Insect pollinators and sustainable agriculturePeter G Kevan E Ann Clark and Vernon G Thomas

Abstract Underestimation of the pivotal role played by managed and native insectpollinators is a key constraint to the sustainability of contemporary agricultural practicesThe economic value of such insects to pollination seed set and fruit formation greatlyoutweighs that suggested by more conventional indices such as the value of honey andwax produced by honeybees Although the European honeybee has been widely regardedas the single most important pollinating species the increasing spread of trachael andVarroa mites and Africanized bees threatens the distribution and magnitude of tradi-tional honeybeekeeping enterprises in North America A number of other bee and insectpollinators such as orchard bees bumblebees and squash bees which are not affectedby either the mites or the Africanized bees are considered as likely candidates formanagement and use in commercial agriculture An additional role can be played bynative or wild pollinators provided that attention is given to curtailing of populationlosses caused by both inadvertent insecticide poisoning and habitat destruction To ensurea reliable source of pollinators both managed and native a more comprehensive strategyfor management of crop pollination is needed Elements of this strategy include anincreased understanding of the biology and ecology of pollinating insects as well asproviding appropriate nesting habitat and ensuring the availability of alternative sourcesdegf forage99 to sustain populations when the target crops are not in bloom Examplesare discussed to illustrate how private initiatives and changes to public policy can enhancepollinator habitat and ultimately agricultural productivity

Key words orchard bees bumblebees squash bees ecology habitat conservationprivate initiatives public policy alternative pollinators

Introduction

Agriculture that is sustainable explic-itly recognizes its ecological foundations(Commoner 1972 Altieri 1987) Con-versely agricultural practices which failto acknowledge and enhance flows ofenergy and material through naturalprocesses or worse which eclipse anddisrupt such processes become increas-ingly dependent on exogenous subsidiesof energy and material to sustain pro-ductivity (Clark and Christie 1988) Atpresent design and management of sus-tainable agricultural systems are at riskbecause of ignorance of the contribution

Peter G Kevan is Associate Professor of Environmen-tal Biology E Ann Clark is Assistant Professor of CropScience and Vernon C Thomas is Professor of ZoologyUniversity of Guelph Guelph Ontario NIG 2W1 Can-ada

of managed and native insect pollinatorspecies to the function of ecosystemsand specifically to managed agroeco-systems

Principles of pollination

Pollination is the first step in the sex-ual reproduction of plants It is thetransfer of pollen from the male organsor anthers to the female receiving ele-ments the stigmata As such pollinationis an essential prerequisite to seed andfruit development on most temperateand tropical crops Furthermore irre-spective of whether or not the crop com-modity is cereal oilseed vegetable orforage seed production for replantingmost agricultural and horticulturalcrops also relies on pollination Thus itmay truly be said that pollination is apivotal keystone process in both naturaland managed ecosystems (Kevan and

Baker 1983 1984)Self-pollination and cross pollination

(Figure 1) may be effected by gravitywind or animals (mostly insects) Somecrops such as varieties of soybean (Gly-cine max (Merrill) L) and barley (Hor-deum vulgare L) are self-pollinatingbefore the flowers open (cleistogamy)Others which are self-pollinating and en-tirely self-compatible are pollinated afterthe flowers open (chasmogamy) a com-mon situation for crop plants and weedsNevertheless even some self-pollinatingcrops produce better when outcrossingoccurs as has been found in canola(Brassica napus L) (Kevan and Eisi-kowitch 1990) and in self-compatiblevarieties of sunflower Helianthus an-nuus L) (Freund and Furgala 1982)and soybean (Erickson et al 1978) Inself-incompatible plants self-pollinationwill not effect fertilization and outcross-ing is required as for many stone andpome fruits

Floral morphology reflects the meansof pollination For example wind is theprimary agent of pollen transfer in for-age grasses which are equipped withlarge feathery stigmata prolific pollenproduction and inconspicuous flowersBut for many species with colorfulscented and conspicuous flowers pol-lination is the outcome of the lengthycoevolution of plants and their pollina-tors (Crepet 1983) The most abundantand diverse pollinators are insectswhich may transfer pollen within oramong flowers on the same plant as inself-pollinating species or between flow-ers on different plants as is required byobligately cross-pollinated species

Insect pollination in agriculture

The importance of insect pollinationhas been documented in treatises by Free(1970) McGregor (1976) and Pessonand Louveaux (1984) The economicvalue of insect pollination to all agri-cultural production in Canada and the

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Figure 1 Cross and Self Pollination

USA has been estimated at $12 and$19 billion respectively (Winston andScott 1984 Levin 1983) In addition tothe value of honey and wax producedby honeybees these figures reflect thefar greater contribution of insects to seedset and fruit formation in commerciallygrown crops More recently Robinsonet al (1989) have reviewed the contri-bution of honeybees alone to crop pro-duction and arrived at a figure of $93billion annually in the USA

Because of its manageability and de-gree of domestication the European ho-neybee Apis mellifera L has come to beregarded as the single most importantpollinating species (Free 1970 Mc-Gregor 1976 Jay 1986) As large fieldmonocropping and chemically intensiveagriculture have become more prevalentreliance on managed bees especially ho-neybees has grown Moreover removalof wild lands through agricultural ex-pansion has disrupted the habitat of na-tive pollinators Insecticide applicationhas killed them directly and herbicideuse has extirpated alternative pollensources from their natural forage species(Kevan 1975 1986)

At present impending risks associ-

ated with the overdependence of large-scale agriculture on honeybees for com-mercial scale crop pollination are be-coming increasingly apparent (Robinsonet al 1989) One threat comes from par-asitic trachael mites (Acarapis woodiRennie) and varroa mites (Varroa jacob-soni Oudemans) which have severely af-flicted the US honeybee industry(Morse 1988) and which will in all like-lihood be prevalent in Canada withinseveral years Effective control of theseexotic parasites which affect only ho-neybees is not simple and practical con-trol measures are still underdevelopment Another threat is that ofthe Africanized (or killer) honeybeewhich is rapidly expanding its range inNorth America (Needham et al 1987Morrison 1989) Little is known aboutthe effects this aggressive and difficultto manage honeybee will have on croppollination (Danka and Rinderer 1986)In addition honeybees do not pollinateall kinds of crops with equal efficiencyare not active under all climatic condi-tions and may show species preferences(Kevan 1987) Conversely other speciesof bees may pollinate some crops athigher levels of efficiency with lower

population densities and with greaterindependence of climatic conditions(Boyle-Makowski 1987 Torchio 1987)

Accordingly the position advocatedin this paper is for recognition of thelimitations of honeybees and for an ex-panded role for native species in thecommercial pollination of cultivatedcrops We examine how natural polli-nators as a component of agroecosys-tems can be enhanced as a reliableadjunct to honeybees Finally we inves-tigate the conditions which must be sat-isfied including habitat alternativeforage reduction of chemical pollutantsand shelter for such native species toplay a realized economic role in modernagroecosystems

Pollination and foodproduction

Crops and their pollination

The central role of pollination in ag-riculture is illustrated in Figure 2 Fa-miliar foods which depend entirely orpartially on insects for pollination in-

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INSECT POLLINATION amp THE CONSUMERIi

Processed

Fruits ampBerries

Hi Seeds - gt bull Vegetables ^ | | i j | | ^ | | | | | l ^ Oil Seeds - bull Processed

illiiiir Processec|8li Forage Livestock

vLivestock Seed Processed

Livestock

Figure 2 Insect Pollination and the Consumer

elude apples (Pyrus malus L) pears (Pcommunis L) blueberries Vacciniumspp) strawberries (Fagaria x ananassaDuchesne) raspberries (Rubus spp)cherries (P avium L) pumpkins (Cu-curbita pepo L) squash (C maximaLam) oranges (Citrus sinensis Osbeck)almonds (P amygdalus Stokes) and ahost of others in temperate and tropicalparts of the world (Free 1970 Mc-Gregor 1976) Oilseed crops such as oilpalm (Elaeis guineensis Jacq) and somevarieties of rapeseed (Brassica spp) andsunflower (Helianthus annuus) are alsodependent on insect pollination as areforage legumes such as alfalfa (Medicagosativa L) and the clovers (Trifoliumspp)

Some fruits (in the botanical sense) donot benefit from insect pollination Windpollination is well known in cereals andin walnuts (Juglans spp) hazelnuts(Coryllus spp) olives (Olea europea L)dates Phoenix dactylifera L) pistachio

(Pistacia spp) grapes (Vitis vinifera L)(Pesson and Louveaux 1984) conifersand many trees of the temperate zoneOthers such as tomatoes (Lycopersiconesculentum Mill) bell peppers (Capsi-cum annuum L) eggplant (Solanummelongena L) some beans (Phaseolusvulgaris L) oilseed crops such as soy-bean and flax (Linum usitatissimum L)are easily self-pollinated either sponta-neously or by some wind agitation Inaddition bananas (Musa sp) and saladlong cucumbers (Cucumis sativa L) pro-duce fruit without pollination

Although much is known about croppollination areas of considerable igno-rance remain Much of the acceptedknowledge on crop pollination is nowout of date some has little scientific ba-sis some is long-cited but unsubstan-tiated opinion and some is simplywrong There is no reliable compendiumof information on pollination require-ments of crops and pollinator manage-

ment which can be applied to new cropsnew varieties new planting or croppingpractices Kevan (1989) has pointed outthat clear questions remain about thepollination requirements of fully half ofthe 40 crop species grown in CanadaThe situation is even more acute forThird World crop pollination (Kevan1984) Even for major plantation cropsan understanding of pollination has onlyrecently developed For example coco-nut (Cocos nucifera L) pollination maybe by wind or insects or both (Pouvreau1984a) while oil palm has only recentlybeen recognized as being dependent oninsect pollination (Syed 1979 Kevan etal 1986)

Pollinators and their rewards

Coevolution has produced a mutual-ism between pollinators and floweringplants Insect pollinators have greatlyexpanded opportunities for genetic re-

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combination in plants a process whichis integrally related to angiosperm evo-lution adaptation and diversity In re-turn pollinating insects obtain nutrient-rich nectar and pollen

Nearly all pollinators take nectar fromflowers although not all flowers pro-duce nectar Nectar is a sugary liquidwith numerous minor components(Baker and Baker 1983) and servesmostly as carbohydrate fuel for flight inpollinators Not all floral nectars areequally useful to pollinators and manyspecial relationships are known in nature(Baker and Baker 1983) Some polli-nators notably honeybees bumblebeesand some other tropical bees gather nec-tar and return with it to their nests(hives) where it is cured made intohoney and stored Thus honeybees canbe thought of as sophisticated biome-chanical micromanipulators whichgather and exploit a resource-nectar-which would otherwise be unharvestableand convert it into human-usable prod-ucts By channeling and encouragingtheir foraging and colonizing behaviorbees have been made to serve agricultureboth directly in the production ofhoney and indirectly via pollination ofdependent crops

From the perspective of honeybeesbumblebees and a few other bees honeyrepresents the energy store for lastingout the winter or for shorter periods ofbad weather or floral dearth Towardstheir own sustenance and that of theirbrood bees also gather pollen a highlynutritious substance which is rich in pro-teins carbohydrates lipids vitaminsand minerals (Stanley and Linskens1974) Pollen together with nectar andnutritive glandular secretions from thebees is fed to larval bees and providestheir entire nutritional requirements un-til they metamorphose to become adultsAs with nectar not all pollen is equallyvaluable to bees Conifer pollen for ex-ample has little nutritive value and isnot usually taken by bees

Solitary (not colony building) beesbuild their own nests which are com-prised of cells provisioned with a loaf ofpollen and nectar upon which they layan egg The bees seal up the individualcells the egg hatches and the larva de-velops while feeding on the loaf and

eventually metamorphoses to become anadult Other pollinators such as flies(Diptera) moths and butterflies (Lepi-doptera) and beetles (Coleoptera) in-gest nectar pollen or both for their ownnutrition and for the maturation of theirgonads The females do not contributeprovisions other than what they haveplaced in the yolk of the egg

The diversity and value ofpollinators

Bees

A huge proportion of the worlds in-sect fauna visits flowers for sustenancebut not all are efficient pollinators Al-though bees are recognized as beingamong the most important pollinatorsin almost all ecosystems where flowersoccur (excluding for example marinesea grasses) their precise roles in pol-lination are not well documented Some30000 species of bees are known to sci-ence ranging in size from tropical giantsof nearly 8 cm long to minute sweat beesof about 2 mm in length About 190species of bees have been associated withpollination of lowbush blueberry innortheastern North America alone (Fin-namore and Neary 1978)

Honeybees

Despite the array of bees potentiallyavailable only a few species includinghoneybees have been placed under someform of management The presence of aviable honeybee industry in NorthAmerica attests to the adaptation of thiseusocial species to modern agricultureIn Europe and North America the Eu-ropean honeybee (Apis mellifera ssp)dominates while in South and CentralAmerica the Africanized honeybee(Apis mellifera x scutellata) or so-calledkiller bee has displaced the Europeanbee in its inexorable spread (Needhamet al 1987 Morrison 1989) In Africavarious native races of A mellifera arepollinators although there is little man-agement of these honeybees for that pur-pose In Asia the Asiatic hive bee Acerana Fabr occurs in the wild and is

used for beekeeping and pollinationOther wild honeybees the giant or rockhoneybee A dorsata Fabr and the littlehoneybee A florea Fabr are importantin tropical and subtropical Asia Euro-pean bees have been introduced intoAsia with some success (FAO 1984)especially in temperate areas In Aus-tralia and New Zealand European ho-neybees were introduced in the early1800s for honey production and polli-nation Honeybees are used primarily forhoney production although in placessuch as Africa and South America waxproduction is also of great importance(Free 1982) In only a few special placessuch as the Okanagan Valley of BritishColumbia and in parts of California ispollination the main motivation forkeeping honeybees Thus most honey-bees act as pollinators as a side benefitto their honey production

Economic analyses of the value of in-sect pollination to agriculture hasstressed the importance of honeybees(Eckert and Shaw 1960 Levin 19841986 OGrady 1987 Robinson et al1989 Winston and Scott 1984) even inthe context of wildlife habitat (Barclayand Moffett 1984) Although somestudies (especially OGrady 1987 Rob-inson et al 1989) attempt to ascribe apercentage of crop production to the pol-linating activity of honeybees the pro-portions used are based on opinions orestimates by apiculturalists rather thanon rigorously gathered data The mostaccepted estimates indicate that honey-bees account for at least 80 percent ofall insect pollination (Robinson et al1989) Another recent analysis (againbased on estimates) suggests that thevalue of honeybees is much lower thanthat suggested above (E E Southwick1989 personal communication)

The Province of Ontario serves as agood example of how pollination takesplace in most agricultural settings In1988 there were 5400 beekeepers and115000 colonies registered in OntarioOf these only 280 beekeepers had morethan 100 colonies and could be catego-rized as commercial beekeepers Ofthose only 20 managed their bees forpollination and provided a commercialservice to crop growers (McRory per-sonal communication)

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Thus it can be appreciated that mostcrop pollination by honeybees is a freeservice done by a widely scattered pop-ulation of honeybees in hives managedby hobbyists and by commercial honeyproducers

Beekeeping in Ontario in Canadaand in North America generally is inserious financial trouble Commercialbeekeepers are finding it increasingly dif-ficult to make a profit because of thevery low price of honey on domestic andworld markets (ca US$080Ag in 1988)vs the estimated cost of production atca US$120Ag in Ontario (D McRorypersonal communication) The value ofother hive products and pollination isvery small Mechanization in beekeepinghas helped increase efficiency over theyears (Free 1982) but beekeeping is alabour-intensive operation and the taskof attending hives is not amenable tomachine operation Consequently thenumber of commercial beekeepers andhives in Canada has declined over thelast two decades

Beekeeping in Canada is now threat-ened by two extremely serious diseasesof honeybees which are prevalent in theUSA (Needham et al 1987 Morrison1989) These diseases which are causedby the trachael mite Acarapis woodi andby the ectoparasitic mite of bee broodand adults Varroa jacobsoni afflict onlyhoneybees Both parasitic mites debili-tate the honeybees they infect so thathives dwindle in strength and die outAlthough control measures for these dis-eases are being developed and are avail-able in other countries they add to thecomplexity and cost of beekeeping Themite diseases will enter Canada becauseof the natural movement of infected beescrossing the CanadaUS border and bythe actions of irresponsible beekeepersimporting bees from abroad Once thathappens beekeeping will necessarily be-come a more sophisticated operationthan it has been in the past The runningof efficient commercial operations willcost yet more up to US$700hive peryear in supplies alone (D McRory per-sonal communication) The cost of pol-linator services as they become scarcerand more needed will rise

Compounding this set of problemswill be the likely decline in the number

of hobby beekeepers who will abandonor reduce their activity because of theadditional labor and chemical inputsneeded to control the parasitic mitesThus because of both higher costs andlesser numbers of operators the free pol-lination service now provided by honey-bees will likely be severely reduced

Other bees

Although honeybees are recognized asthe most valuable pollinators in agri-culture worldwide there are other no-teworthy contributors For example thealkali bee Nomia melanderi Cockerellwas among the first of the solitary beesto be used for pollination of alfalfa inthe western USA Alkali bees burrowinto the soil and make subterranean cellswhich are provisioned with pollen andnectar Artificial bee beds are used tomaintain these bees

The alfalfa leafcutting bee Megachilerotundata Fabr is now widely used foralfalfa pollination It naturally nests intunnels previously made by woodboringinsects in fence posts and trees Its cellsare made of pieces of leaf moulded intoa minute thimble (ca 1 cm long) Leaf-cutting bees are easy to manage and setout for alfalfa pollination (Richards1984) requiring less attention than dohoneybees but tend to prefer warmsunny weather Alkali bees require evenless management merely the establish-ment and protection of a special bed ofsoil in which they can nest (Stephen1960) Both the alfalfa leafcutting beeand the alkali bee are better than ho-neybees at tripping the complex floralmechanism which effects pollinationHoneybees tend to remove nectar with-out tripping and hence without polli-nating the flowers Progress is beingmade in selecting alfalfa leafcutting beeswhich will work under the cooler win-dier and cloudier weather which typifiesnorthern areas of alfalfa production inCanada (Pankiw 1987)

The orchard bees Osmia spp alsonest in tunnels in wood but make theircells with mud For both Megachile andOsmia artificial nesting tunnels can bemanipulated moved and stored (Tor-chio 1987) Orchard bees have beenused for commercial pollination in var-

ious parts of the world most particularlyin Japan where orchard bee culture iswell developed By comparison with ho-neybees orchard bees are far superiorfor apple pollination It has been esti-mated that 356 female bees are enoughto pollinate an acre of an apple orchardwhile several hives each containing tensof thousands of honeybees would beneeded to achieve the same result (Tor-chio 1987) Furthermore orchard beeswill forage during the orchard treebloom when the weather is cool windycloudy and damp conditions which ho-neybees eschew Orchard bees also for-age widely throughout the orchardrather than at a single tree or group oftrees as do honeybees The use of or-chard bees in pollination will probablyincrease as their value is recognized andas the cost of honeybees keeps rising

Bumblebees Bombus spp have alsobeen used for crop pollination but areexpensive to manage and pose problemsin rearing These factors restrict theiruse to very high value crops (Plowrightand Laverty 1987) Bumblebees aremostly found in temperate climatesThey are eusocial like honeybees butwith smaller rather less structured nestsmostly underground in abandonedmammal burrows The nests last but oneyear for most species Inseminatedqueens are the final survivors which ov-erwinter for the next years generationBumblebees are the pollinators of choicefor red clover (Trifolium pratense L)and cranberries (Vaccinium macrocar-pon Ait) They have been introducedinto New Zealand (Dunning 1886) andChile (Arretz and Macfarlene 1986) forred clover pollination In New Zealandthey are also being used to pollinate ki-wifruit (Actinidia chinensis Planch)(Pomeroy 1988) Bumblebees are prob-ably very important pollinators of manycrops including alfalfa fruit trees andsmall berries but they have not beensufficiently recognized as such Pou-vreau (1984b) provides an excellent re-view of the potential for bumblebees aspollinators Recent developments inHolland indicate an important role forthese bees in greenhouse pollination es-pecially of tomatoes (van Heemert per-sonal communication)

Carpenter bees (Xylocopa spp) are

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mostly tropical and subtropical Theymay be excellent pollinators of vinecrops especially of passion fruit (Pas-siflora edulis Sims) (Bohart 1962) giantgranadilla (P quadrangularis L) kiwi-fruit various gourds and winged beans(Psophocarpus tetragonolobus (L) DC) but have not been the subject of muchresearch They bore into wood or rest inhollow stems both of which can be eas-ily provided in the settings where suchcrops are grown

Squash bees Peponapis spp and Xen-oglossa spp which are related to car-penter bees are more specialized butperhaps more manageable Squash beesare specific to squashes pumpkins andgourds One species of squash bee Pe-ponapis pruinosa (Say) has followed cul-tivation of Cucurbita pepo from thesouthwestern US to southern Canada(Kevan et al 1988) The bees nest inunderground burrows They become ac-tive at dawn visiting cucurbit flowersuntil about midday when the unisexualflowers close As a result they typicallystart to pollinate the crop before honey-bees are abroad and have finished by thetime honeybees are at their most activefrom midmorning on (Kevan et al1988) Squash bees could be kept in beebeds near farms specializing in thesecrops as is currently under test on avegetable farm in Ancaster Ontario(Kevan and Willis unpublished)

Other candidate pollinators amongthe native bees would include sunflowerbees (Eumegachile pugnata (Say)) (Par-ker and Frohlich 1985) blueberry bees(Habropoda laboriosa (Fabr)) (Sanchez1989) and Osmia ribifloris Michener(Torchio 1990ab)

Other insect pollinators

Perhaps the most valuable specialtypollinator in terms of world trade hasbeen the oil palm weevil Elaeidobius ka-merunicus (Syed 1979 PORIM 1985Kevan et al 1986) Until recently ithad been assumed mistakenly as itturned out that oil palm was pollinatedby the wind Thus in southeast Asia oilpalms were either artificially pollinatedor pollination was left to the vagaries ofthe wind or other insects The carefulintroduction of the oil palm weevil from

its native West Africa into Malaysia in1981 has saved millions of dollars in la-bor as well as improving crop perform-ance (PORIM 1985 Kevan et al1986)

Cocoa (Theobroma cacao L) has spe-cialty pollinators as well but these arewidespread non-biting midges Forcipo-myia spp which breed in rotting veg-etation (Pouvreau 1984a) Thus in mostplaces there is a resident population ofmidges for pollination However over-cleanliness in cocoa plantations can re-sult in crop failures (Winder 1977) Ef-forts are now made to encourage midgepopulations by providing sections of rot-ting palm trunks in which they canbreed (Ismail and Ibrahim 1986)

Losses of managed andwild pollinators

The likelihood of diminished popu-lations of honeybees to pollinate com-mercial crops has focused attention onalternative pollinators both managedand wild The lack of adequate numbersof wild bees for crop pollination can beattributed to two interrelated processes(1) direct poisoning by insecticides and(2) destruction of habitat for pollinators

Insecticide-based losses

The devastating effects of insecticideson honeybees are well known (Johansen1977 NRCC 1981) but the costs ofthese effects have not been well docu-mented The economic implications ofthe loss of pollinators to agriculture andto natural ecosystems may be envisionedfrom several case studies involving in-secticides In New Brunswick the in-secticide used to control a forest pestthe spruce budworm (Choristoneura fu-miferana Clem) was changed fromDDT(dichlorodiphenyltrichloroethane)to the organophosphorus compoundfenitrothion (00-dimethyl 0-4-nitro-m-tolyl phosphorothioate) which is highlytoxic to bees in 1970 In blueberry fieldsnear tracts of treated forest the resultingdemise of blueberry pollinators has beenwell documented (Kevan and LaBerge1979) and was cause for alarm becauseof the dependence of fruitset in lowbush

blueberry on insect pollinators A de-cline of 665 tonnesyear in blueberryproduction in New Brunswick coincidedwith the period during which fenitro-thion was used and when its aftereffectscould be assumed to be operating(Kevan and Plowright 1989) despite ef-forts of blueberry growers to circumventthe loss of native bees by importing ho-neybees for pollination The demise ofnatural pollinators in the forests of NewBrunswick Quebec and Ontario hasalso been documented to be associatedwith fenitrothion and other insecticideapplications (Kevan and Plowright1989)

Another example is for alkali beeswhere inadvertent pesticide poisoning inWashington was estimated to have cost$287000 in lost alfalfa seed productionin 1973 (Johansen 1977) More recentlythe loss of honeybees caused by infectionby Varroa mites in Israel is thought tohave resulted in losses of the cantaloupecrop (Cucumis melo L) (D Eisikowitchpersonal communication)

Habitat-based losses

The consequences of habitat disrup-tion on populations of pollinators wouldwarrant a greater research emphasisFor example the trend in agriculture tolarge-field monoculture has eliminatedlarge areas of wildlife habitat and sorelyaffected pollinator populations In Brit-ain for example a reduction in the pop-ulation of bumblebees has beenattributed to changes in land use Wil-liams (1986) attributes declines in theabundance and diversity of British bum-blebees to increased amounts of culti-vation alteration of drainage and itsconsequent effect on the flora of bum-blebee forage removal of rough land andhedges at field margins and uniformityof crop plants and perhaps climaticchange Peters (1972) also consideredsome of these effects as causing declinesin populations of bumblebees in Ger-many

In Canada the centermost plants inlarge-scale alfalfa fields have been re-ported to be poorly pollinated with pro-duction dropping from 1000 kgha to150 kgha in 4 to 10 years of extensive

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land clearing The elimination of landfor nesting sites of native pollinators hasbeen cited as the cause (Stephen 1955)Benedek (1972) discusses the negativeimpact of weed control on populationsof wild pollinators of alfalfa and of otherflower visiting insects in Hungary

Other crops which may suffer becauseof large-tract monoculture are cranber-ries (Kevan et al 1983) and various fruitand nut crops such as cocoa cashews(Anacardium occidentale L) NorthAmerican paw paw (Asimina triloba (L)Dunal) (Kevan unpublished) Weedcontrol on blueberry lands in Maine isnow being considered as a main causefor the paucity of native bee pollinators(E Osgoode personal communication)

Meeting the needs of croppollination in the future

Agriculture requires a secure sourceof reliable pollinators As we have notedthe principles of honeybee use and man-agement are well known and honeybeesare valued for their honey wax andother hive products However we havealso argued that honeybees do not sufficefor all crops or under all environmentalconditions and that a variety of factorsare pending which may unsettle andmodify the status quo From this anal-ysis it is concluded that a more com-prehensive strategy for management ofcrop pollination will be needed in thefuture

A variety of pollinators ranging fromhighly managed to wild will provide lat-itude and security in crop pollinationBeekeeping with honeybees must be en-couraged starting with a recognition ofthe problems and values of beekeepingTo ensure reliable pollination growerswill have to be more willing to pay forpollination services because the price ofhoney is set by market forces beyondnational borders However honeybeesshould not be perceived as the ultimateand only pollinator for agriculture

Examples of reliable alternative pol-linators for specific crops are known foralfalfa oil palm and cocoa as discussedabove Promising alternative pollinatorsfor other crops include orchard beessunflower bees blueberry bees squash

bees and bumblebees (Torchio 1987Kevan et al 1988) The huge diversityof wild pollinators indicates that theabove examples are only the very tip ofa highly valuable if unrecognizedmother lode

To manage encourage or conservealternative pollinators requires a basicunderstanding of their biology and ecol-ogy Nesting habitat must be providedwhether as a soil bed of a more or lessspecial nature or as stumps of trees andlogs or as rodent burrows for bumble-bees At present too little is known todefine and recommend the specific hab-itat requirements of most bees Howeverproviding relatively undisturbed fieldedges hedgerows fencelines wind-breaks woodlots ponds streams andstone piles would be expected to assistpollinators (Stephen 1955 Williams1986) Provision of artificial nestingsites such as wooden blocks or log endswith holes bored into them cavities forbumblebees and protected or managedbeds of soil would facilitate pollinatormanagement

The pollinators which are enticed tooccupy habitats need alternate sourcesof forage when crops are not in bloomFor example the annual cycle of a bum-blebee colony involves overwintering bythe queen who establishes and rears thefirst cohort of worker bumblebees byherself in the spring Eggs are then laidin the summer after which the colonydeclines and all but the queens perishClearly a persistent bumblebee colonyrequires sustenance throughout springsummer and fall

Many solitary bees have relativelyshort lifespans which may not coincideexactly with the timing of a specific cropbloom Thus if a pollinator emerges asan adult slightly before a crop is inflower or if the blooming period of thecrop is shorter than the bee lifespan ad-ditional floral resources are needed tosupport the bees Other pollinators mayhave two or more generations per yearThus they may be pollinators at onetime and forage on crops but at othertimes the generation of pollinators re-quires other sources of pollen andornectar

To accommodate the various needs ofbee populations forage in the form of

flowering weeds wild herbaceousplants shrubs vines and trees must beavailable Such plants can be allowed tothrive with little or no management ormay be specially encouraged or sown Anumber of examples serve to illustratethe principle although individual sitesand habitats will have different require-ments Willow (Salix spp) for exampleis an excellent source of nectar and pol-len in early spring for a wide variety ofpollinating insects Marjoram (Ori-ganum spp) and clovers have longblooming periods and are a good sourceof nectar during the summer as well asproviding ground cover Sweetclover(Melilotus spp) ft a valued bee crop insummer and fall asters (Aster spp) areproductive pollinator forage late in thesummer In addition a variety of othershrubs and trees may be used as wind-breaks and as pollinator forage includ-ing Caragana spp Prunus spp Rosaspp and Viburnum spp For detaileddocumentation of plants which are goodsources of nectar and pollen in Canadaand the USA see Ramsay (1987) andPellett (1976)

Land use changes andpollinator management

Native pollinator habitat can be en-hanced by local initiatives on privatelands including thoughtful managementof non-cultivated patches of ground asnoted above Public policy can also assistthrough the setting aside of municipaland regional parks or protected areas forwildlife flora and fauna For examplein the USSR a park has been set asidefor bumblebees reflecting a degree ofdedication that would be useful in areasparticularly unique for or especially fa-vorable to bumblebees other bees or forother rare or special plants and polli-nators

Along the edges of arable land con-servation authorities could facilitateplanting of hedges and fence rows tospecies (see above) which would en-courage pollinator populations The ex-tensive use of conifers on managedconservation areas should be discour-aged in favor of a strategically selectedmixture of species For land rehabilita-

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tion along eroded streambanks lake-shores landfills and other disturbedsites a variety of herbaceous as well asshrubby and woody species would bepreferable to the current practice ofmostly hybrid poplars maples and con-ifers Greater diversity would also pro-vide more suitable habitat for small birdsand mammals as well as crop pollina-tors

As already demonstrated in Ontariobirdsfoot trefoil Lotus corniculatus L)and crownvetch Coronilla varia L) arerepresentative of good cover and bee for-age crops for roadside and slope stabi-lization In about 1974 a stretch ofroadside in Ontario was planted to ho-neybee forage (G F Townsend per-sonal communication) but the presentstatus of this area is unknown R Shuel(personal communication) suggests thatabout 40 kg of honey could be harvestedfrom 16 km of florally rich countryroadside in Ontario Thus areas such asroadsides which are now managed tolimit or inhibit vegetation could be man-aged to enhance selected vegetationtypes with direct as well as indirect eco-nomic benefits

Where possible roadsides and high-way verges should be mowed rather thanchemically treated to keep vegetationlow enough to ensure visibility for mo-torists (eg in Garafraxa Township On-tario) Noxious weeds in Ontario aredesignated by the Ontario Weed ControlAct (1974) which states that Everyperson in possession of land shall destroyall noxious weeds thereon Some nox-ious weeds are excellent nectar and pol-len plants including thistles Cirsiumspp) milkweed Asclepias syriaca L)chicory Cichorium intybus L) androcket Barbarea spp) The practicalityof the Act notwithstanding these weedshave considerable value in supportingthe lives of flower visiting insects es-pecially pollinators (Benedek 1972)Weed control has been cause for bee-keepers concerns about reduced foragefor bees in various parts of the world(Crane 1981 Crane and Walker 1983)

Recent reviews (Altieri and Whit-comb 1979 Altieri and Letourneau1982 Altieri and Schmidt 1985 1986Andow 1988) document that the inci-dence of pest insects is sometimes lower

and of predators and parasitoids can behigher on crop plants close to weeds oruncultivated areas These studies men-tion specifically the importance of nectarand pollen sources for beneficial biocon-trol insects but do not consider the cen-tral process of pollination for cropproduction Batra (1982) briefly notesthe benefits of polyculture and weeds topollinators and other beneficial insectsbut indicates that these benefits may beoffset by the provision of alternativehosts and hibernaculae for pests How-ever Van Emden and Williams (1974)indicated that insect pest movement intocrops often can be attributed to the ab-sence rather than to the presence ofother plants near the crops Clearlythere is need for recognition of both pol-linators and other beneficial insects inassessing the costs and benefits of weedsand uncultivated land in cropping sys-tems (Kevan 1986)

A policy of providing and managingdiverse pollinator habitats will aid in ag-ricultural productivity as well as en-hancing the beauty of the rurallandscape with colorful flowering spe-cies Management of these habitats in-cluding roadsides rights of way forpowerlines and railways fencelineshedgerows woodlots and streambankswith minimal use of chemicals will helprestore some ecological diversity to po-tentially monotonous and visually sterileagricultural landscapes

Conclusions

Rather than being an enemy to beovercome and conquered nature can bean active and beneficial contributor tothe practice of agriculture Pollinatorsare a pivotal link in the natural economyof the earth including agriculture andother human activities Yet the directeconomic importance of insect mediatedcrop pollination and of the incalculablevalue of pollination in natural systemsby honeybees and more critically bynative pollinators has been overlookedand undervalued At present unfavor-able economics parasitic mites and Af-rican bees threaten the extent anddistribution of the honeybee industry inNorth America These impending dan-gers expose the critical vulnerability of

pollination-dependent crops in the ab-sence of reliable populations of alter-native pollinators which havethemselves been reduced by agriculturalpractices A wide array of insects someof which have been employed as spe-cialty pollinators is available to aug-ment and reinforce the honeybeeindustry in commercial-scale crop pol-lination However only a handful havebeen investigated and fewer than 10 havebeen studied thoroughly enough to be inuse for commercial crops The lack ofinformation on other candidate speciesstems more from overdependence on ho-neybees rather than on intrinsically in-surmountable difficulties in themanagement of other pollinators Stud-ies on alternative pollinators are ur-gently needed

The explicit encouragement of man-aged and native pollinators by limitedand strategic use of biocides by plannedhabitat development and maintenanceand by field dimensions consistent withpollinator flight ranges must be an in-tegral part of newer approaches to foodproduction through sustainable agricul-ture Enlightened habitat managementwhether through personal initiatives onprivately owned land or by developmentof ecologically responsive policies onpublic lands will enhance populationsof biocontrol agents and native polli-nators to the benefit of agriculture as awhole

Acknowledgments We are grateful to D McRoryProvincial Apiarist for Ontario for providing informationon beekeeping to D Eisikowitch Tel Aviv Universityfor his discussions on Varroa in Israel and to E OsgoodeUniversity of Maine Orono E E Southwick SUNYBrockport R Shuel University of Guelph and the lateG Townsend University of Guelph

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RESOURCES

Alternatives in Pest Managementfrom the University of Illinois Coop-erative Extension Service now in-cludes four publications MicrobialInsecticides (C-1295 $1) Botanical In-secticides and Insecticidal Soaps (C-1296 $2) Insect Attractants and Traps(C-1297 $2) and Beneficial Insectsand Mites (C-1298 $2) Request by ti-tle and number from the University ofIllinois Office of Agricultural Com-munications and Education 69-02Mumford Hall 1301 West GregoryDrive Urbana IL 61801

The Cost and Return Estimator acomputer program from the US SoilConservation Service helps land userscompare their current methods withmore sustainable farming systemsContact county SCS offices for moreinformation

GreenPrints a literary gardeningnewsletter focuses on inspirationalwriting for small growers $10 for fourquarterly issues Contact GreenPrintsPO Box 1355 Fairview NC 28730

Agriculture Diversification Series14 publications from Iowa State Uni-versity Extension includes RabbitsBeekeeping Raspberries Straw-berries Broccoli and CauliflowerSod Production FuelwoodSweet Corn Snap Beans MapleSyrup Christmas Trees AngoraGoats Muskmelon and Peren-nials Copies are free from Publica-tions Distribution Printing andPublications Iowa State UniversityAmes IA 50011 or Iowa county ex-tension offices

Synergy a magazine from Saskatch-ewan Canada carries news articlesand some research related to organicfarming in Canada The Spring 1990issue (Vol 2 No 2) has an article byStewart Brandt of Agriculture CanadaExperimental Farm on Indian headlentil as a green manure substitute forsummer fallow Subscriptions are $12year (Canadian) from Synergy Box9859 Saskatoon Sask S7K 7Z2 Can-ada

Farming With Fewer Chemicals AFarmer-to-Farmer Directory describesthe operations of 39 no- or low-chem-ical Iowa farmers It is $2 for farmers$7 for non-farmers from the Iowa Cit-izens for Community Improvement1607 East Grand Avenue Des MoinesIA 50316

Farmer Participation in Researchfor Sustainable Agriculture is a 102-page report from the 1989 conferenceof that title Copies are $575 fromConference Report ATTRA PO Box3657 Fayetteville AR 72702

1990 Organic Wholesalers Direc-tory and Yearbook lists over 400grower-wholesalers distributors andfarm suppliers in North America andprovides a guide to certification andsupport groups Copies are $28 post-paid (California residents add $156tax) from the California Action Net-work PO Box 464 Davis CA 95617

1990 Organic Certification Hand-book from the California Certified Or-ganic Farmers (CCOF) is a newlyrevised 42-page document that in-cludes lists of acceptable materialsCopies are $10 from CCOF PO Box8136 Santa Cruz CA 95061-8136

Organic Certification (SRB-90-04)is a USDA bibliography on the topicdated January 1990 Single copies arefree with a self-addressed label sent tothe Reference Branch Room 111 Na-tional Agricultural Library BeltsvilleMD 20705

Environmentally Sound Small ScaleAgricultural Projects a revised editionprepared by Miguel Altieri covers theplanning process for a more sustainablesmall-scale agriculture with a ThirdWorld perspective The manual in-cludes ecological concepts and otherfactors related to designing environ-mentally sound projects in the areas ofwater supply and management nu-trient management soil conservationpest management and agroforestrysystems For information contactVITA Publication Services PO Box12028 Arlington VA 22209

22 American Journal of Alternative Agriculture

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