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 at three sites and over five time periods during the 2016 flowering season in south-central Wisconsin. Pollen pellets 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 of season (period) and site, and their interactions, on multiple foraging effort metrics and on pollen dry weight. Relative to honey bees, individual bumble bees made more foraging trips each day, resulting in a greater time spent foraging. A greater proportion of RFID tagged bumble bees foraged each day and 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 the different foraging strategies of the two bee species, temporal and spatial variation in resource availability, and with reference to future research using miniaturized animal tracking technologies in the context of optimal foraging theory.
Highlights
87% of flowering plants around the globe (Ollerton et al, 2011) and 35% of all crops grown for human consumption (Klein et al, 2007) benefit from animal pollination
It varied between bee species, the proportion of tagged bees was not influenced by site or period or by any of the twoway interactions between bee species, site or period, or (Table 4)
The proportion of bees foraging each day was similar among sites and time of year and the pattern among sites or among periods was similar for the two bee species (Table 4)
Summary
87% of flowering plants around the globe (Ollerton et al, 2011) and 35% of all crops grown for human consumption (Klein et al, 2007) benefit from animal pollination. Exposure to neonicotinoid pesticides negatively affects the ability of honey bees to navigate back to their hive following artificial displacement (Fischer et al, 2014) and increases the foraging effort of bumble bees (Stanley et al, 2016). These sublethal effects of neonicotinoid pesticide exposure can further exacerbate the negative impacts of pathogens such as Nosema and black queen cell virus on bees (Doublet et al, 2015). Given the numerous challenges facing bees, a better understanding of bee foraging over time and space, and for distinct species would facilitate the development of sound conservation strategies
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