Impact of landscape on honey bee pollen diet, pesticide exposure and cognition

Abstract

The European honey, Apis Melifera L., is the most commonly managed bee in the world, but despite an increase in the global stocks of honey bees, areas such as Europe (-26.5%) and North America (-49.5%) have experienced notable declines at the colony level. Although less data is available on the position of honey bees in the tropics, what is available suggests that there is a deficit of 210,00 honey bee hives compared to global trends. These declines are driven by a number of synergistic stressors, including land use change, pesticide exposure, as well as pathogen and parasite infection. This thesis investigates how in a tropical environment, Belize, the Africanised honey bee is impacted by the landscape, and in particular their subsequent diet and exposure to pesticides. Apiculture is one of the most widespread agricultural activities practised globally, with an estimated 94 million honey bee colonies present worldwide in 2020. Beekeeping offers substantial benefits to local people, particularly in rural developing communities, where it provides economic opportunities, through the production of honey, wax and bee bread. In addition, the impact of landscape on honey bee learning in the UK was also analysed, and for the first time directly compares visual learning across a gradient of landscapes, contributing to the growing knowledge of bee behaviour and cognition. Analysis of the honey bee pollen diet across the Toledo and Cayo districts of Belize was carried out by identifying the pollen grains in bee bread samples. The most abundant and frequently occurring taxa were identified and community compositions studied. Tree species were found to be of particular importance, making up 80% of the 10 most relatively abundant species. This study contributes to the growing body of research highlighting the importance of trees in bee diets. No relationship was found between the most abundant pollen taxa and their nutritional make up based on crude protein levels, suggesting that the abundance of the pollen in the environment is more likely the driver behind its dominance in the bee bread. The effects of landscape diversity on species richness, species diversity and community compositions of pollen found in bee bread was compared in the Toledo and Cayo districts. A negative relationship was found between landscape diversity and both pollen richness and diversity. This may be due to the complex relationship between each plant/pollen taxa and the landscape, as well as bee preference. A high abundance of preferred species within the landscape acts to lower the diversity and richness of pollen with the honey bees diet. This data suggests that the presence and dominance of preferred species in the landscape is more important than landscape diversity when it comes to determining honey bee diet. The presence of pesticides in bee bread samples from honey bee hives located across a gradient off natural and agricultural landscapes was also investigated. Pesticides were not found in any of the samples, suggesting that exposure of honey bees to pesticides via their pollen diet does not represent a risk in Belize. The lack of pollen contamination of pesticides is likely due to the bees preference of tree pollen which does not receive pesticide treatment, and is unlikely to experience accidental treatment due to the main application methods in Belize, knapsack spraying. Finally, the effects of landscape complexity and composition on honey bee cognition was studied directly in the field. Visual learning, a crucial component of bee behaviour used to find food resources, was compared across a gradient of landscapes with a range of complexity, whilst compositional changes were kept to a minimum. To do this a field adapted version of the proboscis extension response was utilised, and bees were taught to associate different coloured paper strips with positive and negative rewards. Results showed that as landscape edge density increased bee learning reduced, and while landscape diversity increased so did bee learning. This is important as to ensure colony survival, bees must learn foraging routes, find profitable flowers, develop spatial maps as well as recognise intruders. Landscape has been shown to be an influential factor in both determining the pollen diet of bees as well as their learning ability, but in Belize did not contribute to pesticide exposure through their pollen diet, likely due to the pesticide application methods and bee preference for tree species. When placing bee hives in both Belize and the UK, it is therefore important to consider there placement in terms of landscape, to increase the likelihood of developing a strong and successful colony.

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Identifiers

ORCID for Suleiman Sharkh: orcid.org/0000-0001-7335-8503

ORCID for Jake Snaddon: orcid.org/0000-0003-3549-5472

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