Laboratory selection for insecticide resistance in the leafminer natural enemy, Ganaspidium utilis Beardsley (Hymenoptera: Eucoilidae)

Ganaspidium utilis Beardsley (Hymenoptera: Eucoilidae), a parasitoid of Liriomyza leafminers, was laboratory-selected for fenvalerate resistance. After 22 generations of fenvalerate selection using G. utilis adults over a total of 50 generations, the Exposure of G. utilis adults to foliage treated with various rates of fenvalerate (0.056, 0.112, 0.224 and 0.448 kg AI fenvalerate/ha) using a boom sprayer and different post exposure times (2, 24, 48 & 72 hours) indicated significantly higher mortality in the Baseline strain compared to the Select strain in most treatments. When exposed to bean foliage 2 hours after fenvalerate treatment at the recommended field rate (0.224 kg AI/ha), the Select strain exhibited significantly higher survivorship (72 percent) compared with the Baseline strain (27 percent).Assessment of parasitoid susceptibility to esfenvalerate, malathion, oxamyl and methomyl using plastic cups showed significantly higher Following 24 hr exposure to 3,000 ppm fenvalerate, the Select strain exhibited normal progeny production and sex ratios (1.00:1.42 M:F) compared with the Baseline strain in which progeny production was 37 percent less and the sex ratio was highly male biased (1.00:0.58 M:F). No reduction in fitness was found in the Select strain. Genetic analysis using the back cross method suggested an additive, polygenic mode of inheritance of fenvalerate resistance in the Select strain.If established in the field, the Select strain may be useful in reducing pest resurgences and secondary pest upsets associated with Liriomyza leafminers in sprayed habitats.