Organotin resistance in tetranychus urticae koch on pear : components and their integration for resistance management Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/mk61rm47z

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  • Reversion of resistance to the organotin (OT) acaricide cyhexatin was documented for the twospotted spider mite, Tetranychus urticae (Koch), by laboratory isolation of a field resistant colony. After 22 generations of no selection the colony reverted back to susceptible. Studies were conducted in 1985 and 1986 on susceptible and resistant T. urticae to test whether relative fitness differences were responsible for OT reversion. Susceptible colonies had significantly shorter developmental times. In addition, a field susceptible strain had a higher female to male sex ratio, and percent survival (egg to adult) than the field resistant strain. These differences are assumed to contribute to reversion in laboratory isolated resistant colonies. The effect of immigration on organotin resistance was also investigated. An immigration (dilution) experiment revealed that dilution of resistance allowed a moderately resistant colony to revert to susceptible in ca. three generations. In the field several tactics for managing OT resistance were investigated. Formulation differences (i. e. wettable powder verses flowable) of cyhexatin and fenbutatin oxide were found to have an effect on efficacy. In addition cyhexatin efficacy was improved when organotin selection to a population of T. urticae from southern Oregon pear was reduced by substitution of an acaricide to which mites were not cross-resistant. Abamectin (avermectin B1) was substituted for cyhexatin in 1984 and 1985 in an orchard block harboring resistant mites in 1983. After two years of relaxed selection a standard organotin treatment was reapplied to the abamectin treated block. Better control was achieved with cyhexatin in the abamectin block than in a block that had been continuously treated with cyhexatin over the same two year period. This suggests that reducing selection pressure, by substituting the noncross-resistant compound, allowed resistance to revert in the field. These results suggest a possible mechanism by which organotin resistance in T. urticae may be managed.
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  • description.provenance : Submitted by Kirsten Clark (kcscannerosu@gmail.com) on 2013-06-03T17:18:01Z No. of bitstreams: 1 FlexnerJohnLindsey1988.pdf: 885955 bytes, checksum: 7ca5f4abac1254ff8cdfdd73592d1c4d (MD5)
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