Residual activity of insecticides applied against Lobesia botrana and its influence on resistance management strategies.

Some insect growth disruptors, in particular chitin synthesis inhibitors (benzoylphenyl ureas) and ecdysone agonists (bisacylhydrazines), show high efficacy against Lobesia botrana (Denis et Schiffermuller) (Lepidoptera Tortricidae) and are characterized by a longer residual activity than the traditional organophosphate active ingredients. Previous research had shown that the persistence of some active ingredients applied against the first generation of L. botrana also ensured control of the second generation. In this study, the residual activity of insecticides applied against the second generation was evaluated on the third generation in field trials and laboratory bioassays. Methoxyfenozide controlled the third generation at the same efficacy level (more than 90%) when applied against the second or the third generations. Some residual activity was observed in the field also for indoxacarb (efficacy 75%). In contrast, a very low residual activity (efficacy lower than 30%) was recorded for chlorpyrifos. Because a longer residual activity is associated with a higher risk of selecting insecticide resistant populations, operational resistance management strategies are discussed to ensure a longer usable life span of these insecticides.