Exposure to sublethal concentrations of methoxyfenozide disrupts honey bee colony activity and thermoregulation

Abstract

Methoxyfenozide is an insect growth regulator (IGR) commonly used in agriculture 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 concentrations of this pesticide. Significant effects were observed in honey bee colony flight activity and thermoregulation after being exposed over 9 weeks to supplemental protein patty containing methoxyfenozide. Compared to bee colonies in the control group, colonies fed pollen patty with 200 ppb methoxyfenozide (as measured by residue analysis) had: 1) a significantly reduced rate of weight loss due to forager departure in the morning; and 2) higher temperature variability during the winter. Colonies in the 100 ppb (as measured by residue analysis) treatment group had values between the 200 ppb group and control for both response variables. The dusk break point, which is the time associated with the end of forager return, differed among all treatment groups but may have been confounded with direction the hives were facing. Bee colony metrics of adult bee mass and brood surface area, and measurements of bee head weight, newly-emerged bee weight, and hypopharyngeal gland size were not significantly affected by methoxyfenozide exposure, suggesting that there may be significant effects on honey bee colony behavior and health in the field that are difficult to detect using standard methods for assessing bee colonies and individuals. The second experiment was continued into the following spring, using the same treatment groups as in the fall. Fewer differences were observed among groups in the spring than the fall, possibly because of abundant spring forage and consequent reduced treatment patty consumption. Residue analyses showed that: 1) observed methoxyfenozide concentrations in treatment patty 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 bee bread only in the 200 ppb treatment group, at about 1–2.5% of the observed patty concentration.

Landscape factors influencing honey bee colony behavior in Southern California commercial apiaries

“…Both the start and end of daily activity were significantly earlier for colonies in almonds compared to those in blueberries, but that was likely related to physical characteristics of the apiaries and how the hives were placed. The direction a hive is facing can affect the timing of the daily activity period 25 . Much of the hive weight gain during these periods was probably due to nectar and pollen collection.…”

“…In both August and October, beebread samples from the AG sites had more compounds (13.3 and 11.8, respectively) than either those in CA (11 and 5.8, respectively) or MT landscapes (7 and 8, respectively). These compounds included neonicotinoids, such as imidacloprid, and insect growth regulators (IGRs), such as methoxyfenozide, both of which have been shown to affect thermoregulation in bee colonies 8,25 . Some compounds, such as methoxyfenozide and flupyradifurone, were at high, albeit sublethal levels 29 .…”

“…The same member of the team (EB) estimated all FOB values. The same worker estimated FOB levels in another study in which adult bee masses were measured independently using another method (see 25 ), and the linear regression between that worker's FOB estimates and adult bee masses are provided (see Supplementary File). After visual estimation, both sides of all frames with brood were photographed using a 16.3 megapixel digital camera (Canon Rebel SL1, Canon USA, Inc., Melville, NY).…”

“…The area of sealed brood per frame was estimated later from the frame photographs using either ImageJ software (version 1.47. W. Rasband, National Institutes of Health, USA), or CombCount; 38 this method has been described in other publications (see 8,13,16,25 ). Any colony that had capped brood was included in the study.…”

“…Also, some kinds of exposure may affect honey bee behavior without affecting survivorship. Imidacloprid, which has a comparatively low LD 50 25,33 , had measurable effects on colony behavior at concentrations that had no apparent effect on adult bee longevity 8 raising the question of whether there are compounds with higher LD 50 values but that also affect colony behavior. Incorporating colony-level behavior studies when evaluating novel pesticides may need to be considered.…”