Posted: February 5, 2021

CPR graduate student Katie Barie profiles a recent paper written by PSU Entomology's own Erin Treanore and Etya Amsalem

Photo by J. Lana Mejias

Photo by J. Lana Mejias

As State College is once again covered with several inches of snow, you may be finding it hard to cope with the wintery conditions. It is no different for bee species living in temperate regions. Bees have to find a way to deal with seasonal snow fall and cold temperatures just like we do. In order to survive this period of harsh environmental conditions some bee species enter diapause. Diapause is an advantageous strategy to circumvent seasonal harsh conditions.

Similar to hibernation, diapause is a period of arrested development and behavior. During this period, bees go dormant and no longer forage, feed, or reproduce.

Though winter dormancy may sound like an appealing long nap, surviving months of dormancy without feeding in cold conditions is physiologically demanding. The stressors and energetic demands on bees during diapause can lead to mortality. As many bee species face population declines, it is important to understand what factors are influential in diapause survival in order to develop conservation strategies.

Recent research by Erin Treanore, an Entomology graduate student at Penn State, examined physiological factors which influence diapause survival in the bumble bee, Bombus impatiens.

As in most bumble bees, this is an annual social bee species, where a single queen establishes a colony in the spring following a winter diapause. These queens initially emerge from their natal colony in late summer or fall and spend a short period mating and accumulating nutrient stores for diapause. Treanore's research in the Amsalem lab examined the impacts of queen age and mass on diapause survival and tested potential mechanisms explaining these impacts. A queen's mass may affect diapause survival because higher mass is indicative of increased nutrient reserves which can be used during diapause. The age at which a queen enters diapause may influence survival because physiological declines (eg. oxidative damage to cells) may occur as a queen gets older. Therefore, Treanore examined whether nutrient storage and oxidative stress change over the life course of a queen prior to entering diapause.

The results of Treanore's research, reported in Conservation Physiology, indicate that heavier queens survive longer diapause periods, and her research suggested there is an ideal age for queens to enter diapause. Bees in habitats with low-floral availability may face tradeoffs between acquiring sufficient nutrients and time spent foraging in the field prior to entering diapause. Delaying diapause may allow for sequestering more nutrients but also may result in the accumulation of age-related stress. Conversely if a queen enters diapause without adequate nutrient reserves, she may not be able to cope with the energetic demands required of months in diapause.

The findings of this study emphasize the imperative for queens to accumulate nutrients prior to entering diapause within a narrow time window. A mismatch between the availability of high-quality resources may lead to queens accumulating nutrition over a longer period, resulting in increased oxidative stress and entering diapause in a suboptimal condition. Bumble bee declines have previously been linked to reduced floral resource availability, and this study further highlights the importance of providing bees with adequate access to floral resources throughout the summer and into the fall.