Sublethal effects of a Beauveria bassiana-based mycopesticide on Dutch and Serbian populations of Encarsia formosa (Hymenoptera: Aphelinidae)

Abstract

ABSTRACTThe effects of a Beauveria bassiana-based product (trade name Naturalis-L; strain ATCC 74040) on the behaviour, life history traits and population growth of one commercial Dutch strain and two local Serbian populations (Bujanovac and Negotin) of Encarsia formosa Gahan (Hymen.: Aphelinidae) were evaluated in laboratory bioassays. In a two-choice test, parasitoids from all tested populations preferred to parasitise untreated whitefly nymphs over those treated with 1, 0.5, 0.25, 0.125 and 0.0625 ml/l of the mycopesticide. The longevity of adults of population Bujanovac exposed for 48 h to residues of the mycoinsecticide applied at the LC50 concentration was 1.4 days shorter than that of control wasps. Total parasitism was significantly reduced (by 17.5, 26.2 and 31.4% for the Negotin, Dutch and Bujanovac populations, respectively) compared to control, as well as adult emergence in the F1 generation (reductions of 20.3 and 26.7%, for the Dutch and Bujanovac populations, respectively). The instantaneous rate of increase (ri) of surviving adults was also significantly reduced by mycopesticide treatment by 6.3, 13.8 and 15.1%, for the Negotin, Bujanovac, and Dutch populations, respectively. Adult parasioids emerged from pupae treated with the LC50 concentration of the mycopesticide showed slower juvenile development, longevity, parasitism, adult emergence, and ri values, but the reduction in ri was significant only for the Bujanovac and Dutch populations (4.2 and 8.3%, respectively). The implications of these results on integrated control of the greenhouse whitefly Trialeurodes vaporariorum Westwood (Hem.: Aleyrodidae) are discussed in terms of adjusting the timing of Naturalis-L applications and parasitoid release.