control of C.decorus in the lakes. Johnson and Mulla (1982a)evaluated 2 formulations (25 WP and 0.5% G)of SIR-8514 in ponds on a golf course in Cali-

fornia. These ponds ranged from 0.25 to 2.5 hain surface area and <1 to 2.5 m in depth. TheWP, applied at 0.11 and 0.28 kg Allha, inhibitedadult emergence of Tanytarsus, Chironomlrs andProcladius midges for 2 wk, while the granularformulation at the same rates effectively sup-pressed adult eclosion of these chironomids forup to 4 wk after treatment. The duration ofcontrol resulting from the lower rate of treat-ment of each formulation was almost the sameas produced by the higher rate.

Under semifield conditions in shallow exper-imental ponds in Florida, a 257o WP and a l%granular formulation of SIR-8514 at 56 and 112g Al/ha gave excellent overall control of Tany-forsus spp., G. holoprasinrzs and C. decorusmidges for ca. 3 wk. Diflubenzuron25 WP at 28and 56 g AI/ha was slightly more effective thanSIR-8514 and far more than MV-678 applied atcomparable rates (Ali and Lord 1980). Theseauthors also showed that SIR-8514 at 70 g AIIha completely suppressed adult emergence ofmidges in a sewage pond for at least 10 daysafter treatment. In another study in the sameponds, a 25 WP formulation of the benzoylphen-ylurea IGR, UC-62644, was tested againstmidges at 25, 50 and 100 e Al/ha (Ali andStanley 1981). All 3 treatment rates producedexcellent control of midges for more than 4 wk.Even the lowest rate (25 e Al/ha) induced 94-99% inhibition of midge emergence during the 4wk of the evaluation period. The WP of UC-62644 was also applied at 100 g AI/ha in a golfcourse pond in Florida, and gave good control(53-98%) of the predominant midge species,Chironomus carus,in the ponds during the 4 wkofevaluation (AIi and Stanley 1981). Less than6 years ago another benzoylphenylurea IGR,UC-84572, became available for testing againstmidges. A 10 EC formulation of this IGR wasevaluated at 1, 5 and 10 ppb AI in the experi-mental ponds in Florida. Diflubenzuron (Dimi-lin 25 WP) at 10 ppb AI was simultaneouslytested as a standard in ponds because of its largedata base. Emergence of adult C. decorus, C.stigmaterus, G. holoprasinus and Tanytarsiniwas inhibited by UC-84572 as well as difluben-zuron (Ali and Chaudhuri 1988). Even at 1 ppb,UC-84572 caused a maximum of g0% inhibitionof emergence of. C. decorus, 66Vo each of C.stigmaterus and G. holoprasinus, and 53% ofTanytarsini, 2 days after treatment. However,the overall reduction of total adult midges at 1ppb ranged from 0 to 67% during the 28 days ofposttreatment evaluation. The rate of 5 ppb gavecomplete control of G. holoprasinus, a maximum99% reduction of C. decorus and94% reductioneach of C. stigmaterus and Tanytarsini, with anoverall 96Vo conftol of total chironomids. At 10

JUNE 1991 MANAGEMENT or PosrlrgRous CHIRoNoMIDAE

ppb, UC-84572 caused complete inhibition ofadult emergence within 2 days posttreatment,Iasting for 2 wk for C. stigmaterus, l wk for C.decorus and <1 wk for G. holoprasintzs and Tan-ytarsini. Diflubenzuron at 10 ppb also inducedcomplete inhibition of adult midge emergence,but it lasted for (1 wk for all midge speciesexcept for C. stigmatferus, which was controlledfor X wk. A comparison of the activity of UC-84572 with that of diflubenzuron applied at thesame rate, 10 ppb, revealed that UC-84572 gen-erally produced slightly longer lasting control ofC. decorus, C. stigmaterus and G. holoprasinusthan diflubenzuron. Emergence of Tanytarsini,however, remained suppressed for longer periodsof time in the ponds that were treated withdiflubenzuron.

In 1990, four formulations, liquid (AltosidLiquid Larvicide or A.L.L.), granular (SAN 810I 1.3 GR), Altosid pellet and Altosid XR (ex-tended residual) briquet of the juvenile hormoneanalogue IGR methoprene were evaluated forefficacy against midges including C. decorus, C.stigmaterus, G. holoprasinus, Polypedilun'L spp.and Tanytarsini in experimental ponds (eachpond 24 m2 containing 0.5 m deep water) inFlorida (A. Ali, unpublished). In this study,A.L.L. at 2 rates 0.293 and 5.86 liters/ha, Bratr-ules at 13.0 kg/ha, pellets at 5.6 kg/ha andbriquets at the rate of 3/pond were each appliedto 3 separate ponds. Three ponds were left un-treated as controls. The A.L.L., granular, pelletand briquet formulations contained 5.0, 1.3, 4.0and t.8% of (S)-methropene, respectively. Thisstudy indicated that A.L.L. at 0.293 liters/haremained ineffective, but at 5.86 liters/ha, itreduced emergence of midges by 74-99% for 2wk posttreatment. Midge emergence returned topretreatment or higher levels in the 3rd wk aftertreatment. The granular formulation reducedemergence of midges ftom 6l-87% in the 2 wkafter treatment. The effectiveness of the gran-ular formulation was totally lost in the 4th wkposttreatment. The pellet and the briquet for-mulations produced greater control of midgesfor a longer duration as comparedwith the liquidand the granular formulations. The pellet for-mulation gave a maximum of 98% control at 3days after treatment, with the level of contro.gradually declining and fluctuating between 64and 90% for the 1-7 wk posttreatment. Thebriquet formulation gave 66-96% control ofmidges during 35 days posttreatment, withemergence of adult midges reducingby 98% after7 days posttreatment. Generally, the pellet for-mulation provided control equal or better thanthe XR briquets with almost 1/4th the activeingredient.

The IGRs, diflubenzuron and methoprene,have been used in Japan for controlling C. yosh-imatsuL Treatments of 2 rivers with the formerIGR at 1 ppm maintained for 60 min resulted inexcellent control of C. yoshirnotsui for 3 wk.Methoprene at the same dosage proved less ef-fective than diflubenzuron in the same river(Tabaru 1985d). In the gutters and dischargechannels of sewage treatment plants, metho-prene was applied at the rates of 0.13 and 4 ppm,but was effective against C. yoshimatsui only atthe higher rate (Tsumuraya et al. 1982b).

The laboratory and field studies on IGRsagainst midges have shown that many of thesecompounds are highly effective against mostchironomid species. These compounds are dif-ferent from insecticides. such as OP larvicides,in that they inhibit larval or pupal developmentto the adult stage without reducing larval pop-ulations to the extent and magnitude of someOP insecticides, such as chlorpyrifos and teme-phos (Ali and Mulla I977a, t977b). Therefore,these compounds may have Iess of a decimatingeffect on an important component of the foodchain. The IGRs also offer a good potential asadditional tools for control of midge speciesresistant to OP insecticides. It has been docu-mented that several of these IGRs, as well asOP larvicides, may have temporary or chroniceffects on nontarget aquatic biota coexistingwith midge larvae (Ali and Mulla 1978c, 1978d).Mulla et al. (1979) provided an excellent reviewof some 200 published papers covering the ef-fects ofpredators, biocides, insecticides, and in-sect juvenile hormone analogue and chitin syn-thesis inhibitor growth regulators on nontargetbiota associated with a variety of mosquito hab-itats. However, the severe nuisance and eco-nomic problems posed by adult midges and theirrecently discovered association with problems ofallergy in humans, warrant availability of newtools, such as diflubenzuron and methoprene(particularly the pellet formulation), for midgecontrol in selected habitats. These IGRs shouldbe useful especially in polluted habitats whereimpact on nontarget organisms and the ecolog-ical balance of the habitat would be of minimalconcern. In some situations, only partial areasof a habitat that support heavy populations oflarval midges need to be treated (Ali and MullaL977b). This practice would not only reducesome midge nuisance, but would also help inquicker restoration of the lost nontarget inver-tebrates from the untreated areas. The toxiceffects of the chemical used in these habitatswould also diminish sooner due to dilution.

Presently, diflubenzuron has a state registra-tion (24c) for use against midges by the Califor-nia Department of Food and Agriculture. Such

JouRNu oF THE Altnnrclu Moseurro Cournol Assocr.qtrorl V o L . 7 , N o . 2

a registration of diflubenzuron should also beconsidered in other states. Also, methoprenewarrants a similar registration.

SUMMARY

In many parts of the world, water bodies inurban and suburban areas exposed to intensivehuman use have become increasingly eutrophicand favorable for the profuse breeding of chiion-omid midges. Some of these habitats supportlarval densities in excess of 40,000/m,, resultingin massive emergences of adult midges that posea variety of nuisance, economic and occasionallvmedical problems for the nearby residents. Inthe past 2-3 decades, numerous habitats sup-porting primarily Chironomini species in theUSA, Italy and Japan have been the focus ofcontrol studies.

A variety of chironomid control methods havebeen investigated in the past 2-3 decades, witha majority dealing with chemical control. Anumber of parasites and pathogens, such as vi-ruses, rickettsiae, protozoans, nematodes andfungi have been reported from midges in differ-ent parts of the world but verv few of thesemicrobial organisms have been subjected tomass culturing and inoculating of natural breed-ing sources for quantitative biological contro-assessments. Physical and cultural controlmethodologies of chironomids are also the leastexplored.

A large number of organochlorines, organo-phosphates (OPs), pyrethroids and insectgrowth regulators (IGRs) including juvenile hor-mone analogues (e.g., methoprene) and chitinsynthesis inhibitors (e.g., diflubenzuron) havebeen evaluated in the laboratory and/or in thefield against nuisance species of midges in theUSA and Japan. Among the OP compoundstested, chlorpyrifos and temephos were gener-ally toxic to field-collected larvae of Chironomusdecorus and C. utahensls (Californi a), Glyptoten-dipes paripes (Florida), C. yoshimatsui and C.plurnoas (Japan) and C. salinarius (Italy), butsome of these and a few other species of midgesin some situations in the USA and Japan weretolerant to temephos. There is also evidence ofcross-resistance in chironomid larvae to the OPgroup. Presently, temephos is the only registeredmidge larvicide in the USA. Field studies on OPinsecticides against midges in the USA and Ja-pan have indicated that chlorpyrifos, chlorpyri-fos methyl, temephos, chlorphoxim and a fewother OP compounds caused appreciable larvalreductions fot 2-5 wk or longer at rate below0.56 kg AI/ha (USA) and <1-5 ppm (Japan).Numerous pyrethroids have exhibited far supe-rior activity than OP insecticides against chiron-

omid larvae, but most pyrethroids at mosquitoand midge larvicidal rates would have a rela-tively low index of safety to nontarget aquaticinvertebrates and fish.

The IGRs, methoprene, diflubenzuron andseveral benzoylphenylurea compounds (similarto diflubenzuron), have shown superior activityagainst a variety of midge species in Japan andthe USA. Some species exhibited an LCgo value<1 ppb to experimental benzoylphenylureas,such as UC-84572. In the field, methoprene,diflubenzuron, Bay SIR-8514 and several otherbenzoylphenylureas were highly effective, yield-ing midge control for several weeks at rates (0.8kg AI/ha. A new pellet formulation of metho-prene at 0.22 kg AI/ha suppressed emergence ofadult midges by 64-98% in experimental pondsfor 7 wk posttreatment. Generally, diflubenzu-ron showed superior activity over methoprenein several field studies. The 2 IGRs are excellentcandidates for controlling midges, particularlythe OP-resistant species, and warrant registra-tion in the USA. Diflubenzuron and methopreneare presently being used in Japan for midgecontrol.

Among biological control agents, Baciltus thu-ringiensis serovar. israel,ensis (B.t.i.) reducedmidge larvae to various degrees in some pondsand lakes. However, the application rates ofB.t.l., needed for the satisfactory control (90%or higher) of midges, were at least 10x or higherthe rates established for mosquito control; there-fore, B.t.i. may have limited scope for use inmidge control programs. The flatworm, Dugesiadorotocephala and some fish (e.g., carp, sunfish,catfish, Tilapia and others) have been reporteito be effective in reducing midge larvae in somesituations. Fish, as predators of midge larvae,however, are considered to be partially effectiveand only in small (20 ha or smaller) and closedhabitats. These predators would be less effectivein midge habitats covering several hundred orthousands of ha, particularly those that are con-nected to river systems where they may be dis-placed due to their free movement and migra-tion. More research on the development andquantitative field assessments of promising par-asites, pathogens and predators of midge larvae,and the environmental implications and impacton trophic structure of these biological controlagents in the aquatic environment is needed.

Midge habitats that spread over severalhundred or thousands of ha demand explorationofphysical and cultural control methods. In suchhabitats, the physical and chemical compositionof substrate materials and chemistry of the over-lying water in relation to spatial and seasonaldistribution of midge larval populations mayprovide a clue to the conditions conducive to

JUNE 1991 MANAcEMENT op Pnsrrrenous CHIRoNoMIDAE 275

their proliferation, and the ecological basis ofmidge production. Their proliferation could thenbe discouraged by manipulating their environ-ment. Information related to adult dispersal be-havior, patterns of abundance, diel periodicityof eclosion and attraction to light could also bemanipulated in some situations to reduce midgenuisance more economically. Thusfar, very fewstudies on the larval ecology and adult behaviorof pestiferous Chironomidae have been under-taken.

ACKNOWLEDGMENTS

This is Florida Agricultural Experiment Sta-tions Journal Series No. R-00920. Gratitude isexpressed to Marshall Laird and an anonymousreviewer for their useful suggestions that im-proved the quality of this article. Constructivecriticism ofthis paper by John L. Capinera andDonald R. Barnard and Kenneth E. Savage isalso appreciated. I dedicate this article to mydaughter and son, Khudejah Iqbal Ali and UmerMeraj Ali.

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