Biological control of Tetranychus urticae (Koch) on peppermint by Neoseiulus fallacis (Garman) : density relationships, overwintering, habitat manipulation and pesticide effects Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/vm40xv14p

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  • Several aspects affecting population trends and overwintering of Neoseiulus fallacis (Garman) on peppermint were examined. Neoseiulus fallacis was the most abundant phytoseiid predator mite found in peppermint surveys throughout the western U.S. Results of pesticide exclusion and cage studies showed that N. fallacis controlled Tetranychus urticae (Koch) on peppermint in central Oregon. N. fallacis overwintered in the field mostly in dead peppermint leaves and debris. Augmenting plots with dead leaves increased overwintering survival of N. fallacis while the removal of dead leaves decreased overwintering success. Fall applied carbofuran nearly eliminated N. fallacis, leading to outbreaks of T. urticae the following spring. Fall flaming peppermint fields in central Oregon decreased densities of N. fallacis. By spring, more spider mites were found in flamed fields compared with unflamed fields. More N. fallacis motiles and eggs were found after harvest on prostrate peppermint plants compared to erect peppermint plants. There were no differences detected in the densities of spider mites on prostate compared to erect plants. The net effect of this temporal-spatial asynchrony may be to stabilize the predator-prey interaction. Because predator mites dispersed 7.5 m from unflamed peppermint plots to surrounding flamed areas, providing unflamed refuges for predator mites may reduce the negative impact of fall flaming on spider mite control. Populations of T. urticae collected from western Oregon, central Oregon and Montana were found to be dicofol resistant. Resistance to dicofol in T. urticae and disruption of N fallacis by dicofol may have contributed to increased severity of T. urticae in peppermint. Topical applications of acephate, chiorpyrifos, and oxamyl resulted in 100% mortality to N. fallacis in bean leaf disk bioassays. When applied to mint foliage in cages, acephate, chiorpyrifos, and oxamyl resulted in 43%, 81%, and 50% mortality to N. fallacis, respectively. Application of 2.5 cm of water to cages 30 minutes after pesticides were applied reduced mortality to N. fallacis by 25%. These results suggest that predator avoidance, spray coverage, or other factors may reduce the negative impact of certain pesticides on N. fallacis.
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