Laboratory and field studies supporting augmentation biological control of oriental fruit moth, Grapholita molesta (Lepidoptera: Tortricidae), using Trichogramma dendrolimi (Hymenoptera: Trichogrammatidae).

Abstract

Oriental fruit moth, Grapholita molesta (Busck) (Lepidoptera: Tortricidae) is a cosmopolitan pests of fruit trees in temperate regions. Control of G. molesta is challenging because larvae feed in concealed locations and have evolved resistance to many pesticides. We compared three commercially available species of Trichogramma for efficacy against G. molesta in the laboratory assays and tested releases of the promising species in a pear orchard. Laboratory assays indicated that Trichogramma dendrolimi parasitized G. molesta at the highest rate. Parasitoids took longer to oviposit in older host eggs, and fewer eggs were parasitized when they were more than 3 days old. Field tests produced ca 60% cumulative parasitism of sentinel G. molesta eggs with one release of Trichogramma dendrolimi, with most parasitism occurring within 24 h. Female wasps dispersed up to 12 m from release points with a bias toward upwind movement. We calculated that, for each generation of G. molesta, 900000 wasps per hectare, in three releases 3 days apart, each distributed among release points 10m apart, would reduce fruit damage by half in an orchard where 50% of fruit would otherwise be damaged. Although augmentation of Trichogramma dendrolimi is a viable tactic for reducing G. molesta populations and fruit damage, it will require integration with other compatible control tactics in order to provide commercially acceptable levels of control in orchards experiencing significant pest pressure. © 2021 Society of Chemical Industry.