Parasitism of Winter Moth in British Columbia During Build-up of its Parasitoid Cyzenis albicans: Attack Rate on Oak V. apple

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Abstract
(1) The introduced tachinid fly Cyzenis albicans is thought to be responsible for control of pest populations of the winter moth Operophtera brumata in oak forests in Nov Scotia [Canada] but appears unable to control populations in apple orchards. (2) Field and cage studies were conducted on Vancouver Island, British Columbia, Canada, to determine whether differential oviposition on apple and oak foliage by the fly could account for this difference. (3) Both types of foliage elicited strong oviposition response by Cyzenis in cage experiments. (4) In the field, Cyzenis aggregated its ''attacks'' on oak trees in response to the level of feeding damage by winter moth. Aggregation occurred at all levels of spatial scale measured (among all leaf clusters, among leaf clusters within trees, among trees). (5) Eggs laid on apple foliage showed little or no aggregation at any spatial scale. (6) Despite differences in aggregation of attack, total mortality from parasitism was the same for winter moth populations on both tree species. (7) Implications for successful biological control of winter moth in British Columbia are discussed.