Laboratory evaluation of two novel strategies to control first‐instar gypsy moth larvae with spinosad applied to tree trunks

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Abstract
Two strategies for controlling first‐instar larvae of gypsy moth (Lymantria dispar (L)), insecticidal bait and contact insecticide applied directly to the tree trunk, were evaluated in the laboratory. Spinosad was selected as a candidate natural‐product insecticide that is active both by contact and ingestion. Incorporated into artificial diet‐based bait, spinosad was toxic to neonate larvae with a minimal 10‐s feeding period, with an LC50 value of 20 (15–26, 95% confidence interval) mg liter−1. It was significant that neonate larvae did not discriminate between spinosad‐treated and control diet. Efficacy of diet‐based bait in the laboratory, however, was significantly impacted by previous exposure to diet; fed larvae did not stop at the bait and did not incur mortality, as compared to unfed larvae. Oak bark was a suitable substrate from which neonate larvae could contact spinosad residues. Spinosad applied directly to oak bark resulted in significant mortality after 1‐ and 4‐min crawling contact exposure times (LC50 = 24 [20–29, 95% CI] and 8.7 [6.9–11, 95% CI] mg liter−1, respectively) and contact activity persisted for 2 weeks. While contact activity was more potent on glass surfaces than on oak bark, the LC50 values differed only by factors of 2.4 and 3.6, for 1‐ and 4‐min exposures respectively.© 2002 Society of Chemical Industry

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