Imidacloprid modulates spider mite endosymbiont Wolbachia leading to its resurgence

The twospotted spider mite (TSSM) Tetranychus urticae Koch (Acari: Tetranychidae), has been recognized as the most important arthropod pest. Imidacloprid, a neonicotinoid insecticide, increases the fecundity of mite populations. In the present study, a significant increase in mite numbers and mite egg production was observed at different days when mites were fed on imidacloprid treated leaves than control. In addition it was observed that the mite populations which were fed on imidacloprid treated leaves were more male biased i.e. the ratio of male:female at 30 days was 40:60 and at 50 days it was 25:75. As endosymbionts particularly Wolbachia bacteria are known to cause alterations in reproductive phenotype of hosts including TSSM, 16S sequencing was done in bacterial isolates which confirmed Wolbachia spp. infection. BacLight live-dead staining and real-time PCR were performed for Wolbachia quantification using PCR primer pair of wsp, which confirmed of higher number in mites obtained from imidacloprid treated plants versus control. Though, imidacloprid showed only a slight extended viability of in vitro cultures of Wolbachia isolates from these mites. Interestingly, a significant increase in Wolbachia viability as well as fecundity of mites was observed when they were fed on imidacloprid treated leaves. This increase was however not found in mites fed on antibiotic tetracycline treated leaves. Imidacloprid triggered mite fecundity can be clearly ascribed to increase in endosymbiont wolbachia.