Abstract
Honey bee colonies were exposed to sublethal concentrations (5 and 20 ppb) of clothianidin in sugar syrup, while control colonies were fed syrup with no pesticide. In addition to standard colony assessments of adult bees and brood, hive weight and internal temperature were monitored on a continuous basis at all sites. Experiments were conducted twice in Arizona, in successive years at the same site, and once in Mississippi, to examine the concomitant effects of weather and landscape. Adult bee masses at the Arizona site were significantly affected by clothianidin concentration. Newly-emerged bee dry weights, measured only at the Arizona site, were significantly lower for colonies fed 5 ppb clothianidin compared to the other groups. CO2 concentration, also only measured at the Arizona site, was higher in colonies fed 20 ppb clothianidin. Neither daily hive weight change nor colony thermoregulation were affected by clothianidin exposure. The Mississippi site had higher rainfall, more diverse land use, and a different temperature regime, and bee colonies there did not show any effects of clothianidin. These results suggest that bee colonies in more stressful environments, such as the Sonoran desert of southern Arizona, are affected more by clothianidin exposure than colonies at sites with higher rainfall and more forage. Clothianidin was also found to be, like imidacloprid, highly stable in honey in the hive environment at least over several months. These results also showed that CO2 concentration within the hive is potentially valuable in measuring the effects of stressors on bee health.
