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Stability of Dicofol Resistance in Populations of European Red Mite {Acari: Tetranychidae} on Apples in Southern Ontario

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Fluctuations in levels of resistance to dicofol in populations of European red mite, Panonychus ulmi (Koch), from several orchards with different frequencies of resistant individuals were compared with responses of laboratory colonies established from the same sites. Considerable variability in responses occurred in observations spaeed over 2 yr, but the frequency of dicofol-resistant individuals in these populations did not decline in the absence of selection pressure. Laboratory colonies reared through 32 generations displayed relatively constant resistance frequencies, suggesting that dicofol resistance is stable for a time equivalent to at least 3 yr in the field.

Relative fecundities of mites resistant and susceptible to dicofol were examined by comparing the number of eggs laid by females from intra- and interstrain crosses, as well as the percentage hatchability, percentage survivorship, and sex ratio of the resulting progeny. Females from a 12-yr-old susceptible laboratory colony laid more eggs than females from a more recently established susceptible colony and than females from two colonies resistant to dicofoi. Resistant and susceptible mites did not differ for any of the other parameters examined. It is concluded that the absence of a reproductive detriment is a major factor in the apparent stability of resistance to dicofol in these mites. Implications of these findings for management of dicofol resistance in P. ulmi are discussed.

Document Type: Research Article

Publication date: June 1, 1992

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  • Journal of Economic Entomology is published bimonthly in February, April, June, August, October, and December. The journal publishes articles on the economic significance of insects and is divided into the following sections: apiculture & social insects; arthropods in relation to plant disease; forum; insecticide resistance and resistance management; ecotoxicology; biological and microbial control; ecology and behavior; sampling and biostatistics; household and structural insects; medical entomology; molecular entomology; veterinary entomology; forest entomology; horticultural entomology; field and forage crops, and small grains; stored-product; commodity treatment and quarantine entomology; and plant resistance. In addition to research papers, Journal of Economic Entomology publishes Letters to the Editor, interpretive articles in a Forum section, Short Communications, Rapid Communications, and Book Reviews.
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