Ovipositional preference and host shifting in the ash leaf coneroller, Caloptilia fraxinella (Lepidoptera: Gracillariidae)/Fraxinus system

The ash leaf-cone roller, Caloptilia fraxinella, (Lepidoptera: Gracillariidae) infests horticultural ash, Fraxinus spp., (Oleaceae) in Canadian Prairie urban forests. Black ash, F. nigra, is the host in its native range and the coneroller has formed a new association with green ash, F. pennsylvanica, during its eleven year invasion of the urban forest. Oviposition only occurs in the presence of host leaflets and female moths prefer to lay eggs on black ash over green ash. Females favor new leaflets over old leaflets as an oviposition substrate regardless of ash species. Although the coneroller prefers black ash leaflets for oviposition, green ash induces stronger host location behaviors in wind tunnel experiments. In addition, larvae develop faster on green ash than black ash. Parasitoid pressure is also less on green than black ash and taken together these data indicate a host shift to green ash in progress.