Effects of wetting agent selection on the contact toxicity of a dimethoate formulation to honeybees

摘要

A range of wetting agents are suggested by OECD Guideline 214 for assessing the contact toxicity of pesticides to honeybees. This study aimed to determine the effect of wetting agent selection on the contact toxicity of an EC formulation of dimethoate. A number of wetting agents were used; Triton X100, Tween 20, Igepal, Span 20, Brij 35 and polyoxyethylene W1 all at 1 g/l and the results compared with dimethoate formulation dissolved in acetone. All dilutions were prepared within two hours of use,except Triton X100 and acetone where an additional set of dilutions were prepared 16 hours in advance. All bees were dosed in groups of ten with 3 replicates per dose at dose levels of 0.25, 0.125 and 0.063 mu g a.i. dimethoate/bee. All tests were run concurrently with a wetting agent control (30 bees) to provide data on the toxicity of the wetting agent alone. Mortality was assessed at 4, 24 and 48 hours after dosing and probit analysis performed to determine the 48 hr LD_(50), 95 percent confidence limits and slope of the dose-response. The results of this study are presented and the effects on choice of wetter agent discussed.