Lethal and Sublethal Effects of Avermectin B1 on the Western Spruce Budworm (Lepidoptera: Tortricidae)

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Abstract
Laboratory studies were conducted to estimate the minimum application rate of Avermectin B1 necessary for 90% reduction of Choristoneura occidentalis Freeman larva populations in the field, the most advantageous time during larva population development for application, the chemical’s effects when applied to eggs, and latent effects on the progeny of insects surviving treatment in the last instar. The earliest time to achieve 85–95% mortality was ca. 30 days after emergence of the first group of second instars from diapause. Field-application rates were estimated to be 3.5, 7.1, and 10.6 g/ha (if Avermectin B1 is rainfast) or 4.4, 8.8, and 13.3 g/ha (if it is not rainfast). Concentrations of 0.071 and 0.71 g/ha significantly inhibited subsequent development of larvae treated as eggs, while the effects of lower concentrations were not significant. The fecundity of mated adult survivors sprayed with Avermectin B1 at LC50 as sixth instars was not affected, but the fertility of their eggs was significantly reduced. Sterility, rather than inhibition of hatching, appeared to account for the fertility effect. These results suggest that Avermectin B1 might be an alternative to conventional chemicals used for C. occidentalis management.