Sublethal effects of three insecticides on life table parameters of the parasitoid wasp, Lysiphlebus fabarum

 Demographic toxicology is usually the best way to evaluate total effects of pesticides on a population of natural enemy. Lethal and sublethal effects of imidacloprid, pymetrozine and Dayabon® were investigated on the sexual population of Lysiphlebus fabarum at laboratory conditions. Toxicity of the insecticides on immature stages of L. fabarum was evaluated, by dipping leaves containing parasitized Aphis fabae. These insecticides significantly reduced adult emergence rate when parasitized aphids were treated with field-recommended concentrations at larval stage. Imidacloprid had more toxicity than pymetrozine and Dayabon® at pupal stage. Imidacloprid was significantly more toxic than pymetrozine at adult stage. Dayabon® did not have residual effect on adults. In order to assess sublethal effects of three insecticides on life-table parameters of L. fabarum, the concentrations that had 25% mortality threshold and field-recommended concentrations were used for larval, adult and pupal stages treatments, respectively. Adults’ longevity, mean fecundity, females' oviposition period, sex ratio and some population parameters (r,λ, R0) were negatively affected by application of imidacloprid in comparison with other insecticides and control at larval, pupal and adult stages treatments. The intrinsic rate of increase (r) values for imidacloprid treatment and control at larval, pupal and adult stages of parasitoid were 0.2035 ± 0.01, 0.2240 ± 0.01 and 0.2273 ± 0.01 (day-1) and 0.2635 ± 0.01, 0.2759 ± 0.01 and 0.2687 ± 0.01 (day-1), respectively. According to obtained results, pymetrozine and Dayabon® could be used to control A. fabae in combination with L. fabarum.