Impacts of agrochemicals and bacterial supplementation on honeybee health and performance

<p dir="ltr">Honeybees are globally important pollinators which are often exposed to agrochemicals like the herbicide glyphosate and the antibiotic oxytetracycline (OTC). Research over the last decade has demonstrated that glyphosate and OTC adversely affect honeybee health, behaviours, and cognition, raising concerns for honeybee wellbeing. Despite this, it remains unclear how these effects translate to foraging performance in the field, how developmental exposure impacts adults, and the underlying mechanisms involved. One potential mechanism is that exposure to glyphosate and OTC disturbs the honeybee gut microbiome, which is linked to bee health, performance, and neurological functions. If these agrochemicals impact bees via the gut microbiome, supplementing honeybees with naive core gut bacteria to replenish depleted bacterial members and restore gut community function may mitigate the adverse impacts.</p><p dir="ltr">In this thesis, I reviewed the potential pathways in which gut bacteria may alter honeybee cognitive functions by influencing bee neurochemistry, gene expression, and metabolite profiles (chapter two). I examined the development of agrochemical effects and found that the duration from initial exposure to glyphosate and OTC plays a role in their impacts on honeybee learning and survival. This delay in effects may indicate the gut microbiome’s involvement in the underlying mechanism. I found tentative evidence that bacterial supplementation may alleviate these adverse impacts following agrochemical exposure (chapters three and four). I next examined the effects of adult and developmental exposure to these agrochemicals and bacterial supplementation under field conditions. Although adult exposure did not reduce survival or foraging performance, developmental exposure to glyphosate reduced worker foraging performance. Moreover, I observed queenlessness in glyphosate exposed colonies (chapters five and six).</p><p dir="ltr">These findings suggest glyphosate and OTC can harm honeybee colony health, functioning, and longevity. However, by identifying these impacts we can improve safe usage recommendations. Furthermore, understanding the mechanisms that drive these effects can help us avoid or mitigate them. Bacterial supplementation, carried out with ecological consideration, could support colony management and recovery strategies, and enhance honeybee welfare.</p>