An integrated management strategy for Grapholita molesta (Lepidoptera: Tortricidae) combining chemical, physical, and biological control tactics

Abstract

We evaluated the acute and residual toxicity of emamectin benzoate (EB) and mineral oil to the oriental fruit borer, Grapholita molesta, and its egg parasitoid, Trichogramma dendrolimi. EB exhibited high toxicity to G. molesta larvae (LC₅₀ = 6.33 mg L⁻¹) and adults (LC₅₀ = 5.50 mg L⁻¹) but low ovicidal activity (25.3 % mortality at 18.82 mg L⁻¹). Topical application of EB caused 100 % mortality of T. dendrolimi adults, and the parasitism success of females surviving 7 d-old residues was reduced by 73.3 %. Sublethal exposure to EB (2.35 mg L⁻¹, LC₂₅) prolonged the preoviposition period of G. molesta by 1.3 days and reduced fecundity by 42 %. Mineral oil at 6.67 mL L⁻¹ caused 95.4 % and 65.7 % mortality of G. molesta eggs and larvae, respectively, but also harmed T. dendrolimi (LC₅₀ = 4.50–5.55 mL L⁻¹), reducing parasitism and emergence by > 30 %. An integrated management strategy was developed based on these data, and considering seasonal fluctuations in the commercial availability of T. dendrolimi. We conclude that EB should target overwintered mature larvae and newly emerged G. molesta adults in early spring, when T. dendrolimi are in short supply, and be followed by a mineral oil application for egg control. EB should be applied to peak moth flights from late spring to early autumn, with releases of T. dendrolimi following ca. one week later. This strategy would capitalize on the stage-specific vulnerability of the pest to specific control tactics and use careful timing of releases to protect parasitoids, while simultaneously mitigating the evolution of resistance to EB in the pest.