A Field Trial to Assess the Effects of a New Pyrethroid Insecticide, WL85871, on Foraging Honeybees in Oilseed Rape

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Abstract
Summary WL85871 (10 and 20g ai ha−1), parathion-methyl (500g ai ha−1) [MEP] and phosalone (1200g ai ha−1), were each applied to large isolated fields (5·3–13 ha) of flowering oilseed rape during peak foraging activity of honeybees (Apis mellifera). No increase in bee mortalities, compared with those in the pre-treatment period, was observed after the applications of WL85871 or phosalone. In contrast, large numbers of dead bees were found following the application of MEP. Foraging activity in the crop declined for a few hours after the application of phosalone and of WL85871 at the lower dose rate. A slightly more pronounced and prolonged decline in foraging activity occurred at the site treated with WL85871 at the higher dose rate. The amount of pollen collected by the bees was adversely affected only by the application of MEP. None of the treatments had any detectable effects on the overall condition of the hives at the end of the season. Concentrations of WL85871 residues in post-treatment samples of dead bees, pollen, honey and wax were either very low or undetectable. Little or no mortality in laboratory bioassay tests was caused by feeding adult worker bees with pollen and honey collected after application from the two WL85871-treated sites. It was concluded that the application of WL85871 to flowering oilseed rape resulted in no adverse effects on honeybees or long-term colony development.