Sublethal effects of imidacloprid and amitraz on Apis mellifera Linnaeus (Hymenoptera: Apidae) larval development and larval susceptibility to Varroa destructor Anderson & Trueman (Mesostigmata: Varroidae)

Managed honey bee populations have declined dramatically in the United States since 2005. Population decreases have been attributed to a number of causes including, but not limited to, pesticide exposure, parasite vectored pathogens, arthropod bee pests, and stress. Recently, there has been resurgence among researchers to investigate the possibility of pesticide effects. Pesticides of particular interest are the neonicotinoids and varroacides. Therefore, I chose to investigate how doses of two pesticides, imidacloprid and amitraz, affect bee larval development and larval susceptibility to varroa. To test this, I fed bee larvae with diet containing various concentrations of one of the two test pesticides and measured mortality at larval and pupal development as well as several sublethal variables. Secondly, I introduced pesticide treated larvae into varroa infested colonies to determine the number of mites per larva that occur in a treated cell. My results suggest amitraz fed larvae have higher larval mortality at the highest dose administered. Both amitraz and imidacloprid fed larvae had a lower percentage of adults to emerge than untreated larvae. Only imidacloprid treated larvae showed possible sublethal effects. Treated larvae had an increased larval weight at defecation and increased larval development time. There was not enough data to suggest whether or not treatment by imidacloprid or amitraz influences bee brood susceptibility to varroa. Results from my research suggest that even small doses of certain pesticides effect bee brood development, but the effects that these pesticides could have on a colony level are still unclear.