Ghanim, M., Department of Entomology, Institute of Plant Protection, The Volcani Centre, Bet Dagan 50250, Israel
Kontsedalov, S., Department of Entomology, Institute of Plant Protection, The Volcani Centre, Bet Dagan 50250, Israel

BACKGROUND: The presence of symbiotic microorganisms may influence an insect's ability to tolerate natural and artificial stress agents such as insecticides. The authors have previously shown that Rickettsia in the B biotype of the whitefly Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) increases this insect's susceptibility to several insecticidal compounds. This communication reports a comparison of the susceptibilities of three isofemale strains of the Q biotype of B. tabaci harbouring different bacterialcomplements tomajor insecticides from different chemicalgroups: onestrain harbouredonly Arsenophonus, one harboured Rickettsia and Arsenophonus and one harboured Arsenophonus and Wolbachia. RESULTS:The presence of different symbiont combinations in the three strains had a significant influence on their susceptibility to most of the insecticides tested. Thiamethoxam, imidacloprid, pyriproxyfen and spiromesifen had a significant influence on strains that had the double infections Rickettsia-Arsenophonus and Wolbachia-Arsenophonus, which also carried higher amounts of symbionts as assessed by quantitative real-time PCR. No significant differences in mortality rates were observed when the tested strains were treated with diafenthiuron. CONCLUSION: The results suggest a correlation between the presence of high bacterial densities in B. tabaci and the insect's ability to detoxify toxic compounds such as insecticides. © 2009 Society of Chemical Industry.