Relationship between susceptibility to neonicotinoids and population dynamics of cotton aphid,Aphis gossypii Glover (Hemiptera: Aphididae)

Efficiency of imidacloprid and thiametoxam on population growth parameters of Aphis gossypii Glover (Hemiptera: Aphididae) was assessed using three bioassay methods including; residual, starvation and FAO dip methods. Aphids were assayed under laboratory conditions at 23 ± 2°C, photoperiod of 16:8 (L:D) and 70% relative humidity. Aphids were transferred to sprayed leaves and Petri dishes in residual and starvation methods, respectively. There was no feeding for the aphids in starvation method. In FAO dip method, insects were dipped for 5 s in pesticide solutions and then transferred to fresh leaves. Results revealed that LC₅₀ values calculated with the starvation and residual methods were respectively 15 and 11% more than FAO dip method (for imidacloprid) and 22 and 18% (for thiametoxam). The LC₅₀ value in starvation method was 3% more than the residual method. Calculated LC₅₀ in starvation and residual methods with imidacloprid respectively caused 160 and 34% increase in intrinsic rates of increase (r _m) and net reproductive rate (R ₀) in comparison with FAO dip method. Generation time (T) and doubling time (DT) were respectively 59 and 62% less than those in FAO dip method. In contrast, thiametoxam (LC₅₀ concentration) in starvation and residual method lead to 9 and 67% increase in r _m and R ₀ parameters compared to FAO dip method. However T and DT were respectively 65 and 92% less than mentioned parameters in FAO dip method. There was not any significant difference between life table parameters calculated by residual and starvation bioassay methods.