Relationship between field efficacy and laboratory estimates of susceptibility to cyhexatin in populations of European red mite (Acari: Tetranychidae)
Welty, C. | Reissig, W.H. | Dennehy, T.J. | Weires, R.W.
The relationship between field and laboratory estimates of susceptibility to cyhexatin was studied for 2 yr in populations of European red mite (ERM), Panonychus ulmi (Koch), in commercial apple orchards. Field efficacy, expressed as reduction in cumulative mite-days in treated plots relative to untreated plots, was compared with mortality of field-collected ERM exposed to cyhexatin residues in 24-h leafless bioassays. In 1986, population susceptibility to cyhexatin based on two early-season applications in field trials was similar to that derived from laboratory bioassays for 12 of the 14 orchard populations that were assessed. In 1987, bioassay response of six orchard populations was compared with the efficacy of one versus two cyhexatin applications and with early-season versus summer applications of cyhexatin. Population susceptibility as determined by efficacy of early-season treatments was in agreement with susceptibility in bioassay for four of six populations tested. Summer treatments were less effective than early-season treatments and did not reflect bioassay estimates of susceptibility as well as early-season treatments did. Control was better than expected in several cases. It was concluded that predictions of field efficacy cannot be based on laboratory bioassays alone; mite population dynamics and operational factors related to the cyhexatin application and orchard management also must be considered.
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