Proceedings of the 7th Iniernatunial Working Conference on Stored-product Protection - Volume 2

Bionomics of Lariophagus( Hymenoptera: Pteromalidae )chinensis (Coeoptera: Bruchidae)

Deng WangxI1, Yang Shicheng'", LI Ruhm1

Abstract

In Wuhan, observations reveal that Lariophaqustustmqueiuius (Foorster) IS one of the major parasitoids inlarvae and pupae of Callosobruch.us clunensiei. andCallosobru,chus maculatus (Fabncius) in warehouses Thenatural parasitization rate IS 39.2 % The pupae overwmterm the tunnel of C. chineneis . The sex ratio of female tomale IS 7 3 At 25 ± 20°C and 75 ± 5% R H. The Iongevrtyof female and male adults IS 6.3 ± 1 days and 55.5 ± 1 daysrespectively The entire life CIrcle from egg hatch to adulttakes 16 to 20 days with an average of 18 days The adultscan emerge at day and night, but emergency at mghtoccupies 67.6 % of all Both female and male adults copulatemany times, and copulation and oviposition take placealternatively. Each female lays 15 to 19 eggs dunng ItSentire life span Each larva of C chinensis can beparasitized by 1 to 11 parasrte wasp After parasitized, theyoung mstar larvae of hosts turn mto drying, then to death,old mstar larvae can emerge to deformed adults be becauseof the disability to bore out of emergence hole Ldistuujuendus IS sensitive to Malathion The correctedmortality reaches to 100% after 24 hours at 10ppmconcentration Whereas It Isn't sensitive to K-Othnne, thecorrected mortality IS only 7 9% after 48 hours at 0 Ippmconcentration

Introduction

Caliosobruch.us ctunensis Lmne and Callosobrucliusmaculatus (Fabncius ) are Important msect pests thatmfestmg Chmese cowpea and Red bean In Wuhan,observations reveal that the larvae and pupae of the twopests were parasitized by several parasitoids, m whIch,Lariophagus dlstmguelldus take major responsIbIlIty for

1 Lab of Stored Product Insects, Huazhong Agncultural UmversIty,Wuhan, 430070, P R Chilla

Chillese Wuhan AnImal and Plant Quarantllle, Wuhan, 430070, PR Chilla

distinguendusparasitizing

( Foerster)Callosbruchus

the population amount. The biology and parasitism werestudied

Materials and Methods

Origin of insects

Lariopiuun,» dlStmguendus, Callosobruchus chinetunsand C maculatus were collected from Expenmental andTeachmg Ranch Warehouse of Huazhong AgnculturalUrnversity

Cultivation method

Group cultivation was carried on in Jars (500ml,0100mm) contammg 100g stenhzed Chmese cowpea With13.5% moisture content C chinensis and C maculaiusand L. distmguendus were raised in the Jars sealed Withcopper 70 # SIeves.

Bionomics of L. distinguendus

109 Chmese cowpea mfested by hatched eggs of C.chinensis and C. maculatus and 1 pair of latest emergedfemale and male adults of L disimquendus were mixedmto a 15 x 2cm cultivation tube for expenments.Oviposition, matmg behavior , life CIrcle and span of theadults were under observation. 20 cubes were set up and arandom samplmg was undertaken day by day Samples weresoaked and sectioned and data of parasitoid progress andparasrtoid density could be obtamed.

Observation of searching and parasitism

100g mfested and 100g non-mfested Chmese cowpea wereplaced mto open Jars respectively Each group contamed 6Jars and were arrayed alternatrvely m a row The cans weresealed WIth 70# SIeves. 240 L distiuquendus were placedmto the Jars Countmg and recordmg of the amount ofparaSI tOIds were undertaken every hour. ObservatIons oftheIr behaVIor and reactIOns were also carned out The Jarswere capped three days later. 30 days later the amount ofparasitOIds was calculated

Tests of sensitivities to pesticides

A solutIOn contammg 50% MalathIOn (proVided by Nmgbo

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Proceedmgs of the 7th Intenuuion«l Workmg Cml(erellce on Stored-pnxlud Protecuon - Volume 2

Pesticide Plant) at 10 and 15ppm concentration and 2 5lfcK-Othnne (provided by Roussel UCLAF) at 0.5 and Ippmconcentration respectively was applied to blend with Chmesecowpea The treated peas were exposed to air to dry up andthen were placed mto Jars 30 L distuutuendus adultsemerged 1 or 2 days before were mtroduced mto the Jarsthereafter Each procedure mentioned above was repeated 3times Clean water spray was used durmg the expenmentCalculation of dead parasitoids was earned out every 24 or 48hours. The corrected mortality was hence obtamed

Results and Analysis

Life history

In the natural environment, the parasitoid larvaeoverwmter m the tunnel dug by hosts m the peasOverwmtenng larvae emerge to adults m early Apnl andsubsequently bore out and complete matmg and ovipositionAt 25 ± 20°C, this CIrcle takes 16 to 20 days WIth an averageof 18 days The Iongevity of adults IS 2 to 7 days, 4 3 daysfor female and 3.1 days for male While fed WIth nutritionhquid WIth 10% bee honey, the longevity extendedobviously The longevity of female reached to 11.3 days andmale 8.2 days

Emergence

Before emergence, the parasitoid uses ItS mouth to biteout a Imm diameter hole at the thmnest part of the tunneldug by the hosts While emerging. Its head and upper bodybore out of the emergence hole first WIth swmg of ItS wholebody Its upper body then bends over ItS abdomen and pulls

out the rest of the body Even If a C eh inensts can beparasitized by over one parasite , It only makes oneemergence hole The adults can emerge day and night,however, 67.6% of all emergence IS at night. In the day,emergence happens most frequently m the mornmg

Mating and oviposition

Adults start matmg immediately after their emergencefrom peas While mating, male adult climbs upon femaleadult and hps the antenna of female adult With ItS mouthparts The female adult paralyzes soon The male mserts Itsperus mto the end of the female's abdomen. At this time thematmg adults gesture vertically The penis stays in thefemale's body for 1 to 5 seconds for each insertion, whichrepeats 3 to 5 times. Both female and male can mate manytimes Matmg and oviposition take place alternatively Theadults are movmg around to search for their hosts Thefemale adults could lay eggs immediately after matmgBefore oviposition, the female adults frequently search thehosts With therr antennae on the surface of the pea pIle.They stop movmg once they fmd the trace of C chinensism the peas They probe their ovipositors mto the pea andmove down vertically The eggs are laid on the surface oflarvae of C. eli Inensis or beside the wmg tips of the mothFemale adults can OVIPOSIteven WIthout matmg. The maleadult can thereafter emerge from the egg. Matmg alsohappens mside the pea If female and male co-exist m onetunnel, the female will not mate any longer after It bore outof the pea. The progeny could be both male and female Insome cases, the ratio of female IS relatively larger (Table1)

Table 1. Companson of sex ratio of progeny produced by solitary female and matmg of female and male

Form of female andmale in the tunnel

MatmgFemaleAdult

Femaleprogeny

Sex ratio(F M)

Co-existence

Solitary female

No more mating after emergmg of the hole

No matmg after emergmg out of the hole

10

10

67

67

4 43o 51

Reproduction ability

Autopsy was undertaken in the ovipositors of female adultsand It was found that there were 16 to 25 eggs WIth anaverage of 19.3 m each pregnant female adult However,each female adult only lays 15 to 19 eggs With an average of17 The sex ratio of the progeny IS 7 3.

Searching and parasitoid behavior

While L distmqueiulus was placed mto the Jarscontammg peas mfested and not-mfested by C chmensisrespectively, It was found that there were frequentsearchmg actiVIties occurnng m both Jars However, 3

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hours later, L distinquendus adults' actrvities were onlyfound m those mfested peas 30 days later, It was observedthat the progeny of L disiinquendu« was only found inmfested jars It indicated that L disimquendus found peasby ItS smell function and then only oviposrted after furtherdetection. The autopsy undertaken demonstrated that Ldisttnquetulus can parasitize dunng all life span of thelarvae and moths of C chi nensis It can also carry outcross-span, namely larvae-moth parasitization The parasitelarve feed on body lIqUId of the hosts When the host larvaeare parasItized by many L dlstuwuendus or the youngmstars are parasItized, the body of C. chmensU3 dnes upand only skms are remamed The dead body IS scattered

Proceedings of the 7th Internatwnal Working Conference on Stored-product Protection - Volu-me 2

with brown spots. Both heads and tails could not bedistinguished. When the host larvae are parasitized by smallamount of L. d1,Stmguendus or the older instars or mothsare parasitized, the host larvae can emerge to moths andhence the adults However, the emerged adults areunderdeveloped in smaller sizes, which are not able to boreout of the peas and will die in the end

Tests of sensitivity to pesticides

The test results of Malathion and K-Othnne can bereferred to in Table. 2 . The results indicate that L.distinguendus IS highly sensitive to Malathion. Thecorrected mortahty reached to 100% at lOppmconcentrationafter 24 hours' exposure. It IS not so sensitive to K-Othnne. The corrected mortality IS 4.2% at 1ppmconcentration after 24 hours and 14.2% after 48 hours.

Table 2. Anti-drug tests of L. disttnguendus' sensitivityto Malathion and K-Othrme.

TreatmentCorrected Mortality

after 24hours/ %)

CorrectedMortah ty after48 hours/ %)

lOppmMalathion

15ppmMalathion

o .5ppm K-Othrine1ppm K-Othrine

100

100

-2.7

4.2

7.9

14.2

Discussions

The natural parasitization rate of Lariophagus

d1,Stinguendus can reach to 39.2 % The population of C.chinensis can be effectively controlled if a certain amount ofLariophagus d1,Stinguendus IS introduced into thewarehouse. Once infested with C chtneneis , Chinesecowpeas WIll lose its economic value WIth empty hulls left.When Lariophagus d1,Stinguendus parasitizes C.dunensis , It only bites out Irnm diameter large hole m thepea. The hfe CIrcleof Lariopluuru» distinguendus IS shortand can produce two generations dunng one hfe circle of C.chnnensie . It has strong capability to search for hosts andthereafter oviposit mside the hosts. The cultivation methodIS not sophisncated. It IS feasible to apply Lariophagusdisttnguendus m control of C. chinensis If an efficientapproach to cultivate Larwphagus disimquendus in largeamount IS tabulated out

References

Gonen, -M: Kugler, -J . 1970. Notes on the biology ofLarwphagus d1,Stinguendus (forerster ) (Hymenoptera,Pteromahdae) as a parasite of Sitophslu» oryae (L )(Coloptera, Curcuhoidae) Isr-J-Entomol, 5: 133 - 140.Robert A. KIstler 1985. Host-age Structure and Parasitismin a Laboratory System of Two Hymenopterous Parasitoidsand Larvae of Zabrotes subfascwtus (Coleoptera:Bruchidae). Envrion Entomol. 14: 507 - 511.Yao Kang. 1986. Stored-product Pests and BeneficialInsects Beijing, China. p. 446.

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