REGULATION OF BUMBLE BEE (Bombus impatiens) WORKER REPRODUCTION BY BROOD
Open Access
- Author:
- Starkey, Jesse
- Graduate Program:
- Entomology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- July 14, 2019
- Committee Members:
- Etya Amsalem, Thesis Advisor/Co-Advisor
Christina M Grozinger, Committee Member
Thomas Charles Baker, Committee Member - Keywords:
- Bumblebee
Eusocial
Social Behavior
Reproductive division of labor
Brood
Worker reproduction
Bombus impatiens
Brood signal
Volatile pheromones
Pheromones
Choice bioassay - Abstract:
- Social insect species where egg laying is monopolized by a single or a few females have evolved multiple times in insects. These societies were always rooted in a simple family structure where adults care for the brood that is produce. Female reproduction in such families are often characterized by a tradeoff between reproduction and brood care. Yet, most work on the regulation of reproduction in social insects have focused on signals and traits exhibited by adults such as the queen or nestmate workers. Reproductive division of labor, whether it is controlled by the brood or adults, is often regulated by a combination of behavioral and chemical means. However, it is hypothesized that behavioral interactions play a more important role in regulating reproduction of primitive eusocial species, while pheromones are typically used by large size, advanced eusocial species. In this thesis, I examined the role of brood in regulating worker reproduction in Bombus impatiens, a primitively eusocial species where reproduction is dominated by the queen via an unknown mechanism. I further examined whether brood effect on worker reproduction is mediated via a pheromone produced by the offspring. I found that young larvae reduced worker egg laying, while the presence of pupae stimulated egg laying. These effects were quantity-dependent, with nearly complete suppression of egg laying in cages containing pair of workers and more than ten young larvae, and replicable regardless of worker age, relatedness to brood, or brood parentage/sex. I further showed that workers preferred pupae over larvae or control in a choice experiment, in line with their reproductive interests. However, odors from larvae or pupae were insufficient to inhibit worker reproduction. The youngest larvae were found to be particularly vulnerable to starvation, raising the hypothesis they produce a hunger signal. However, despite a slight attraction and fewer eggs laid by workers in the presence of starved vs. fed larvae, these effects were insignificant. The findings that any larvae can regulate worker reproduction in this simple eusocial species highlight the role of brood in the evolution of sociality and reproductive division of labor. Bumble bee workers may use a combination of cues or rely solely on behavioral interactions with brood and other females to make decisions about reproduction, in line with their small colony size and simple social organization. These findings also provide the first holistic explanation for the regulation of worker reproduction in B. impatiens, suggesting that ether the queen inhibits worker reproduction through her brood, or workers forgo their own reproduction based on honest signals of queen fertility given off by the brood.