Proportion of commodity crop pollens and pesticide contamination in honey bee diets in two different landscapes

Abstract

Honey bees are the most important managed pollinators in commercial agriculture. Large irrigated mixed agricultural landscapes in the mid-south United States can be vital to maintaining commercial honey bee operations during times of prolonged nectar dearth, even if those crops are not dependent on bee pollinators. Severe declines in bee populations have generated concerns about the relationship of pesticide-treated seeds and crops and the health of honey bees. To investigate the role of pollen from seed-treated crops as a component of honey bee diet and pesticide contamination in pollen diet of honey bees from agricultural and urban landscapes, we monitored honey bee colonies in both agricultural and urban areas. Pollen collection began in mid-March, before seed-treated crops were planted, and continued through the end of August, after crops had ceased blooming. Pollen samples from returning bees were identified to determine the botanical origin of the bees’ pollen diet, and were also analyzed for pesticide contamination. Honey bees in the agricultural landscape visited crop sources only during the seasonal period of natural nectar dearth, when other wildflower sources were limited, and they encountered acutely toxic pesticide residues (above LD50) during this period. These bees also encountered toxic levels of herbicide on multiple occasions throughout the season, in pollen from non-crop plants. Bees in the urban area were also exposed to toxic levels of insecticides on several occasions. Urban bees were exposed to herbicides throughout the season, but not at concentrations approaching acute toxicity. Simultaneous exposure to multiple pesticides occurred at both sites on multiple occasions. The results underscore the need to conserve areas of habitat and forage for both wild and managed pollinators within both agricultural and urban landscapes.