Fenvalerate‐induced aerial dispersal by the twospotted spider mite

Abstract

AbstractIn response to residue of a sublethal dose of the synthetic pyrethroid fenvalerate, twospotted spider mites, Tetranychus urticae Koch, exhibited an aerial dispersal behavior in addition to a previously documented walk‐off response. The magnitudes of the two responses were positively correlated, although the peak incidence of aerial dispersal behavior occurred 1.3 h after the peak of walk‐off. Mite response was the same on treated and untreated non‐feeding surfaces (31.2 and 36.2% walk‐off, 58.4 and 55.6% aerial, respectively), suggesting that fenvalerate did not induce dispersal by direct irritancy. Response on treated leaf disks (40.6% walk‐off, 41.6% aerial) was similar to that on the non‐feeding surfaces, but few mites exhibited dispersal behaviors on untreated leaf disks (7% walk‐off, 0% aerial). The difference between mite dispersal from treated and untreated leaf disks was attributed to a direct antifeedant effect of fenvalerate, which was thought to hasten desiccation by preventing imbibition. This hypothesis was supported by experiments in which mites on non‐feeding surfaces responded more rapidly and in greater numbers when held at 10% relative humidity than at 95% r.h. regardless of fenvalerate residues on the substrate. The relationship among the different types of fenvalerate‐induced mite dispersal behavior is discussed.