Impact of Diflubenzuron on Bombus impatiens (Hymenoptera: Apidae) Microcolony Development

Abstract

Reliance on the honey bee as a surrogate organism for risk assessment performed on other bees is widely challenged due to differences in phenology, life history, and sensitivity to pesticides between bee species. Consequently, there is a need to develop validated methods for assessing toxicity in non-Apis bees including bumble bees. The usefulness of small-scale, queenless colonies, termed microcolonies, has not been fully investigated for hazard assessment. Using the insect growth regulator diflubenzuron as a reference toxicant, we monitored microcolony development from egg laying to drone emergence using the Eastern bumble bee Bombus impatiens (C.), a non-Apis species native to North America. Microcolonies were monitored following dietary exposure to diflubenzuron (nominal concentrations: 0.1, 1, 10, 100, and 1,000 µg/liter). Microcolony syrup and pollen consumption was significantly reduced by diflubenzuron exposure. Pupal cell production was also significantly decreased at the highest diflubenzuron concentration assessed. Ultimately, diflubenzuron inhibited drone production in a concentration-dependent manner and a 42-d 50% inhibitory concentration (IC50) was determined. None of the dietary concentrations of diflubenzuron tested affected adult worker survival, or average drone weight. These data strengthen the foundation for use of this methodology, and provide valuable information for B. impatiens; however, more work is required to better understand the utility of the bumble bee microcolony model for pesticide hazard assessment.

Effects of the neonicotinoid acetamiprid in syrup on Bombus impatiens (Hymenoptera: Apidae) microcolony development

“…Future studies using a foraging arena could help distinguish between effects of acetamiprid on adult behavior and resource requirements of the brood. Our observations of smaller nests resulting in diminished pollen consumption is consistent with previous microcolony assessments wherein toxicants that impact larval growth and development reduced pollen consumption [ 36 , 37 ].…”

“…The organized workers will build nest structures and tend to brood akin to a queenright colony, however, unlike queenright colonies, microcolonies are suitable for large scale experiments. Microcolonies can be evaluated more easily and reliably, thus functioning as a useful experimental format for assessing nest-relevant endpoints that have population-level implications [ 36 ].…”

The Importance of Males to Bumble Bee (Bombus Species) Nest Development and Colony Viability

“…Many studies using this methodology have evaluated brood development. For instance, reduced brood production (reduced numbers of eggs and larvae) has been found to occur with exposure to neonicotinoids [24,66], and chitin synthesis inhibitors [67][68][69]. Another measurement used in microcolony studies, drone production, integrates all aspects of drone growth and development from egg to emergence.…”

“…Some researchers choose to assess drone production rather than brood development since total offspring production is somewhat easier to measure given that bumble bee nest structures are layered, and quantifying brood structures can be challenging. Chemicals found to inhibit brood production also reduce overall drone production such as chitin synthesis inhibitors [69] and neonicotinoids [21]. Other chemicals found to reduce drone production are transgenic plant proteins [25], the ryanoid insecticide chlorantraniliprole [26], acaricides [70], biopesticides [71], the insecticides spinosad and spinetoram [27], and the pyrethroid λ-cyhalothrin [21].…”

“…Studies could be devised to assess pesticide effects on drone behavior (brood tending and foraging). The effects of chronic developmental pesticide exposure on drone development, immune system function and sperm quality could also be studied by provisioning microcolonies with pesticide spiked pollen [34,69]. Critically, pesticide-exposed drones could be used in mating studies to confirm drone reproductive fitness.…”