Strong interspecific differences in foraging activity observed between honey bees and bumble bees using miniaturized radio frequency identification (RFID)

Authors: MINAHAN, DANIEL - University Of Wisconsin; Brunet, Johanne

Submitted to: Frontiers in Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/18/2018
Publication Date: 10/5/2018
Citation: Minahan, D.F., Brunet, J. 2018. Strong interspecific differences in foraging activity observed between honey bees and bumble bees using miniaturized radio frequency identification (RFID). Frontiers in Ecology and Evolution. https://doi.org/10.3389/fevo.2018.00156.
DOI: https://doi.org/10.3389/fevo.2018.00156

Interpretive Summary: Bees are important visitors to both crops and wildflowers, yet many bee species are in decline as a result of habitat loss, pesticide exposure, and pathogens. Bees are central place foragers, implying that they must depart a nesting site, locate and gather resources, and return with these resources to the nesting area. Because the flowering plant species in a given habitat, and thus the identity, quantity and quality of resources vary through time and space, the strategies used by central place foragers to gather resources must be amenable to fluctuations in resource availability. Although honey bees and bumble bees are both eusocial central place foragers, they differ in many traits, including life history, colony size, within hive communication, body size and foraging strategies. While colonies of honey bees are perennial and very large (up to 60,000), bumble bees have significantly smaller (50-250) annual colonies. The dance language, an efficient mode of within-hive communication to share resource abundance and location to other foragers, is present in honey bees but absent in bumble bees. In the current study, we used miniaturized radio frequency identification (RFID) to track the foraging pattern of individual bees to and from the hive. We compared the European honey bee, Apis mellifera, and the common eastern bumble bee, Bombus impatiens. We also collected pollen sacs from bees returning to the hive. Linear mixed effects models determined whether foraging effort and pollen dry weight differed between the two bee species and whether they varied over the flowering season and among sites. Bumble bees put forth greater foraging effort relative to honey bees. Bumble bees allocated a greater proportion of their workforce to foraging each day and individual bumble bees did more foraging trips on a given day. Bumble bees also brought back heavier pollen sacs to the hive following a foraging trip compared to honey bees. Contrary to expectations, bumble bees spent the same amount of time foraging per trip as honey bees. In addition, none of the foraging effort metrics varied over the flowering season or among sites. Both bee species did, however, bring heavier pollen sacs back to the hive early and late in the flowering season relative to the three mid-periods. These results are discussed in terms of differences observed between these two bee species, temporal variation in colony need, and spatial and temporal variation in resource availability. Understanding how different bee species modulate effort to gather resources over space and time can help land managers improve conservation strategies for diverse pollinator communities. Given the significant bee decline observed in both agricultural and natural settings, the information gathered in this study will be useful to scientists and regulators, the general public and any organization interested in bee health and bee conservation.

Technical Abstract: Central place foragers depart from and return to a central location with enough resources for themselves, and in many cases, for the group. Honey bees and bumble bees are eusocial central place foragers. Honey bees use their unique dance language to recruit foragers to the most profitable patches. Bumble bees, on the other hand, exploit patches individually and develop trapline foraging patterns. Given the greater efficiency of the honey bee dance language for communicating the location of profitable resources to other foragers, based on optimal foraging theory, we predicted that bumble bees would put forth greater foraging effort than honey bees. We further hypothesized that both honey bees and bumble bees would respond to local resource availability, and that the foraging effort would reflect temporal fluctuations in colony needs. Using miniaturized radio frequency identification (RFID), we tracked the foraging patterns of individual bees to and from hives over the flowering season at three sites in south-central Wisconsin. Pollen sacs were also collected from bees returning to the hive. We compared the European honey bee, Apis mellifera, and the common eastern bumble bee, Bombus impatiens. Linear mixed effect models determined the impact of bee species, time period and site, and their interactions on multiple foraging effort metrics and on pollen dry weight. Individual bumble bees made more foraging trips per day, and a greater proportion of RFID tagged bumble bees foraged each day relative to honey bees. Additionally, bumble bees brought heavier pollen sacs to the hive compared to honey bees. Foraging bout duration did not vary between bee species and none of the foraging effort metrics varied among time periods or among sites. Both bee species, however, brought heavier pollen sacs back to the hive at the beginning and the end of the flowering season. These results are discussed in terms of differences between the two bee species, colony need, and temporal and spatial variation in resource availability, and with reference to future research using miniaturized animal tracking technologies.