Biochemical mechanisms of flonicamid resistance and its transgenerational effects in Bemisia tabaci mitotype...

Bemisia tabaci is amongst noxious pest of the cotton, vegetables and ornamentals. Insecticides, for instance neonicotinoids, carbamates, organophosphates and pyrethroids are employed to control B. tabaci. Owing to the excessive use of chemicals, high level of resistance has been developed in B. tabaci. Flonicamid, a systemic insecticide inhibits insect's feeding and is potent against B. tabaci. The potential mechanisms underlying resistance to flonicamid in B. tabaci Asia-II-1 were investigated for 16 generations and biochemical assays were performed for the possible involvement of enzymes in the resistance development. In addition, the transgenerational effects were also assessed. Flonicamid resistant strain was developed with 161.5 folds increase in resistance at 16th generation (LC₅₀ = 1376.8 mg/L) compared to the susceptible UNSEL population (LC₅₀ = 8.52 mg/L). The biochemical analysis revealed substantial rise in the activities of glutathione S-transferases and esterases after exposure to flonicamid, while acetylcholinesterase, alkaline and acid phosphatase showed slight increase in activity. The increased activity may possibly favor flonicamid resistance. In the parental generation (F₀), treatment with flonicamid at low (LC₃₀) and high (LC₅₀) concentrations reduced fecundity to 60.85 and 43.88 eggs per female, compared to 77.55 in the control. Female longevity decreased to 26.42 (LC₃₀) and 23.12 (LC₅₀) days, compared to 29.45 days in the control, while male longevity dropped to 25.81 (LC₃₀) and 21.84 (LC₅₀) days, compared to 27.47 days in F₀. In the F₁ generation, total longevity decreased to 23.73 (LC₃₀) and 19.87 (LC₅₀) days, compared to 27.02 days in the control. Female longevity was reduced to 26.35 (LC₃₀) and 23.04 (LC₅₀) days, compared to 29.32 days in the control, and male longevity was decreased to 25.69 (LC₃₀) and 21.72 (LC₅₀) days, compared to 27.38 days in the control. The mean generation time (T), intrinsic rate of increase (r), and net reproductive rate (R₀) were significantly reduced in both LC₃₀ and LC₅₀ treatments compared to the control, with more pronounced effects observed at LC₅₀. The current study imparts a thorough analysis of the insecticide resistance development and changes in enzyme activities. Our findings provide detailed information about the general impact of flonicamid on B. tabaci, which might be helpful for its management.