Sublethal effects of pesticide residues in honey bee comb on worker honey bees (Apis mellifera L.)

European honey bees, Apis mellifera L, are important agricultural pollinators at risk of pesticide exposures. Colonies can be exposed to in-hive pesticides used to control bee pests, such as mites. Foraging bees are also at risk of exposure to various agricultural pesticides that further contaminate the colony and other nest-mates. Acute poisoning kills the entire colony or cause major losses of workers and obvious damage to brood. However, sub-lethal effects can result in learning and memory impairment, reduced longevity, and or other effects not readily evident. One research objective was to survey the pesticide load in brood combs, sampled from Pacific Northwest beekeeping operations, to better understand the level of pesticide contamination bees are exposed to in the field. Another objective was to examine the sub-lethal effects of pesticide residues on the overall health of immature and adult worker bees. We compared growth and development of worker brood reared on combs from untreated colonies and combs from colonies treated with acaricides. Mortality was recorded at each developmental stage from egg to emerging adult. Adult bees from each treatment were observed and compared for differences in longevity, age polytheism, and susceptibility to other pathogens, such as Varroa destructor mites and Nosema ceranae (Microsporidia) spores. These comparisons provide useful information for beekeepers and scientists interested in sub-lethal effects of pesticides on honey bees and the potential link between pesticide load and the phenomenon, causing major colony losses in the U.S. since 2006, known as colony collapse disorder.