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Conservation of Pholetesor ornigis (Hymenoptera: Braconidae), a Parasitoid of Phyllonorycter blancardella (Lepidoptera: Gracillariidae) in Ontario

The braconid Pholetesor ornigis (Weed) may parasitize 80% of the larvae of the spotted tentiform leafminer, Phyllonorycter blancardella (F.), but parasitism rates vary widely among leafminer generations and among apple, Malus domestica Borkhausen, orchards. Temperature, food, or insecticides could affect the reproductive performance of P. ornigis. All of the insecticides recommended for control of apple insects in Ontario are toxic to adult parasitoids. Of three potential methods for reducing the effects of insecticides on arthropod natural enemies (i.e., the selection and establishment of insecticide-resistant strains, the use of physiologically selective insecticides, and the selective use of broad-spectrum insecticides), only the last method currently has potential application to P. ornigis in Ontario. Two methods of conserving P. ornigis by selective use of broad-spectrum insecticides were evaluated by measuring parasitism in an Ontario orchard. In the first, insecticide sprays were eliminated or timed to avoid adult activity, which was monitored with yellow sticky traps. In the second, the timing of insecticide applications followed a conventional integrated pest management (IPM) program, but insecticides were applied at one-half of the recommended rate. Both methods showed potential for conserving parasitoids when compared with a conventional IPM program. These approaches will require additional evaluation to determine their effect on leafminer density and on the control of the codling moth. Cydia pomonella (L.), and the apple maggot, Rhagoletis pomonella (Walsh).

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