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

Abstract

BACKGROUND 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. RESULTS 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. CONCLUSION We calculated that, for each generation of G. molesta, 900 000 wasps per hectare, in three releases 3 days apart, each distributed among release points 10 m 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

Laboratory evaluation of the compatibility of Beauveria bassiana with the egg parasitoid Trichogramma dendrolimi (Hymenoptera: Trichogrammatidae) for joint application against the oriental fruit moth Grapholita molesta (Lepidoptera: Tortricidae)

“…Containers with eggs were cut into pieces and the resulting egg cards were placed next to apples so that eclosing neonates could bore into the apples, where they completed larval development. 16,39 T. dendrolimi were purchased from Gongzhuling Jinong Green Agriculture High-tech Development Co., Ltd (Jilin, China), where they were reared in eggs of Antheraea pernyi (Guerin-Meneville) (Lepidoptera: Saturniidae). The laboratory colony of T. dendrolimi used for experiments was maintained on eggs of the rice moth, Corcyra cephalonica Stainton (Lepidoptera: Pyralidae), for more than 30 generations.…”

“…An assessment of the potential for intraguild effects and possible antagonistic interactions between B. bassiana and T. dendrolimi is therefore a prerequisite for their joint application in a management program for G. molesta. 16,32,37,38 The present study had three objectives: (i) to assay the pathogenicity of B. bassiana to both G. molesta and its parasitoid, T. dendrolimi; (ii) to assay any potential effects of B. bassiana infection on host egg acceptability and suitability for parasitism by T. dendrolimi; and (iii) to explore the potential of T. dendrolimi as a vector of B. bassiana when emerging from infected eggs. The results were expected to provide information useful for ensuring the compatibility of simultaneous applications of these two biocontrol agents against G. molesta in fruit orchards.…”

“…Females of Trichogramma dendrolimi Matsumura (Hymenoptera: Trichogrammatidae) are proovigenic, time‐limited parasitoids 14 . In China, releases of T. dendrolimi in fruit orchards are often carefully timed to target G. molesta eggs before they can hatch 15,16 . To enhance biocontrol efficacy, the combined application of multiple biological control agents is often recommended, 17 but the sensitivity of tiny egg parasitoids to various biotic and abiotic mortality factors may limit their compatibility with other control agents.…”

“…For example, B. bassiana can be lethal to adults of the parasitoid Aphidius colemani Viereck (Hymenoptera: Braconidae) under greenhouse conditions 31 and has adverse effects on the oviposition behavior of the parasitoid Trybliographa rapae (Westwood) (Hymenoptera: Figitidae) under laboratory conditions 32 . In fruit orchards, three releases of T. dendrolimi 3 days apart are recommended for control of each G. molesta generation, 16 and the adult parasitoids face exposure to B. bassiana when the fungus is applied simultaneously to enhance control of adult moths and neonate larvae. There also exists the possibility that conidia adhering to G. molesta eggs might reduce their susceptibility to parasitism by the wasp or reduce the fitness of surviving wasp offspring.…”

“…For these reasons, the potential compatibility of EPFs with egg parasitoids in augmention programs have often been evaluated 33‐36 with a view to optimizing application techniques to avoid any potential adverse effects of the EPF on the parasitoids. An assessment of the potential for intraguild effects and possible antagonistic interactions between B. bassiana and T. dendrolimi is therefore a prerequisite for their joint application in a management program for G. molesta 16,32,37,38 . The present study had three objectives: (i) to assay the pathogenicity of B. bassiana to both G. molesta and its parasitoid, T. dendrolimi ; (ii) to assay any potential effects of B. bassiana infection on host egg acceptability and suitability for parasitism by T. dendrolimi ; and (iii) to explore the potential of T. dendrolimi as a vector of B. bassiana when emerging from infected eggs.…”