Behaviour of Foraging Bumble Bees Across Morphological and Environmental Contexts
Bumble bees as pollinators are being produced at an industrial scale and are used throughout the world to pollinate agricultural crops in glasshouses. The agricultural crops they are exposed to are often monocultural and mass-produced. The lack of floral variety they are provided with is thought to have negative effects on pollination performance and bee health, and has been suggested to influence worker drift in a glasshouse. Bumble bees are unique due to the large size differentiation among workers within a colony, which are thought to lead to consistent differences among individuals. Larger workers are more likely to be foragers, and smaller workers are more likely to perform in-nest tasks. These size differences are thought to cause differences among workers in foraging efficiency, the types of flowers they visit, and the size of their foraging ranges. Worker size also affects circadian rhythm strength, and individuals with stronger circadian rhythms are thought to anticipate potential activity cues such as sunrise. Bumble bees also show communication among foragers, but it is unknown whether they have ‘scouting’ bees that recruit inactive bees early in the day to forage. Understanding more about the behaviour of these populations and the effect environments can have on their activity is important for understanding how to aid in the conservation of these populations.Chapter 3 investigates bumble bee foragers and their activity among individuals of different sizes and within different colonies. I hypothesized (1) if bumble bees differ intrinsically from one another, then consistent differences in behaviour will be observed among foragers from the same colony and (2) if body size causes differences in anticipation of sunrise and foraging activity, then larger foragers will be seen initiating foraging earlier. To answer these questions, the nest entrance of two colonies were recorded that had access to a semi-natural floral environment in a glasshouse with tomato, cornflower and snapdragon flowers. Each bumble bee was marked with a coloured number tag to allow identification of each forager. Individuals differed from one another in foraging activity within both colonies. Additionally, larger workers initiated foraging earlier than smaller ones. The results support previous studies that show that individuals within a nest vary intrinsically from one another in foraging behaviour and show consistent differences within the same colony, as well as from other colonies. Moreover, larger bees appear to anticipate sunrise and potential food availability, suggesting the presence of strong diurnal foraging circadian rhythms, with larger bees leaving the next for the first time earlier than smaller bees. These differences among individuals could facilitate the temporal division of workers, and morphological differences could account for some of the variation seen among colonies.In chapter 4 I assessed bumble bee foraging activity across two different environments, a simple monofloral glasshouse, and an enriched polyfloral glasshouse. I hypothesised that (1) if simplified monocultures have a detrimental effect on bumble bee colonies, then decreased foraging activity will be observed in the simple environment compared to the enriched and (2) if nest switching behaviour is influenced by the availability of natural nectar sources, then lower levels of nest switching will be observed in the enriched environment. The methods of this chapter were the same as chapter 3, except that there were two glasshouses and four colonies. One glasshouse had 3 flower types including tomatoes, and the other only had tomatoes and artificial sugar syrup as a nectar source. I found that in the simple environment, bumble bees showed significantly decreased foraging activity, initiated foraging later, and spent less time out of the nest. Nest switching occurred at high rates and there was no difference among colonies or environments. These results show that bumble bee performance is affected by a monocultural glasshouse environment, and that nest switching occurs within a glasshouse independent of the environment they are exposed to.The research done in this thesis contributes to understanding bumble bee size differentiation and suggests that it may persist to separate workers temporally in activity. It shows differences among bumble bee foragers, and these foragers may differ from one another intrinsically or in thresholds to foraging tasks. It also provides insights into how monocultures and glasshouses can be affecting bumble bee colonies. This adds to literature about how monocultures may be having detrimental effects on pollinator species and reiterates the importance of providing a variety of floral resources to bees to enhance these populations.
Advisor: Jandt, Jennifer; Paulin, Michael
Degree Name: Master of Science
Degree Discipline: Zoology
Publisher: University of Otago
Keywords: Bumble Bees; Foraging; Behaviour; Body Size; Environmental Effects; Nest Drift; Bombus terrestris; Agricultural Intensification; Circadian Rhythms
Research Type: Thesis