Abstract

The compatibility of chemical control with biological control is important but not simple because most insecticides can adversely affect biological control agents, such as the parasitoid Goniozus legneri (Gordh) (Hymenoptera: Bethylidae). The aim of this study was to assess the lethal and sublethal effects on parasitism and adult emergence) of commercial insecticides under laboratory conditions. It utilized spirotetramat (mixed with thiacloprid), bifenthrin, pirimicarb, and imidacloprid on the adults of G. legneri at field doses and 1/2, 1/4, 1/8, and 1/16 of this concentration by either direct spraying or exposure to treated surfaces. Spirotetramat mixed with thiacloprid caused the lowest mortality (spraying 12.2%, residual 13.3%). In direct spraying, this mixture of insecticides caused the lowest reduction of both parasitism -2 .2% and the emergence of F1 adults -23.2% at its highest doses compared to the control. Bifenthrin caused 100% mortality at its highest concentrations 4.0 and 8.0 g hl-1) when applied directly. The mortality of G. legneri adults following treatment with pirimicarb was higher in surface exposure (67.6%) than in direct sprays (24.7%). Imidacloprid caused a complete reduction in parasitism and the development of G. legneri progeny -100% when sprayed directly. No insecticide treatment affected or promoted the parasitoid's preference for the treated larvae. Under field conditions, the G. legneri adults have the option to move away from treated areas. However, if they come into contact with a commercial spray, the lethal and sublethal effects of spirotetramat plus thiacloprid are lower compared to exposure to the other insecticides evaluated. Spirotetramat mixed with thiacloprid was the least toxic insecticide for the G. legneri adults, while bifenthrin and imidacloprid were the most toxic.