Enhancing parasitism of the introduced ash tree pest, Caloptilia fraxinella by native parasitoid, Apanteles polychrosidis in Edmonton, Alberta: Not just a matter of more parasitoids being attracted to infested trees

Abstract: Hymenopteran parasitoids are widely studied and employed as biological controls to reduce populations of pest insects. Apanteles polychrosidis Vierek (Hymenoptera: Braconidae) is a native parasitoid wasp that has shifted hosts, becoming the primary parasitoid of the ash leaf-cone roller, Caloptilia fraxinella Ely (Lepidoptera: Gracillariidae), an introduced nuisance pest of ash trees (Fraxinus spp.) in Edmonton, Alberta. This project explores two approaches to enhance A. polychrosidis as a biological control agent of C. fraxinella: 1) Baiting trees with synthetic semiochemical lures that release methyl salicylate (MS), and two green leaf volatiles (GLVs) (Z)-3 hexenyl acetate, and (Z)-3-hHexanol to enhance wasp attraction and parasitism in infested ash trees. Mated female wasp attraction to these same compounds was tested also tested in an olfactometer. Male and female wasps were more attracted to ash trees treated with the combination of MS+GLV lures, at the lower release rate tested. Mated females did not demonstrate attraction to VOC compounds in the olfactometer. 2) Nutritional provisioning with 10% and 25% sucrose solution or natural nectar sources to enhance retention of wasps in ash trees and increase parasitism of C. fraxinella. The effect of sucrose nutrition on wasp longevity, female fecundity and parasitism, and offspring fitness were measured in the laboratory. Wasp longevity was greater in virgin male and female A. polychrosidis that were fed either 10 or 25% sucrose solution. Females lived significantly longer than males, when they were both fed 25% sucrose. Virgin female egg load was lower for wasps fed 25% sucrose, and female egg load was negatively correlated with female longevity. Nectar feeding extended virgin female longevity similarly to those fed 25% sucrose. Neither sucrose solution, nor buckwheat flower provision in the field increased wasp retention. Wasp density was negatively correlated with C. fraxinella host density in field experiments.