Onset of morning activity in bumblebee foragers under natural low light conditions. Issue 11 (1st May 2021)

• Record Type: Journal Article
• Authors: Hall, Katie; Robert, Théo; Gaston, Kevin J.; Hempel de Ibarra, Natalie
• Is Part Of: Ecology and evolution. Volume 11:Issue 11(2021)
• Page Start: 6536
• Page End: 6545
• Publication Date: 2021-05-01
• Subjects: bees -- experience -- foraging -- learning -- navigation -- vision; Ecology -- Periodicals; Evolution -- Periodicals; 577.05
• DOI: 10.1002/ece3.7506
• Languages: English
• ISSNs: 2045-7758

Abstract

Abstract: Foraging on flowers in low light at dusk and dawn comes at an additional cost for insect pollinators with diurnal vision. Nevertheless, some species are known to be frequently active at these times. To explore how early and under which light levels colonies of bumblebees, Bombus terrestris, initiate their foraging activity, we tracked foragers of different body sizes using RFID over 5 consecutive days during warm periods of the flowering season. Bees that left the colony at lower light levels and earlier in the day were larger in size. This result extends the evidence for alloethism in bumblebees and shows that foragers differ in their task specialization depending on body size. By leaving the colony earlier to find and exploit flowers in low light, larger‐sized foragers are aided by their more sensitive eyes and can effectively increase their contributions to the colony's food influx. The decision to leave the colony early seems to be further facilitated by knowledge about profitable food resources in specific locations. We observed that experience accrued over many foraging flights determined whether a bee started foraging under lower light levels and earlier in the morning. Larger‐sized bees were not more experienced than smaller‐sized bees, confirming earlier observations of wide size ranges among active foragers. Overall, we found that most foragers left at higher light levels when they could see well and fly faster. Nevertheless, a small proportion of foragers left the colony shortly after the onset of dawn when light levels were below 10 lux. Our observations suggest that bumblebee colonies have the potential to balance the benefits of deploying large‐sized or experienced foragers during dawn against the risks and costs of foraging under low light by regulating the onset of their activity at different stages of the colony's life cycle and in changing environmental conditions. Abstract : It is widely believed but little evidenced that some diurnal pollinators, such as bumblebees, start foraging very early on flowers to avoid competition. Recording with RFID, we find that despite their high visual sensitivity very few foragers leave at the earliest opportunity in very low light in the mornings of warm days in spring and summer. We further show evidence for alloethism, but extend it by finding evidence for foraging specialisation in larger bees and a role of experience. Both factors enable the colony to adaptively deploy foragers in the early morning when the environment changes or their needs in different stages of the colony's life cycle.