Sublethal effects of NeemAzal- T/S botanical insecticide on Dutch and Serbian populations of Encarsia formosa (Hymenoptera: Aphelinidae)

Abstract

ABSTRACTSublethal effects of an azadirachtin-based botanical insecticide (commercial product NeemAzal-T/S) on behaviour, life history traits and population growth of one commercial (Dutch strain, D) and two Serbian populations (Bujanovac, B; Negotin, N) of Encarsia formosa Gahan were evaluated in laboratory bioassays. In a two-choice test, parasitoids from all tested populations preferred to parasitise the untreated whitefly nymphs over those treated with 50, 25, 12.5, 6.25 and 3.12 mg/l of azadirachtin. All concentrations caused significant deterrent effects after 24 h, and the following deterrence indices were calculated: 9.7–60.9% (B), 5.5–57.5% (N) and 12.9–63.5% (D). The longevity of adults exposed for 48 h to residues of the botanical insecticide (applied at LC50) was shorter (1.5–1.7 days) than that of control wasps. Both daily and total parasitism were significantly reduced (by 41.7, 48.3 and 60.1% for N, D and B, respectively) compared to control, as well as adult emergence in the F1 generation. The instantaneous rate of increase (ri) of surviving adults was also significantly reduced (by 13.2, 19. 3 and 20.5%, for populations N, B, and D, respectively). Adults from all tested populations, emerged from pupae treated with the botanical insecticide applied at LC50, showed reduced parasitism, adult emergence, and ri levels, but the reduction was significant only for adult emergence of B and ri of B and N. Juvenile development of the parasitoid in treated pupae was significantly extended, compared to control. The implications of these results on integrated control of the greenhouse whitefly are discussed.