Proceeduiq« of the 7th lniernational Worhng Conference on Stored-product Proiectuni - Yolume 2

Evaluation of Bacillus thuringiensis emulsion YW-l forcontrolling coleopteran pests infesting stored product

Zhang Hongyu", Wan Kaiyuan", Deng Wangxr , Yang Changju' and Yu zmnr'

Abstract

Insecticidal activity of B. tnuruunensu. emulsion YW-1against adults of Lesser gram borer, Rhszopertha domm icaFab ; Maize weevil, Sitophilus zeomuus Motschulsky;Rust-red flour beetle, Tribolium. castaneU'm(Herbst); Flatgrain beetle, Cryptolestes muiuies (Oliver ), Saw-toothedgram beetle, Oryzaephilus suruuimensis (L.) and thelarva of Rust-red flour beetle were evaluated through nuxingB. thuringiensis emulsion with diet. The results showedthat the corrected mortality to adults of Rust-red flourbeetle, Flat gram beetle, Saw-toothed gram beetle and thelarva of Rust-red flour beetle were 43.33%, 40%, 43.33%and 68.42 % respectively at the dosage of 50ul/g diet, whilethe corrected mortality to Maize weevil and lesser gramborer were 19.23% and 91.38% at the dosage of 4.5ul/gdiet. So B. th/uruunensis emulsion YW-1was effective tocontrol lesser gram borer at the dosage of 4.5ul/g diet, andlesser grain borer was selected for further toxicity tests toevaluate LC50• The results showed that Its LC50 was 1.51 ul/g diet and suggested that B. thurinqietun» could bepotential biological control agents for certain stored productsbeetles such as lesser gram borer

Introduction

Coleopteran pests are a kind of most Important pest, andcause a senous loss of stored product Control of coleopteranpests ISstill depended on the use of chemical msecticide. Inrecent years, pest resistance and environmental concernsmake chemical insecticide such as contact insecticide andfumigants be challenged (Zhang Hongyu et al. , 1995). Thebiological control including microbial control IS a part ofmtegrated pest management (IPM), and a kmd of safelyecologIcal control. Research on blOlogical control hasincreased steadily since the early 1970s.Bacillus thuringwnsis ISa spore-formmg baCillusand IS

I Department of Plant ProtectIon, Huazhong Agncultural UmversIty,Wuhan 430070 P R Chma

2 Department of MIcrobial Science and Technology HuazhongAgncultural Umverslty, Wuhan 430070, P R Chma

distmguished from other bacillus by ItS ability to produce aendogenous crystals dunng sporulation. Those crystalproteins from many B tliuruunensu: strams were toxic tolepidopteran pests (Zhang Hongyu et aI, 1997).Preparations of those B. thuringw'rU3?'s have beeneffectively applied against stored-product moths(McGaughey 1976,1978). Although coleopteran-toxic Bthuringiensis strains such as B. thuruunensis subsptenebronis were Isolated and were used to control stored-product beetles (Mummigatti et al. , 1994; Zhang Hongyu etal , 1998), lacking highly tOXICstram IS still a lirrut factorto control coleopteran pests effectively with B.thurmqiensis formulation.ThIS study was done to evaluate control effectiveness of

B. th.urmqiensu: emulsion YW-1 against stored-productbeetles.

Materials and Methods

Origin of insect populations

All insect populations tested m this expenment wereobtained as laboratory colonies from Lab. of stored-productand urban msects. Huazhong Agricultural University. Table1 lists medra and physical condiuons for msects cultunng andbioassay as descnbed by Hames.

Bioassay

To determme the relative susceptibilities of those beetles,we suspended YW-1, an emulsion formulation of the spore-S-endotoxin complex of B. thiuruunensis (approximately 1.2x 1010 spores/ml) m water at a rate calculated to producethe concentration desired The suspensions were thoroughlyincorporated into insect diets at a rate of lOml/20g diet.Samples WIth 90% corrected mortahty at prehminary

screening tests were selected to evaluate LC50 values Wesuspended YW-1m water at a rate calculated to produce thehIghest concentratlOn deSIred, then senal1 2 dIlutions wereused to produce 5 concentrations of the formulatlOn. ThesuspenSIon was incorporated mto dIet accordmg to themethod at prelimmary screening tests Each blOassaywasrephcated 3 times, dIet samples were divided into 3rephcations of ca 33g each 30 lO-day adults or 2 - 3-daylarva of msect tested were added to each jar The jars wereheld at about 28 ± 2°Cand 60 -70% rh condItions. Mortahty

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Proceedings of the 7 th Internatwnal Worhng Conference on Stored-product Protection - Volume 2

was recorded after 3, 7, 12 and 20 days Mortahty m thetreated sample was corrected by that m control WIth theAbbott correcting Corrected mortahty at different dosage

Table 1. Physical conditions and media

then was compared by analysis of vanance and Duncan'smultiple range test FIt of the concentration-mortality hneto the data was evaluated usmg clu-square test.

msects medium (w /w) Temperaturef C ) relative hurrudt % )

Rhizopertha dominicaSitophilus zearnatSTribohum castaneumCryptolestes minutes

Oryzaeph1,lus surinaments

wheat

wheat

wholemeal flour and yeast] 12 1)

wheatfeed and rolled oats and yeast(S 5 1)wheatfeed and rolled oats and yeastt S 5 1)

28±2

28±2

28±2

28±2

28±2

60-70

60-70

60-70

60-70

60-70

Results and Discussion

Preliminary screening tests

Susceptibility of msects tested m this expenment to B.thuruuneneis formulation differed, m WhICh correctedmortahty was from 19.23 % to 91.38 % at the dosage used(table 2). Most beetles tested weren't susceptible, m whichcorrected mortahty was lower than 50%. Only lesser gramborer (Rhizopertha dominica ) was susceptible, in whichcorrected mortah ty was 91. 38 % at the dosage of 4. 5p.1Igdiet, So the B thunngiensis emulsion formulation hadcontrol effectiveness to different extent to those beetles, butcould not effectively control them at the dosages used exceptlesser gram borer.

Table 2. Stored-product beetle control usmg B.thuruunenei« emulsion YW-1

insectdosage

(p.lIg diet)

Averagecorrectedmortality( %)

adult of Rhizopertha dommicaadult of Sitophilus zearnaisadult of Tribolium. castaneumadult of Cryptolestes minutesadult of Oryzaephzlussuruuimenislarva of Tribolium. castaneum

4.5

4.5

50

50

50

50

91.38

19.23

43.33

40.00

43.33

68.42

Toxicity of YW-1 to lesser grain borer

Accordmg to the prehmmary screemng, lesser gram borerIS susceptible, and was selected for further toxicity tests toevaluate LCso values. The result is showed m table 3.3 daysafter treatment, control effectiveness was poor, m whichcorrected mortality of all concentration was lower than50%. Means of corrected mortality at the dosage of 2.251.13 and 0.28p.lIg dIet wasn't sIgmficantly different, andmeans of corrected mortahty at the dosage of 0.56, 0.28,

and ck didn't differ sigrnficantly at the 5% level. 7 daysafter treatment, means of corrected mortahty of any twoconcentration was sigruficantly different at the 0.05 level,and the corrected mortahty was higher than 90% at thedosage of 4. 5p.lIg diet, so Its bioassay data was SUIted toevaluate LCso. 12 to 20 days after treatment, means ofcorrected mortahty at the dosage of 4.50 to 2. 25p.lIg diet,corrected mortahty both higher than 90% At the dosage of0.56, 0.28p.lIg diet, the control wasn't SIgnificantlydifferent at the 5 % level.In addition, the means of corrected mortahty after 7 days

were smular to that of 12 to 20 days after treatment Itindicated 7 days were enough for evaluating tOXICItyof B.thurinqiensu: formulation to lesser gram borer.We analyzed the bioassay data of 7 days after treatment

usmg PROC probrt With the logistic option after correctingmortality m control With the Abbott Correction. Theregression equation of the concentration-mortalityrelationship was as follows:Y = 4 .5860 + 2.3263 z , r = 0 .9743Chi-square statistics showed no sigrnficant vanation of the

bioassay data from the logit regression model, indicatingthat the regression hnes were vahd representations of theconcentration-mortality relationship, the regressionequation was fit to calculate LCso value. LCso value was1.51p.lIg diet, and the fiducial limit was 1.24 - 1. 77p.lIgdiet at p = 0 .05.In this study, B. thunngiensis reduced stored-product

beetles infestmg to different extent, but most beetles testedcould not be effectively controlled at the dosage used.Lesser gram borer was more susceptible than the othertested, and B. thunngwnstS emulsion YW-1 couldeffectively control its mfestmg at the dosage of 4. 5p.lIg dietunder the laboratory condrtion So B thuruunenei«formulate could be potential biological control agents forcertam stored-product beetles such as lesser gram borer,and was regard as a part of IPM in stored-productprotection, particularly in the absence of more effectivetreatment.

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

Table 3. TOXIcity of B. thuruunenei« emulsion YW-l to Lesser gram borer.

treatment time Avg% corrected mortahty at the dosage of(days)

3

7

12

20

4.5O/ll/g 2.25/ll/g 1. 13rl/g 0.56rl/g 0.28/ll/g CKI

48.22a2 19.06b 18.54b 1 74c 3.26bc 1.79c

91.53a 57.82b 36.36c 10.68d 5.20de 1.7ge

100.00a 94.53a 45.36b 14.73c 1.63c 5.36c

100.00a 96.06a 50.13b 11. 78c 3.45c 12.50c

1 mortality of the control

2 Average corrected mortahty of any two concentration followed by the same letter are not sigrnficantly different at the 0 05 level by Duncan'smultiple range test

3 Means of three replications

Acknowledgments

This study was supported by International Foundation forScience.

References

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