Pesticide Exposure During Development Does Not Affect the Larval Pheromones, Feeding Rates, or Morphology of Adult Honey Bee (Apis mellifera) Queens

Abstract

Recent work demonstrated that honey bee (Apis mellifera L.) queens reared in pesticide-laden beeswax exhibit significant changes in the composition of the chemicals produced by their mandibular glands including those that comprise queen mandibular pheromone, which is a critical signal used in mating as well as queen tending behavior. For the present study, we hypothesized that pesticide exposure during development would alter other queen-produced chemicals, including brood pheromone in immature queens, thus resulting in differential feeding of queen larvae by nurse workers, ultimately impacting adult queen morphology. We tested these hypotheses by rearing queens in beeswax containing field-relevant concentrations of (1) a combination of tau-fluvalinate and coumaphos, (2) amitraz, or (3) a combination of chlorothalonil and chlorpyrifos. These pesticides are ubiquitous in most commercial beekeeping operations in North America. We observed nurse feeding rates of queen larvae grafted into pesticide-laden beeswax, analyzed the chemical composition of larval queen pheromones and measured morphological markers in adult queens. Neither the nurse feeding rates, nor the chemical profiles of immature queen pheromones, differed significantly between queens reared in pesticide-laden wax compared to queens reared in pesticide-free wax. Moreover, pesticide exposure during development did not cause virgin or mated adult queens to exhibit differences in morphological markers (i.e., body weight, head width, or thorax width). These results were unexpected given our previous research and indicate that future work is needed to fully understand how pesticide exposure during development affects honey bee queen physiology, as well as how various adult queen quality metrics relate to each other.

Methoxyfenozide has minimal effects on replacement queens but may negatively affect sperm storage

“…Queens exposed to high levels of the miticides Amitraz, coumaphos, tau-fluvalinate, and the pesticides chlopyrifos and chlorothalonil not only experienced reduced oviposition rates but also recruited smaller retinue sizes and had lower contents of QMP pheromone component critical for queen retention. These pesticides did not affect worker rearing of new queens in a subsequent study, highlighting the complexity of pesticide effects on developing queens (Walsh et al 2021). In this study, MEOF-treated queens did not have an altered QMP/QRP pheromone profile that reflected reduced sperm storage.…”

“…Developmental exposure to the neonicotinoids thiamethoxam and clothianidin resulted in fewer queen matings with drones than unexposed queens (Forfert et al 2017). By contrast, Walsh et al (2021) found that developing queens exposed to amitraz, tau-fluvalinate and coumaphos, or chlorothalonil and chlorpyifos in wax either did not differ in their mating frequency or had higher mating frequencies (amitraz). Rangel and Tarpy (2015) found that queens reared on taufluvalinate and coumaphos-contaminated wax had higher mating frequencies than unexposed controls.…”

“…Sperm storage in queen spermathecae, which requires significant physiological support (Collins et al 2004b), has also been shown to be negatively impacted by certain agrochemicals but not others. Developmental exposures to the IGR fenoxycarb, the miticides tau-fluvalinate, coumaphos, and amitraz, the neonicotinoid thiamethoxam, the organophosphate chlopyrifos and chlorothalonil have all resulted in lower sperm viability or reduced queen viability in developing queens (Thompson et al 2005;Gajger et al 2017; Rangel and Tarpy 2015; but see Walsh et al 2021). Effects of pesticide contaminants on developing queens appear to be complicated but observable in field colonies.…”

Transcriptomic analysis of the honey bee (Apis mellifera) queen brain reveals that gene expression is affected by pesticide exposure during development

“…Most recently, work in our laboratory showed that exposure of queen larvae during development to wax containing either a combination of tau -fluvalinate and coumaphos, or with amitraz alone, affected many aspects of worker behavior and queen physiology [ 25 , 26 , 72 ]. For example, we found that queens exposed to amitraz during development exhibited higher mating frequency than queens reared in pesticide-free beeswax [ 25 ].…”

“…Once mating status was confirmed and the queens had been laying a minimum of four weeks, the queens were sacrificed and maintained at -80°C until dissection. Other tissues from the same queens, including the mandibular glands, the spermathecae, and the ovaries, were used for three separate but related studies [ 25 , 26 , 72 ].…”