Rj. Jacobson et al., Response to fenbutatin oxide in populations of Tetranychus urticae Koch (Acari : Tetranychidae) in UK protected crops, CROP PROT, 18(1), 1999, pp. 47-52
Control of spider mites, Tetranychus urticae Koch (Acari: Tetranychidae), i
n protected edible crops in the UK has depended on the combined use of the
predatory mite, Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae
), and the selective acaricide, fenbutatin oxide. However, in recent season
s there has been concern that the chemical has not performed well against a
ll T. urticae populations. This paper reports the results of laboratory-bas
ed tests to determine the response to fenbutatin oxide of five populations
of T. urticae collected from various sources with different histories of ex
posure to the acaricide. There were significant differences in the response
of the mite populations; one appeared to be resistant, one partially resis
tant and three susceptible to fenbutatin oxide. Three of the mite populatio
ns became significantly more resistant following a single exposure to fenbu
tatin oxide but there was evidence that they reverted to being more suscept
ible when the selection pressure was relaxed. The results explain why many
growers have experienced intermittent difficulties controlling T. urticae w
ith fenbutatin oxide for several years without the widespread development o
f complete resistance. (C) 1999 Elsevier Science Ltd. All rights reserved.