Testing of selected insecticides to assess the viability of the integrated pest management of the Eucalyptus snout‐beetle Gonipterus scutellatus in north‐west Spain

Abstract

Abstract: We investigated, by means of topical, residual and field assays, the toxicity of four insecticides (Bacillus thuringiensis, azadirachtin, flufenoxuron and ethofenprox) to adult, larvae and eggs of the Eucalyptus snout‐beetle Gonipterus scutellatus and their side‐effects on the adults of the solitary egg parasitoid Anaphes nitens, its natural enemy. In the topical toxicity experiment, both flufenoxuron and ethofenprox severely affected G. scutellatus, causing 100% adult mortality after 7 days, and 75 and 100% larval mortality, respectively. Ethofenprox also caused 93% larval pre‐eclosion mortality and 100% parasitoid mortality. In the residual experiment, azadirachtin acted as an effective larvicide when ingested (73% mortality after 7 days). Ethofenprox showed the highest toxicity, with 100% mortality of adults and larvae of G. scutellatus after 24 h. On the day 7 of observation, flufenoxuron resulted in 93% adult mortality and 100% larval mortality. After contact with residuals, only ethofenprox and flufenoxuron had adversely affected A. nitens (98% mortality after 48 h). Bacillus thuringiensis exhibited only a slight activity against the pest or the parasitoid. The field experiment was carried out on three localities, with a preliminary sampling, and three samplings after the applications of the products, on days 7, 14 and 30. We evaluated the parasitism rate, parasitoid sex ratio, parasitoid pre‐eclosion mortality, the abundance of G. scutellatus adults, larvae and egg capsules, the pre‐eclosion mortality rate of weevil eggs and larvae and the foliar damage. Only fluenoxuron and ethofenprox reduced the pest population and the foliar damages, but ethofenprox also significantly decreased the rate of parasitism (17%) after 7 days. Given our experimental results, we suggest that flufenoxuron and azadirachtin could be used in association with the natural enemy.