Meikle, W. G. | bioRxiv Science

bioRxiv2020

Sublethal concentrations of clothianidin affect honey bee colony behavior and interact with landscapes to affect colony growth

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.

ecology↗

bioRxiv2018

Effects of exposure to sublethal concentrations of methoxyfenozide on honey bee colony activity and thermoregulation

Methoxyfenozide is an insect growth regulator (IGR) commonly used in agricultural to simultaneously control pests and preserve beneficial insect populations; however, its impact on honey bees in not fully understood. We conducted field and laboratory experiments to investigate bee health in response to field-relevant doses of this pesticide. Significant effects were observed in honey bee colony flight activity and thermoregulation after being treated with methoxyfenozide. Data collected indicated that hives fed 500 ppb methoxyfenozide treated pollen patty had: 1) a significantly reduced rate of daily hive weight loss due to forager departure at the start of the colonys daily activity; 2) the end of the colonys daily activity delayed by 17-21 minutes compared to Control; and 3) higher temperature variability during the winter. Colonies in the 125 ppb treatment group had fewer differences with the Control group, but did show a delay in the foraging end time by 30-46 minutes compared to the Control. Bee colony metrics of adult bee mass and brood surface area, and individual bee measurements of head weight, newly-emerged bee weight, and hypopharyngeal gland size were not significantly affected by the methoxyfenozide exposure levels of our experiments. An experiment conducted using the same treatment groups in the spring resulted in fewer differences among groups than did the experiments conducted in the fall. Analyses of methoxyfenozide concentrations in the treatment patty, wax, and bee bread showed that: 1) observed methoxyfenozide concentrations were about 18-60% lower than the calculated concentrations; 2) no residues were observed in wax in any treatment; and 3) methoxyfenozide was detected in stored bee bread in the 500 ppb treatment, at concentrations about 1-2.5% of the observed concentration for that treatment. These results suggest that there may be significant effects on honey bee colony behavior (and possibly health) in the field that are difficult to detect through traditional hive inspections and individual metrics.

zoology↗