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Natural Enemies/Biological Control in Deciduous Fruit Crops
Natural enemies and environmental factors limit populations of insect and mite pests in natural ecosystems. When natural enemies are killed by human's actions in any habitat or when pests are introduced to new habitats without their natural enemies, natural control often fails and results in pest outbreaks. Biological control of pest species by predators, parasitoids, and pathogens has been a cornerstone of IPM since its inception. It has been difficult to utilize the full potential of biological control in tree fruit and other crops that receive periodic sprays of broad-spectrum pesticides and/or have high-quality standards. The best pest targets for biological control in tree fruits are generally the secondary foliage-feeding pests that do not cause direct fruit injury (i.e., mites, aphids, and leafminers). Populations of pests that feed directly on the fruit (i.e., codling moth, Oriental fruit moth, and plum curculio) generally cannot be tolerated at levels high enough for biological control agents to reproduce.
While biological control is often thought of as a biopesticide where a single species of beneficial arthropod is released or conserved, the best results are most often achieved where a complex of many species of natural enemies, including predators and parastioids, each contribute to reducing pest populations at different times of the season and on different developmental stages. While the development of pesticide resistance (mainly to organophosphates) has occurred in Stethorus punctum, the black ladybeetle predator, and several species of predatory mites, such resistance is generally much slower to develop in beneficial arthropods. Resistance to pesticides in tree fruit pests is generally through enzymatic degradation of the pesticide within the pest's body. Plant-feeding pests developed these enzymes before the use of pesticides to degrade the toxic chemical defenses of their host plants. Many predators/parasitoids do not possess these multipurpose enzymes and hence are less able to deal with pesticides. Thus, the biological control potential of the vast majority beneficial arthropods is not realized unless they develop resistance to pesticides, no pesticides are used, or only pesticides that are selective and nontoxic to these arthropods are used.