Abstract
Social insects have high levels of cooperation and division of labor. In bumble bees this is partly size-based, with larger bees performing tasks outside the nest and smaller bees remaining inside, although bumble bees still display considerable behavioral plasticity. The level of specialization in tasks outside the colony, including foraging, guarding and drifting (entering a foreign colony), is currently unknown for bumble bees. This study aimed to assess division of labor between outside tasks and the degree of specialization in foraging, guarding, and switching colonies in commercially reared bumble bees placed in the field. Nine factory-bought Bombus terrestris colonies were placed on three farms in Sussex, UK, between June and August 2015. Forty workers from each colony were radio-tagged and a reader on the colony entrance recorded the date, time and bee ID as they passed. The length and frequency of foraging trips and guarding behavior were calculated, and drifting recorded. The mean (±SD) length of foraging trips was 45 ± 36 min, and the mean number of foraging trips per day was 7.75 ± 7.71. Low levels of specialization in guarding or foraging behavior were found; however, some bees appeared to guard more frequently than others, and twenty bees were categorized as guards. Five bees appeared to exhibit repeated “stealing” behavior, which may have been a specialist task. The division of labor between tasks was not size-based. It is concluded that commercial bumble bees are flexible in performing outside nest tasks and may have diverse foraging strategies including intra-specific nest robbing.
Highlights
Social insect societies are characterized by a high level of cooperation, with workers forsaking their own reproduction for that of the queen, and division of labor, where different individuals take on different tasks (Westhus et al 2013)
The workers were placed into queen marking tubes in the lab and a radio-frequency identification (RFID) tag was attached to the thorax using glue
This study provides insight into the specialization and division of labor of behaviors performed by commercial bumble bees outside of the nest: foraging, guarding and drifting, including stealing and switching colonies
Summary
Social insect societies are characterized by a high level of cooperation, with workers forsaking their own reproduction for that of the queen, and division of labor, where different individuals take on different tasks (Westhus et al 2013). There is some age-based division of labor in bumble bees, as recently emerged workers remain within the nest performing nursing tasks and will switch to foraging tasks later in their life (Cameron 1989; O’Donnell et al 2000; SilvaMatos and Garófalo 2000). There is some evidence that larger bees are more efficient foragers, a potential explanation for the size-based division of labor (Goulson et al 2002; Klein et al 2017; Spaethe and Weidenmüller 2002). This was only the case for nectar foraging, and not pollen collection (Goulson et al 2002; Spaethe and Weidenmüller 2002). Display considerable plasticity in their behavior (O’Donnell et al 2000)
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