Biocontrol of Pests of Apples and Pears in Northern and Central Europe: 2. Parasitoids

The parasitoids of arthropod pests of apple and pear in northern and central Europe and their use as biological control agents are reviewed. The review demonstrates that apple and pear pests are host to a large and varied parasitoid fauna. All important pests are known to be host of parasitoids, but many parasitoids play only a minor part in regulating populations of their host. However, many parasitoid species are important natural enemies and some effectively regulate pest populations in unsprayed and/or commercial (insecticide sprayed) apple or pear orchards either individually or as part of parasitoid guilds. Exploitation/fostering of existing populations of parasitoids has been demonstrated to be an effective or partially effective approach for natural control of several important pest species. Important examples include natural regulation of the apple sawfly by Lathrolestes ensator and Aptesis nigrocincta, of the summer fruit tortrix moth by Colpoclypeus florus and Teleutaea striata, of leaf midges by Platygaster demades, of woolly aphid by Aphelinus mali and of leaf mining moths by guilds of parasitoid species. Introduction of parasitoids is an alternative approach to the exploitation of parasitoids already present in the orchard. This approach has been little explored and its success rate has been low, mainly confined to the control of non-indigenous pests by introducing parasitoids from their native region. Mass production methods for parasitoids are difficult and costly and are likely to be economic only where long-term populations can be established. Even where low cost mass culture techniques are developed, the degree of control may not be high enough to prevent economic pest damage as demonstrated by negative results with mass release of Trichogramma egg parasites for control of tortricids in orchards. Suitability of the orchard habitat is recognized as crucial to the success of individual parasitoids. Key requirements are adequate populations of the pest(s) and/or alternative hosts, suitable shelter, overwintering sites or food sources and avoidance of harmful effects of pesticides. Many species are highly sensitive to broad-spectrum insecticides, especially in the adult life-stage. Avoiding the harmful affects of insecticides is crucial to successful exploitation. The use of insecticides needs to be avoided, either altogether or at crucial times in the parasitoids' life cycle, or less harmful alternatives need to be used. Numerous parasitoids could potentially be exploited as biological control agents but hitherto have received little attention because little is known about them and/or because they are sensitive to broad-spectrum pesticides and are thus virtually absent from commercial orchards. The aim of future studies should be to develop effective strategies for establishing equilibria between important pests and their parasitoids, with pest damage rarely exceeding the economic threshold.

Keywords:

• Arthropod
• Aphid
• Blossom Weevil
• Codling Moth
• Fruit
• Insecticide
• Integrated Pest Management
• Leaf Hopper
• Leaf Midge
• Natural Enemies
• Orchard
• Pesticide
• Parasite
• Pome
• Fruit
• Scale
• Sucker
• Tortrix
• Winter Moth
• Woolly Aphid
• Sawfly