Sublethal effect of imidacloprid and pymetrozine on the numerical response of the parasitoid wasp, Lysiphlebus fabarum (Hym.: Braconidae)

The application of pesticides may affect biological characteristics, behavior and efficiency of natural enemies. In this research, sublethal effect of two insecticides imidacloprid and pymetrozine was investigated on the numerical response of Lysiphlebus fabarum (Marshall) under laboratory conditions. The parasitoid wasps (< 12 h old) exposed to residual concentrations of 3.2 and 2586.6 ppm (LC25) of imidacloprid and pymetrozne, respectively in glass vials. After 24 h, six pairs randomly alived parasitoid wasps were selected and each pair were transferred to containers containing seedlings infested by different densities (2, 4, 8, 16, 32, and 64) of the third instar of Aphis fabae Scopoli nymphs. Each density had 15 replications. Mortality and fecundity of the L. fabarum were recorded every 24 h. until the females died. Mean longevity and number of produced mummies during life of parasitoid wasps exposed to LC25 of imidacloprid were significantly lower than control and pymetrozine treatment at most densities of host aphid. According obtained results, imidacloprid had more negative effects than pymetrozine on L. fabarum adults. Therefore, the application of pymetrozine is recommended for integrated control of A. fabae.