Effect of thiamethoxam on the survival of brood in Apis mellifera L. colonies placed in mustard fields.

Honey bees come under stress if thiamethoxam (a neonicotinoid insecticide) is used on their forage crops. The lethal and sub-lethal effects of this insecticide have largely been documented on foraging bees in comparison to the non-foraging stages especially the immature stages. Hence, the present study, to know the effect of thiamethoxam (25 and 50 g a.i. ha⁻¹) on the brood of Apis mellifera colonies in mustard was conducted. Brood index, compensation index, and brood termination rate were calculated for the brood area (2 sq. inch) selected at two time intervals i.e. at the time of spray (D0) and seven days after that (D7). Brood index for the brood selected at D7 of thiamethoxam applied at 25 g a.i. ha⁻¹ was statistically at par with the untreated control i.e. its value at 21 days (1.00 ± 0.00-4.48 ± 0.04) was statistically at par with the untreated control (1.00 ± 0.00-4.66 ± 0.01). However, in other treatments viz. brood selected at D0 in thiamethoxam applied at 25 g a.i. ha⁻¹ and at D0 and D7 in thiamethoxam applied at 50 g a.i. ha⁻¹, significant brood mortality was recorded at the end of the brood cycle. Compensation indices and brood termination rates also showed similar effects. Overall, it is concluded that thiamethoxam at the recommended dose i.e. 25 g a.i. ha⁻¹ did not affect the brood which was reared 7 days after the application. [ABSTRACT FROM AUTHOR]