Methylene Blue Alleviates Thiamethoxam-Induced Toxicity in Honeybee Larvae by Activating Dihydrolipoyl Dehydrogenase

The extensive utilization of TMX, a substance characterized by its high toxicity towards honeybees, has exerted a deleterious influence on the employment of neonicotinoid insecticides and the proliferation of bee colonies. However, there is a lack of effective solutions to mitigate the toxicological impact of neonicotinoid insecticides on bees. The present study proposes a method of using MB to alleviate TMX poisoning in honeybee (<i>Apis mellifera ligustica)</i> larvae. The results demonstrated that when bee larvae ingested MB at a concentration of 0.32 mg·L^-1, the mortality rate of larvae could be reduced from 47.2% to 25.0%. Transcriptome analysis identified the honeybee dihydrolipoyl dehydrogenase (<i>AmDld</i>) gene as one of the main genes involved in the function of MB. <i>AmDld</i> was highly expressed in larval hemolymph. Its expression levels and enzymatic content were suppressed by either TMX or MB alone but restored by the TMX+MB combination. RNAi-mediated knockdown of <i>AmDld</i> decreased AmDld content and increased larval mortality under the TMX+MB co-treatment from 25.0% to 40.6%. This indicated that the TMX+MB combination rescued <i>AmDld</i> levels, thereby alleviating TMX toxicity to bee larvae. The present study has demonstrated that the ingestion of MB by honeybee larvae has the capacity to reduce the toxicity of TMX, a toxic substance, through the action of the <i>AmDld</i> gene. This provides a novel approach to mitigating pesticide poisoning in bees.