Sublethal effects of thiamethoxam soil treatment on the development and reproduction of small hive beetle (Aethina tumida Murray)

Recent studies have shown that very low levels of thiamethoxam, clothianadin and imidacloprid residues in agricultural soil can have negative impacts on reproduction, longevity and abundance of soil-dwelling arthropod species. However, most of these studies have focused on the oral route of insecticide exposure to arthropods, and little information is currently available on contact toxicity to these organisms. The small hive beetle (Aethina tumida Murray, Coleoptera: Nitidulidae) is a globally distributed honey bee pest that completes development from larva to adult in the ground. As the beetle occurs in agricultural environments and does not ingest treated soil, it could potentially serve as a model for research on contact toxicity of neonicotinoids to beneficial arthropods (i.e. ground-nesting bees). In the present study, a commercial thiamethoxam insecticide (Cruiser 5FS) was used as a soil treatment, and several biological parameters were measured upon emergence of adult beetles from the treated soil. Thiamethoxam rates ranged from 25 to 200 ng g^-1, and beetles were exposed for 16 days. Mating pairs were established from each treatment group and provisioned with food and water for two weeks, during which time egg counts were made daily. Results showed that all tested rates of thiamethoxam negatively affected emergence mass, onset of oviposition (days) and reproductive output (eggs laid over time) of small hive beetles when compared to untreated controls.