The use of dimethoate as a reference compound in laboratory acute toxicity tests on honey bees (Apis melliferaL.) 1981–1992

Abstract

The contact and oral acute toxicity of technical dimethoate to worker honey bees (Apis mellifera) was determined between May and October for 12 consecutive years, 1981–1992 (63 contact tests and 62 oral tests), using standard laboratory methods. The 24-h LD₅₀ values ranged from 0.11 to 0.26 (mean 0.16) μg a.i./bee for contact toxicity, and from 0.11 to 0.33 (mean 0.18) μg a.i./bee for oral toxicity. The 48-h LD₅₀ values were similar to the 24-h ones, indicating that there were no delayed toxic effects. There were no significant seasonal trends in contact or oral toxicity nor were there any consistent trends over the 12-year period. A comparison of British bees with a strain of New Zealand bees indicated that variability between individual colonies was greater than between the two strains. Published results from studies carried out elsewhere in the UK and in Germany are similar (LD₅₀ values within a factor of about two of the mean values presented here). It is concluded that technical dimethoate is suitable as a reference compound for laboratory toxicity tests with honey bees.