Abstract
Leafrollers can experience high levels of indigenous parasitism in organically managed apple orchards and the augmenta- tive release of specific parasitoid species to suppress these secondary pests may be advantageous in orchards converting to non- chemical pest management. Caged and uncaged releases of two ichneumonid (Apophua simplicipes (Cresson) and Glypta variegata Dasch) and two braconid (Macrocentrus linearis Nees and Apanteles polychrosidis Viereck) koinobiont endoparasitoids of the obliquebanded leafroller, Choristoneura rosaceana (Lepidoptera: Tortricidae) on host-infested potted apple trees were conducted to assess the parasitoids' abilities to find and successfully parasitize sentinel hosts under orchard conditions. Seasonal timing of the trials varied for each parasitoid species, based on their relative performance under simulated summer/fall conditions in laboratory tri- als. After the release of five or fifty parasitoid females, the mean percent parasitism of leafroller larvae collected from infested trees ranged from 0 to 75% depending on the parasitoid species involved. Although caged releases tended to increase the percentage of live parasitized hosts in release treatments, uncaged releases provided a more realistic assessment of the parasitoid's ability to seek and find hosts within an infested area over a longer period. Release of the large, solitary A. simplicipes, had the most significant impact on the host population density.
Highlights
Apple orchards in the interior of British Columbia, Canada are part of an area-wide sterile male codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae) release program (Dyck & Gardiner, 1992)
If the parasitoids were responding in a direct host density dependent fashion when released in the caged or uncaged trees, it would be within the theoretical capacity of 50 females of each parasitoid species released to parasitize all hosts
Any of the four parasitoid species may not have been responding to kairomones resulting from obliquebanded leafroller larvae feeding on apple foliage and this aspect of the trials needs to be better understood
Summary
Apple orchards in the interior of British Columbia, Canada are part of an area-wide sterile male codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae) release program (Dyck & Gardiner, 1992). Where this biological control strategy has been successful, there has been a substantial reduction in the use of codling mothtargeted chemical insecticides that suppressed other susceptible secondary orchard insects such as leafrollers (Lepidoptera: Tortricidae). Apophua simplicipes (Cresson), Glypta variegata Dasch (Hymenoptera: Ichneumonidae), Macrocentrus linearis Nees and Apanteles polychrosidis Viereck (Hymenoptera: Braconidae) are common indigenous, koinobiont endoparasitoids of early-instar obliquebanded leafroller larvae in organically managed orchards in the southern region of the above codling moth area-wide control program (Cossentine et al, 2004a). All of the above parasitoids, except possibly the G. variegata, are bivoltine as they have been recorded to emerge from the summer leafroller generation (Cossentine et al, 2004a)
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