The effects of life history traits on the foraging ecology of bufftailed bumblebees (Bombus terrestris L.)

Abstract

Bumblebees are essential pollinators, sustaining ecosystem balance and aiding crop pollination. A comprehensive understanding of their foraging ecology is therefore crucial. We studied the influence of life-history traits of individual Bombus terrestris on wing wear and its foraging patterns. Wing wear is clearly a widespread phenomenon observed in all flying insects. Wing integrity has consequences for bumblebees on both the individual level, affecting the bee’s flight performance and life expectancy, and on the colony level, impacting the productivity and overall health of the hive. We investigated how the influence of individual intrinsic aspects, such as age, body size, and foraging activity, affects wing wear in B. terrestris. We also observed the different aspects affecting the behaviour of bumblebees, causing different foraging effort and influencing pollen collection. Our findings revealed a multifactorial explanation for the loss of wing integrity in B. terrestris. Wing wear was associated with increasing age and larger body size. More wing degradation was also observed as foraging activity intensified. Additionally, we found foraging effort to be influenced by both age and body size, with a higher foraging intensity and a higher efficiency in pollen collection for older and larger individuals. Exploring how foraging patterns are shaped by individual characteristics is essential for understanding pollination and colony development. Future studies are needed to better understand the age and intrinsic structure of bumblebees in relation to their individual and collective production.

Popular Abstract

The effects of life history traits on the foraging ecology of buff-tailed bumblebees (Bombus terrestris L.)

Insect pollinators are of vital importance for maintaining ecosystems functioning and are essential to agricultural productivity. Global biodiversity declines as well as changes in climate and habitats impact essential pollinators like bumblebees, which play an important role in both crop and wild plant pollination. Bumblebees (family Apidae, genus Bombus) are widespread and generalist foragers, making them particularly important pollinators in wild and managed ecosystems. Understanding the foraging patterns and habits of bumblebees is vital due to this essential role.

Intrinsic factors such as age and body size significantly influence individual foraging behaviour and flower preference. Different foraging habits may lead to consequences such as higher mortality rates and increased wing wear. Wing wear, described as the loss of wing integrity, is a widespread phenomenon observed in all flying insects. Bumblebees depend heavily on their wings, as they are essential for foraging pollen and nectar for plants, to feed the larvae and to sustain the colony. Wings of bumblebees have been observed to become increasingly damaged as individuals age. Consequently, attempts have been made to try and associate a stage of wing degradation to a specific age of an individual. However, estimating age in wild bumblebees through wing wear is complex due to numerous damage factors, such as age, body size, foraging activity.

This project examined the different causes of individual changes in wing wear, foraging patterns and flower preference of buff-tailed bumblebees (Bombus terrestris).

Methods
During the summer of 2024, we studied 40 B. terrestris colonies around the Ecology building, Department of Biology, Lund University (55°42'51.0"N, 13°12'31.0"E). The hives were nested inside wooden boxes placed in four different sites, with four successive rounds of 10 hives set at 2-week intervals. Each studied bee was identifiable through a unique numbered tag placed on their thorax. By recording the newly emerged bees’ tag number and tagging date, we created a record of individuals’ age. The colonies’ activity was observed during several monitoring sessions each, during which we noted the tag number of the bees entering or exiting the hive. If a bee was observed carrying pollen, we collected it for taxonomic identification. The pollen grains were then scanned to identify the different pollen groups present in each collected sample. To study wing wear, we photographed the wings of the bees of known age over the course of three weeks and used computer-vision based thresholding techniques for segmentation and area calculation of the wing cells.

Wing wear
Our study revealed that several factors influence wing wear. Older and larger bees displayed greater loss of wing area, as for individuals with a high foraging rate. Predation, object collisions and decreased stability affected mortality rates due to increased wing degradation, lowering life expectancy for foragers. Increased mortality and changes in flight strategies of individuals due to a loss of wing integrity affects the colony as a whole. The number and efficiency of workers is reduced, diminishing colony performance. The results of our study suggest that we may not yet be able to fully achieve age prediction based on the degree of wing degradation, as age is not the only influencing factor on wing wear.

Foraging ecology and pollen collection
Our findings indicate that, as individual age, their foraging frequency and efficiency increase, allowing them to make more trips and collect heavier pollen loads. This trends continues until they reach a peak in carried pollen weights between 5 and 10 days of age, after which the weights gradually decline towards the end of the bumblebee’s life. Based on our results, larger bees appear to contribute substantially to the colony structure and productivity, having a higher foraging rate and bringing heavier pollen loads to the hive. Although larger bees are more active, their contribution to the colony diminishes towards the end of their life, which may not significantly benefit the colony overall, as they experience greater wing degradation over time.

Finally, we observed that older bees tended to return to the hive with more diverse pollen loads. Samples were dominated by one or two pollen types, with Tilia pollen being the most common. The relationship between age and flower preference can be understood through increased experience with time. Bumblebees modify their foraging patterns as they age and the variety of flowers foraged changes as an individual’s knowledge of the area widens. More experienced bumblebees tend to extensively visit highly rewarding flowers. Flower preference can also be explained through seasonal changes and flower availability. Understanding flower preference at the individual level is important to understand how individual bumblebee choices shape the entire colony’s development.

Conclusion & future studies
We observed that older and larger bees foraged more and, consequently, displayed more wing degradation. Age and body size also influenced the quantity and diversity of pollen carried by bumblebees, varying with time and body size. Further studies on these factors could lead to better age prediction methods based on wing wear. By evaluating the stage of wing degradation of a specific bumblebee, we could ascertain its age and, thereafter, its anticipated foraging activity and pollen collection abilities. By doing so, the expected collective foraging effort and pollen collection of a colony could be known, enhancing our understanding of the colony and individual-level processes that affect ecosystem functioning.


Master’s Degree Project in Biology, 60 credits, April 2025
Department of Biology, Lund University
Advisors: Charlie Nicholson and Ola Olsson

• author: Jodogne--Del Litto, Zélie
• supervisor: Charlie Nicholson; Ola Olsson
• organization: Degree Projects in Biology
• course: BION03 20241
• year: 2025
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 9188132
• date added to LUP: 2025-05-07 13:47:19
• date last changed: 2025-05-07 13:47:19