Effects of acaricides,pyrethroids and predator distributions on populations of <Emphasis Type="Italic">Tetranychus urticae</Emphasis> in apple orchards |
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Authors: | J M Hardman J L Franklin F Beaulieu N J Bostanian |
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Institution: | (1) Atlantic Food and Horticulture Research Centre, Agriculture and Agri-Food Canada, 32 Main Street, Kentville, Canada, NS B4N 1J5;(2) Canadian National Collection of Insects, Arachnids and Nematodes, Agriculture and Agri-Food Canada, Ottawa, ON, Canada, K1A 0C6;(3) Horticulture Research and Development Centre, Agriculture and Agri-Food Canada, 430 Gouin Blvd, St. Jean-sur-Richelieu, QC, Canada, J3B 3E6 |
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Abstract: | We sampled mites in three apple orchards in Nova Scotia, Canada, that had been inoculated with pyrethroid-resistant Typhlodromus pyri and had a history of Tetranychus urticae outbreaks. The objective of this study was to monitor populations of T. urticae and phytoseiid predators on the ground and in trees and to track dispersal between the two habitats. Pesticides were the
chief cause of differences in mite dynamics between orchards. In two orchards, application of favourably selective acaricides
(abamectin, clofentezine) in 2002, coupled with predation by T. pyri in trees and Neoseiulus fallacis in ground cover, decreased high T. urticae counts and suppressed Panonychus ulmi. By 2003 phytoseiids kept the tetranychids at low levels. In a third orchard, application of pyrethroids (cypermethrin, lambda-cyhalothrin),
plus an unfavourably selective acaricide (pyridaben) in 2003, suppressed phytoseiids, allowing exponential increases of T. urticae in the ground cover and in tree canopies. By 2004 however, increasing numbers of T. pyri and application of clofentezine strongly reduced densities of T. urticae in tree canopies despite high numbers crawling up from the ground cover. Another influence on T. urticae dynamics was the distribution of the phytoseiids, T. pyri and N. fallacis. When harsh pesticides were avoided, T. pyri were numerous in tree canopies. Conversely, only a few N. fallacis were found there, even when they were present in the ground cover and on tree trunks. Low numbers were sometimes due to pyrethroid
applications or to scarcity of prey. Another factor was likely the abundance of T. pyri, which not only competes with N. fallacis, but also feeds on its larvae and nymphs. The scarcity of a specialist predator of spider mites in trees means that control
of T. urticae largely depends on T. pyri, a generalist predator that is not particularly effective in regulating T. urticae.
The Canadian Crown's right to retain a non-exclusive, royalty-free licence in and to any copyright is acknowledged. |
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Keywords: | Tetranychus urticae outbreaks Typhlodromus pyri Neoseiulus fallacis Pesticide effects on biological control Generalist and specialist phytoseiids Competition and intra-guild predation |
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