Acute and sublethal toxicity of novaluron, a novel chitin synthesis inhibitor, to Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

The acute and sublethal toxicities of novaluron, a novel chitin synthesis inhibitor, to a laboratory‐reared insecticide‐susceptible strain of Colorado potato beetle, Leptinotarsa decemlineata (Say), were determined. Novaluron exhibited excellent residual (120 h LC50 = 0.42 mg litre−1) and good direct contact (120 h LC50 = 27 mg litre−1) activity against second‐instar larvae (L2). Hatch of eggs exposed by direct contact to novaluron solutions ≥100 mg litre−1 was significantly reduced, as was the ability of emerged first‐instar larvae to moult. L2 from eggs exposed to ≥100 mg litre−1 novaluron weighed significantly less (P < 0.0001) than those from untreated eggs. However, L2 from eggs treated with 1 mg litre−1 novaluron weighed significantly more (P ≤ 0.05) than those from untreated eggs, suggesting novaluron can have a hormetic effect on L decemlineata larval development. Leptinotarsa decemlineata mating pairs fed foliage treated with novaluron at 25 or 75 g AI ha−1 produced approximately 25% fewer egg masses and eggs per mass. Hatch of eggs on treated foliage was almost completely suppressed, and longevity of male beetles was reduced by approximately 50% when fed foliage treated with novaluron at 75 g AI ha−1.