Honey Bee (Hymenoptera: Apidae) Foraging During Bloom in Dimethoate-treated Apple Orchards

Abstract

Honey bee ( Apis mellifera L.) reactions to dimethoate (Cygon 400) residues were evaluated following apple grower reports of decreased foraging activity and fruit set subsequent to prebloom dimethoate applications. Data collected in 1981 and 1982 in Adams County, Pa., indicated no reduction of foraging on trees treated 2–18 days earlier with dimethoate at recommended rates (562 g [AI]/ha). No excessive bee mortality was found during the tests, nor was fruit set affected by the prebloom sprays. Selective, small-scale applications made during bloom significantly shortened the duration of foraging trips and decreased the number of flowers visited on treated trees by individual foragers. A testing method using apple branch bouquets, pruned from trees, was devised to measure bee visitation on a per-flower basis. Significantly lower visitation occurred to dimethoate-sprayed bouquets at 2 days after treatment, but not at 3 days after spraying. When blooming bouquets were sprayed in the morning with either a field-rate (as above) or an exaggerated (triple concentration) dimethoate treatment, flowers typically received fewer bee visits throughout that test day.