Effects of spirotetramat insecticide on life history traits and population growth of Encarsia formosa (Hymenoptera: Aphelinidae)

Abstract

ABSTRACT Sublethal effects of a spirotetramat insecticide on life history traits and population growth of two local Serbian populations (Bujanovac and Negotin) and one commercial Dutch population (the Dutch strain) of Encarsia formosa Gahan (Hymen.: Aphelinidae) were evaluated in laboratory bioassays. Median lethal concentrations of spirotetramat estimated in the acute toxicity bioassay with adults (250 mg/l for Bujanovac and Negotin populations, and 225 mg/l for the Dutch population), significantly reduced the longevity of adult wasps exposed for 48 h to fresh residues by 1.6–2.8 days. Total parasitism of exposed adults, adult emergence in the F1 generation, and the instantaneous rate of increase of surviving wasp populations were significantly reduced (<30%). When applied to pupae within parasitised hosts (at LC50s estimated in the acute toxicity bioassay with pupae; 700 mg/l for Bujanovac and 600 mg/l for the Negotin and Dutch populations), the spirotetramat significantly extended the development of juveniles (by 1–1.4 days), and significantly reduced longevity (by 0.7 days) and the instantaneous rate of increase for the Bujanovac wasps, by 6.1%. According to the estimated acute toxity for both adults and pupae of E. formosa and taking into account the reduction of reproductive and demographic parameters (<30% in bioassays with adults and <10% in bioassays with pupae), spirotetramat can be classified as compatible with E. formasa in integrated whitefly management.