Comparative Morphogenic and Toxicity Studies on the Effects of Pesticides on Honeybee (Apis mellifera L.) Brood

The studies conducted during 2005~06 to evaluate the relative toxicity and amorphogenic effects of imidacloprid and demeton-o-methyl on the honeybee brood (A. mellifera) revealed that both demeton -o-methyl and Imidacloprid were highly toxic to eggs and 1~2 day old larvae at all the concentrations as no eggs or larvae survived. Demeton-o-methyl were also found to be highly toxic to 3~4 and 5~6 days old larvae at recommended concentration resulting in complete mortality of treated larvae. However, at half and one fourth of recommended concentrations larval mortality and number of deformed bees significantly decreased. Imidcaloprid was highly toxic to 5~6 days old larvae at recommended and half of recommended concentrations, resulting in complete mortality of treated larvae. However, at one fourth of recommended concentrations, larval mortality and number of deformed bees significantly decreased. The deformed individuals were discoloured, smaller in size having reduced body weight and other dimensions. Wings were absent or rudimentary. Similarly, Carbaryl proved highly toxic to eggs. At the recommended and half of the recommended concentrations all the eggs in the cells treated with carbaryl died and no cell was capped. However at one fourth of the recommended concentration, mortality was 76.67 percent. 1~2 and 3~4 days old larvae were highly susceptible to the recommended concentration (0.10%). There was 100 per cent mortality of larvae treated with recommended concentration. No capping occurred. However, 5~6 day old larvae were less susceptible to recommended concentration as compared to 1~2 and 3~4 day old larvae. Capping of the cells was also abnormal and emergence occurred on 23 rd day in all the insecticides except endosulfan. Endosulfan was relatively safer to honeybee brood.