Evaluation and optimization of blends for attracting Trichogramma dendrolimi based on semiochemicals mediating tritrophic interactions in the orchard habitat

Trichogramma dendrolimi Matsumura (Hymenoptera: Trichogrammatidae) is one of the most important parasitic natural enemies of Grapholita molesta (Busck) (Lepidoptera: Tortricidae) in peach and pear orchards. The artificial rearing T. dendrolimi have been widely used in biological control programs in recent years. However, its actual parasitic effect on the pest in the field is less, so it is important to develop attractants to increase the parasitic efficiency of the parasitoids. T . dendrolimi can be easily attracted by semiochemicals derived from flowers, intact plants, herbivore-attacked plants, and insects in its orchard habitats. In this paper, 73 semiochemicals were evaluated as potential attractants at three concentrations (0.1 mg/mL, 1 mg/mL, and 10 mg/mL) to T . dendrolimi by Y-tube olfactometer bioassays and Electroantennogram (EAG) technology, and then the mixtures of active individual compounds were further tested and evaluated in the field. As a result, 17 individual compounds showed attractive bioactivity to T . dendrolimi . Interestingly, when methyl salicylate and benzaldehyde mixed with linalool oxide or cis -3-hexenyl caproate in a volume ratio of 10:3:3 respectively showed excellent attractant bioactivity for T . dendrolimi in the orchard field. Thus, introducing such parasitoid attractants in orchard habitat may improve the biological control effect to pests.