Oral toxicity of Bacillus thuringiensis δ-endotoxin on honey bees

Abstract

The greater wax moth (Galleria mellonella) is a dangerous pest for honey bees. Its presence may inhibit honey bee production, lead to the death of bee colonies and significant damage to beekeeping operations. In this study, we investigated the effects of three different samples of an experimental product based on the bacterium Bacillus thuringiensis strain RCAM 00045 in the form of purified and activated delta-endotoxins on honey bees in laboratory conditions. We studied the acute oral toxicity of these products by feeding bees with sugar syrup containing delta-endotoxin at different concentrations (500 mcg ml, 1000 mcg ml, and 2000 mcg ml) according to the guidelines for environmental evaluation of pesticides and the GOST standard for testing chemical product environmental hazards for honey bees. Carpathian honey bees were used for the experiments. We observed the behavioral reactions of the bees and recorded the presence or absence of any dead bees after exposure to the different concentrations of delta-endotoxin. The data obtained indicated that the doses of δ-endotoxin of 500 mcg ml, 1000 mcg ml and 2000 mcg ml were not toxic to bees when administered orally. The lethal dose (LD₅₀) of the substance when determining the oral toxicity was above the value of 20 mcg per bee, and the lethal concentration (LC₅₀) was above 2,000 mcg ml. Natural insignificant mortality of bees and the absence of changes in their behavioral reactions allowed concluding that the drug did not pose a threat to bees at these concentrations. The data from the study of the experimental product against wax moth regarding its toxicity were necessary to justify the measures to control wax moth infestation and protect bees against poisoning.