Lethal and sublethal effects of imidacloprid and pirimicarb on the melon aphid, Aphis gossypii Glover (Hemiptera: Aphididae) under laboratory conditions

The toxicity of imidacloprid and pirimicarb for all stages of the melon aphid, Aphis gossypii Glover, were investigated under laboratory conditions (۲۵ ± ۱ oC, ۶۵ ± ۵% R.H. and a photoperiod of ۱۶:۸ (L: D) h.) using a leaf dipping method. These pesticides were very toxic for first instar nymphs of A. gossypii with LC۵۰ values of ۱۷ and ۲۲۰.۲ ppm for imidacloprid and pirimicarb, respectively. For other nymphal instars, values of ۲۳.۹ to ۷۰.۵ ppm and ۳۰۸.۸ to ۷۸۱.۷ ppm were recorded for imidacloprid and pirimicarb respectively. Their LC۵۰ values for adults were ۹۰.۱ and ۹۸۳.۱ ppm, respectively. Toxicity decreased with increasing age. Imidacloprid was more toxic than pirimicarb for all stages of development. The effect of applying sublethal concentrations of imidacloprid and pirimicarb was evaluated, also, using demographic toxicology. Longevity and population growth parameters, including intrinsic rate of increase (rm), net reproductive rate (R۰), generation time (Tc) and finite rate of population increase (λ), were affected negatively by both insecticides. The rm values for control, imidacloprid and pirimicarb exposed populations were ۰.۴۳۸, ۰.۱۵۰ and ۰.۳۳۵ female offspring per female per day, respectively. The doubling time (DT) also, was affected by imidacloprid. Overall, these results suggest that imidacloprid and pirimicarb can be effective against A. gossypii.

Keywords:

Aphis gossypii , Carbamate , Demographic toxicology , Neonicotinoid