TOXICITY AND RESIDUAL ACTIVITY OF FENVALERATE TO TYPHLODROMUS OCCIDENTALIS (ACARI: PHYTOSEIIDAE) AND ITS PREY TETRANYCHUS URTICAE (ACARI: TETRANYCHIDAE) ON PEAR

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Abstract
Fenvalerate applied at field rates (3.4–13.7 g AI/100 L) to pear foliage in early season remained highly active to the predatory mite Typhlodromus occidentalis Nesbitt for several months until leaf drop. According to leaf disc assays, fresh deposits of fenvalerate caused considerable direct mortality but most of the later mortality was apparently caused by repellency of the residue and subsequent mite departures. Fenvalerate applied to the bark lost its contact activity more quickly than on foliage. In contrast, adult female Tetranychus urticae Koch suffered no mortality when exposed to leaf deposits, but at high dosages of fenvalerate egg laying was temporarily reduced. In slide-dip tests fenvalerate was about 5 times more toxic to T. occidentalis than to T. urticae (LC50's of 1.21 and 6.74 g AI/100 L, respectively). Our data suggest that because of the persistence of fenvalerate and the high sensitivity of T. occidentalis to this compound this predatory mite would not be able to reestablish after foliar fenvalerate applications and provide biological control of phytophagous mites.