Lethal and sublethal effects of thiamethoxam, a neonicotinoid molecule, on colony performance of A. mellifera

Among insect pollinators, honey bees, Apis mellifera (Hymenoptera: Apidae), are universally acknowledged, most important managed pollinators that also provide honey production. In recent years, neonicotinoids are widely used against a broad spectrum sucking pests. However, they also pose a major threat to the beekeeping industry. The present study aimed to quantify the impact of thiamethoxam, a second-generation, broad-spectrum neonicotinoid on foraging behavior, colony performance, and survival of Apis mellifera L. in mustard crop under semi-field (cage) and field conditions. Under semi-field conditions, the foraging activity of A. mellifera on mustard bloom reduced significantly on the 2nd day after spray of thiamethoxam as compared to pre-count and control. Significant decrease in brood area (7th to 21st day), nectar stores (7th to 28th day), and pollen stores (7th to 21st day) were also recorded after the spray. The bee mortality under semi-field conditions was significantly higher on the 1st and 2nd day after spray in comparison to control. Under field conditions, average bee activity remained statistically low up to the 12th day after spray on mustard bloom in comparison to pre-count and control. The effect of thiamethoxam under field conditions was less pronounced for bee mortality and colony parameters. Based on LD₅₀, thiamethoxam was proved toxic to adults and larvae of A. mellifera.