The silverleaf whitefly, Bemisia tabaci (Gennadius, Hemiptera: Aleyrodidae), is a major threat to field and horticultural crops worldwide. Persistent use of insecticides for the management of this pest is a lingering problem. In the present study, the status of sensitivity of B. tabaci to two neonicotinoids, imidacloprid and thiamethoxam, was evaluated. The expression pattern of two cytochrome P450 (cyp) genes and changes in the relative amount of symbionts in insecticide-treated B. tabaci were also assessed. Quantitative PCR (qPCR) studies indicate that the CYP6CM1 and CYP6CX1 genes were always expressed higher in imidacloprid-treated whitefly, suggesting a correlation between gene expression and the insect’s ability to detoxify toxic compounds such as insecticides. In addition, the thiamethoxam-treated population harbored higher Portiera and lower Rickettsia titers, whereas the imidacloprid-treated population harbored more Rickettsia at different time intervals. Interestingly, we also examined that an increase in exposure to both the insecticides resulted in a reduction in the mutualistic partners from their insect host. These differential responses of endosymbionts to insecticide exposure imply the complex interactions among the symbionts inside the host insect. The results also provide a deeper understanding of the molecular mechanism of resistance development that might be useful for formulating effective management strategies to control B. tabaci by manipulating symbionts and detoxifying genes.
Bemisia tabaci (whitefly) is one of the most detrimental agricultural insect pests and vectors of many plant viruses distributed worldwide. Knowledge of the distribution patterns and insecticide resistance of this cryptic species is crucial for its management. In this study, genetic variation of mitochondrial cytochrome oxidase subunit 1 (MtCoI) gene of B. tabaci was analyzed followed by a study of the infection profile of various endosymbionts in 26 whitefly populations collected from West Bengal, India. Phylogenetic analysis revealed Asia I as the major cryptic species (65.38%), followed by Asia II 5, China 3, and Asia II 7, which were diversified into 20 different haplotypes. In addition to the primary endosymbiont (C. poriera), each of the four whitefly species showed a variable population of three secondary endosymbionts, majorly Arsenophonus with the highest infection rate (73.07%), followed by Wolbachia and Rickettsia. Further phylogenetic analyses revealed the presence of two subgroups of Arsenophonus, viz., A1 and A2, and one each in Wolbachia (W1) and Rickettsia (R3). Resistance to thiamethoxam, imidacloprid, and acetamiprid insecticides was analyzed for a clear picture of pesticide resistance status. The highest susceptibility was noted toward thiamethoxam (LC50 = 5.36 mg/L), followed by imidacloprid and acetamiprid. The whitefly population from Purulia and Hooghly districts bearing Asia II 7 and Asia II 5 cryptic species, respectively, shows maximum resistance. The differences in mean relative titer of four symbiotic bacteria among field populations varied considerably; however, a significant positive linear correlation was observed between the resistance level and relative titer of Arsenophonus and Wolbachia in the case of imidacloprid and thiamethoxam, while only Wolbachia was found in case of acetamiprid. Expression analysis demonstrated differential upregulation of insecticide resistance genes with Purulia and Hooghly populations showing maximally upregulated P450 genes. Moreover, thiamethoxam and imidacloprid resistance ratio (RR) showed a significant correlation with CYP6CM1, CYP6DZ7, and CYP4C64 genes, while acetamiprid RR correlated with CYP6CX1, CYP6DW2, CYP6DZ7, and CYP4C64 genes. Taken together, these findings suggested that P450 mono-oxygenase and symbiotic bacteria together affected whitefly resistance to neonicotinoids. Hence, a symbiont-oriented management programme could be a better alternative to control or delay resistance development in whitefly and can be used for pesticide clean-up in an agricultural field.
Background The invasive and calamitous polyphagous pest Spodoptera frugiperda or commonly known as fall armyworm (FAW) poses serious menace to the global agricultural production. Owing to the revamped invasion of FAW in 2018 in India, present study was undertaken for precise assessment of its genetic identity and pesticide resistance to aid in pest-management strategies. Results To evaluate the diversity in FAW population across Eastern India, mitochondrial COI sequences were used which revealed a low nucleotide diversity. Analysis of molecular variance indicated significant genetic variation between four global geographical FAW populations with lowest differentiation between India and Africa suggesting a present-day and shared origin of FAW. The study demonstrated existence of two different strains (‘R’ strain and ‘C’ strain) based on COI gene marker. However, discrepancies between COI marker and host plant association of FAW was observed. Characterization of Tpi gene revealed abundance of TpiCa1a followed by TpiCa2b and TpiR1a strains respectively. The FAW population showed higher susceptibility towards chlorantraniliprole and spinetoram than cypermethrin. Insecticide resistance genes depicted marked upregulation although with lot of variance. Chlorantraniliprole resistance ratio (RR) exhibited significant correlation with 1950 (Glutathione S-transferase, GST), 9131 (Cytochrome P450, CYP) and 9360 (CYP) genes, while spinetoram and cypermethrin RR was found to correlate with 1950 (GST) and 9360 (CYP) genes. Conclusion This study manifests Indian subcontinent as the potential new hotspot for the growth and distribution of FAW population that can be effectively controlled using chlorantraniliprole and spinetoram. This study also adds novel significant information on FAW population across Eastern India for developing a comprehensive pest management approach for S. frugiperda.
Gap junctions are integral membrane proteins that play a role in cell-to-cell communication. They are coded by the functional genes called connexins in chordates and innexins in invertebrates. However, recently pannexins were also found in mammalian genomes, which are homologous to insect innexins. Gap junction intercellular communication (GJIC) has different functions ranging from their role in ontogenesis to the transfer of intracellular signal molecules and minimizing the adverse effects of xenobiotics by dilution and steady-state catabolism. Perturbations of these gap junctions are known to promote cancers besides, and many tumor inducers reduce the functioning of these gap junctions. Insect gap junctions play a crucial role in the development of insects and perhaps might be one of the reasons for the success of insects on terrestrial habitats. Majority of the work on innexins was done on Drosophila melanogaster Meigen, 1830 (Diptera: Drosophilidae), and its innexins regulate size of the central nervous system, embryonic gut formation, metamorphosis, and the fertility of germ lines in the reproductive system. There are several insecticides like cyclodienes, organochlorines, phenypyrazoles, synthetic pyrethroids, avermectins, milbemycins, oxadiazines, semicarbazones, meta-diamides, isoxazolines which target ion channels in the insects, but there is no evidence that supports the possible toxic effects of insecticides on insect gap junctions. In this review, we discuss the importance of insect gap junctions and how they could be a potential target for chemical pest management.
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