Search

Abstract: The ash leaf-coneroller, Caloptilia fraxinella (Ely) (Lepidoptera: Gracillariidae) is an introduced moth to the urban forest of Western Canada that specializes on ash (Fraxinus spp.) (Oleaceae). It uses green ash, F. pensylvannica Marsh. var. subintegerrima (Vahl) Fern, and black ash, F. nigra Marsh in its expanded range but prefers black over green ash for oviposition. The oviposition preference for black ash was not linked to enhanced performance of offspring on black ash as green ash supported higher larval survival and faster development than black ash. Younger leaflets are preferred by female moths over older leaflets and green ash elicits more host location flight by gravid females than black ash in wind tunnel experiments. Caloptilia fraxinella adults are attracted to volatile organic compounds (VOCs) released from ash seedlings. The antennae of mated female C. fraxinella consistently detect six VOCs released from black ash and green ash, four of which are common to both species. Synthetic copies of these VOCs elicited as much oriented upwind flight in mated female C. fraxinella as green and black ash seedlings but did not elicit contact with the VOC lure. Lures do not attract more female C. fraxinella than unbaited control traps in field experiments. These experiments lay the foundation for further development of semiochemical lures based on host VOCs to monitor and potentially control populations of C. fraxinella. Apanteles polychrosidis Vierek (Hymenoptera: Braconidae), is identified here as the dominant parasitoid of C. fraxinella in its expanded range. It exhibits protandrous adult emergence and adults mate soon after females emerge. The remainder of the parasitoid complex affecting C. fraxinella in Edmonton is, in order of parasitism rate, Diadegma Förster (near D. fenestrale (Holmgren)) (Hymenoptera: Ichneumonidae), three Sympiesis Förster species (Hymenoptera: Eulophidae) (S. sericeicornis (Nees von Esenbeck), one near S. viridula (Thomson) and one unknown Sympiesis species, and Pteromalus phycidis (Ashmead) (Hymenoptera: Pteromalidae). Of these parasitoids, only A. polychrosidis is present in numbers high enough to control populations of C. fraxinella. Parasitism rate by A. polychrosidis of C. fraxinella on black ash is higher than on green. Parasitism is positively dependent on C. fraxinella density on black ash but is negatively density dependent on green ash. Apanteles polychrosidis exhibits differential attraction to the VOCs of each ash species which may mediate the differential parasitism response. In olfactometer experiments, A. polychrosidis use host location cues induced by feeding damage on black ash but not on green ash. Thirteen ash VOCs are detected by the antennae of A. polychrosidis.