The effect of patch size and persistence of host plants on the developmentof acaricide resistance in the two-spotted spider mite Tetranychus urticae(Acari : Tetranychidae)

Spatial and temporal characteristics of host plants can influence the popul ation biology of the herbivores feeding on them. In this study, I examined the effect of variation in host plant characteristics on the development of acaricide resistance in the two-spotted spider mite Tetranychus urticae, a widely distributed agricultural pest. This investigation examined the geog raphic variation in the degree of resistance to two new types of acaricide, pyridaben and fenpyroximate. From mortality tests at field-level concentra tions of the acaricides, many populations collected from fruit trees and ro ses had a high frequency of resistant individuals for acaricides while almo st all populations collected from herbaceous crops had low frequencies of r esistant individuals. These results, combined with those from a previous al lozyme study, indicate that patch size and persistence of host plants regul ate the population structure of the mites including gene flow between popul ations and, by extension, the development of acaricide resistance.