Sub-lethal effects of pesticide residues in brood comb on worker honey bees (Apis mellifera L.)

Judy Yu Wu

The European honey bee, Apis mellifera L., is an important pollinator for many agricultural crops. The United States Department of Agriculture estimates one-third of our diet comes from insect-pollinated plants. Of that, 80% are pollinated by honey bees (Thapa, 2006 J. Inst. Agric. Anim. Sci 27:1-23). Unfortunately, honey bees are faced with challenges including mites, microsporidia, viruses, poor nutrition and exposure to pesticides. Miticides have been used since the late 1980's in the U.S. to treat the problematic mite Varroa destructor (Varroidae) in bee colonies. Honey bees are often exposed to high frequent doses of miticides as beekeepers seek to counter the mite's rapidly developing resistance to chemical treatments (Elzen et al.,1999 Apidologie 30: 17-19; Elzen et al. 2000 Apidologie 31: 437-441). In addition, exposure to agrochemicals occurs during flight and foraging activities (Rortais et al., 2005 Apidologie 36: 71- 83). Returning foragers may further contaminate nest-mates and resources. Current risk assessments for pesticides examine lethality of adult bees to a single active ingredient in a laboratory setting. However, sub-lethal effects of pesticide on immature bees and effects from mixtures, used in the field, are not routinely used to assess the toxicity of pesticides during the registration process. This study examined pesticide residue contamination found in brood comb and investigated sub-lethal effects of pesticide residues on larval survivability, adult longevity, and susceptibility to Nosema ceranae (Nosematidae) infection. Worker bees were reared in contaminated comb, containing high levels of pesticide residues, or in relatively "clean" comb within the same colony. Comparisons of survivability from egg to adult and larval development rates yielded lower survivability and evidence of delayed development for bees reared in contaminated combs. Adult longevity was. On average, four days shorter for bees reared in contaminated combs compared to control bees. In a field experiment, a significantly higher proportion of bees reared in contaminated comb were infected with Nosema ceranae spores at a younger age and with higher infections than bees reared in clean comb. This suggests early exposure to pesticide residues during development can have serious effects on larval survivability and subtle delayed effects in the adult stage.

Sub-lethal effects of pesticide residues in brood comb on worker honey bees (Apis mellifera L.)

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