Acute toxity and sublethal effects of pymetrozine on the whitefly parasitoid Encarsia formosa Gahan

摘要

Sublethal eff ects of a pymetrozine-based product (commercial product Chess 50 WP)on life history traits and population growth of one commercialized strain (“Dutch” strain)and two local populations (Bujanovac and Negotin) of the whitefl y parasitoid Encarsiaformosa Gahan (Hymenoptera: Aphelinidae) were evaluated in laboratory bioassays. Alltrials were carried out at 27±1°C temperature and under 60±10 % relative humidity and16/8 h daylight/darkness photoperiod in four replications. Longevity of wasps exposed for48 h to residues of the pymetrozine insecticide (LC50, 280 mg a.i./l) was shorter (by 2.7-3 days)than that of control wasps. Total parasitism of Negotin wasps was signifi cantly reduced (by8.2 %), as well as total parasitism and adult emergence of the Dutch strain (by 7.3 and 8.2 %,respectively), compared to control wasps. The instantaneous rate of increase (ri) of survivingadult wasps was also signifi cantly reduced (by 6.6, 6.3 and 7.6 % in populations Negotin,Bujanovac and Dutch strain, respectively). Direct treatment of wasps at their pupal stage(LC50, 300 mg a.i./l) reduced total parasitism of Negotin wasps (by 8 %), and reduced rilevels,but the reduction was signifi cant only for the Bujanovac (by 6.7 %) and Negotin (by 4.6%) populations. Juvenile development of the parasitoid in treated pupae was signifi cantlyextended (by 0.3-1.1 days), compared to control wasps. The implications of these results onintegrated control of the greenhouse whitefl y are discussed.