6.2. Mortality and poisoning signs in honey bee queens
Most of the information on pesticide impacts on colonies comes from experimental protocols performed in field conditions, protocols not focused on the effects of pesticides on the queens. In such studies, standardized colonies are fed with sugar syrup or pollen patties contaminated with different pesticides at different concentrations. The administration of contaminated food was regularly repeated over a period of several weeks on colonies in the field.
When pollen patties were contaminated with micro-encapsulated methyl-parathion (Penncap-M), an organophosphate insecticide, and given to colonies in field conditions, Stoner and Wilson (1983) noticed that queens were superseded or died more frequently in the treated groups than in untreated ones (43.3 % versus 25 %, respectively), without clear relation between concentration and queen problems. When colonies were fed with sugar syrup contaminated with 10 ppm dimethoate, another organophosphate insecticide, Stoner et al. (1983) observed that queens died but were not replaced.
Two hypotheses involving the nurse bees were proposed to explain the queen death. The toxin, carried by the sugar syrup, contaminated the crop of the workers and particularly that of the nurse bees. When they offered the glandular secretions to the young larvae or to the queens, they regurgitated contaminated matters at the same time (Davis and Shuel, 1988). Consequently, the queen can be poisoned directly (fed contaminated food) or the queen can reject the contaminated food and suffer from malnutrition. Both hypotheses could result in a situation where the queen drastically decreases egg production. A reduction in egg production generally triggers queen elimination (supersedure) by worker bees. In the case of carbofuran, a carbamate insecticide (Stoner et al., 1982), heavy losses of young bees by poisoning occurred.