Effects of Fenvalerate and Permethrin on Tetranychus urticae Koch (Acari: Tetranychidae) Dispersal Behavior 1

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Abstract
The effect of synthetic pyrethroids on the dispersal behavior of the twospotted spider mite, Tetranychus urticae Koch, was studied. Fifteen female mites were placed on each of 28 ‘Henderson’ lima bean plants and allowed to migrate to the lower leaf surfaces. Two pyrethroids (fenvalerate and permethrin), an organophosphorous insecticide (phosmet), and a water control were each applied to seven different leaf surface combinations. Mite location relative to pretreatment location was noted and recorded at 24 h posttreatment. Experiments were conducted under laboratory light at 24 ± 1.5°C and 25 ± 2% relative humidity. Distinct differences in dispersal response were found between treatments in regard to location of spray application and in materials applied. Mites dispersed from treated areas to untreated areas in response to pyrethroids, whereas no dispersal response was shown by mites on surfaces directly sprayed with either phosmet or the water control. Movement was minimal where mites were not on surfaces in direct contact with spray materials. Disruption of feeding and changes in habitat selection were also noted by mites in response to pyrethroids. Of the two pyrethroids, fenvalerate had the more severe and lasting effect on mite behavior.