The smell of infection: Detecting infectious disease and determining mechanisms underlying the spread of disease in social insects

Asiri, Ayman 2025. The smell of infection: Detecting infectious disease and determining mechanisms underlying the spread of disease in social insects. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Infection poses a universal challenge for animals, and many species rely on behavioural and chemical cues to limit pathogen transmission. Social immunity mitigates this risk, yet the chemical cues driving responses remain poorly understood. This thesis explores whether there is a consistent “smell of infection” in honey bees and whether such cues regulate social immunity. Chapter 2 reviews volatile organic compounds (VOCs) associated with infection in insects, highlighting their potential for non-invasive disease surveillance. A comprehensive meta-analysis of all current studies sampling VOCs from honey bee infections (n=23) showed that infected and uninfected brood can be distinguished across major pathogens, including Varroa destructor, Paenibacillus larvae, and Ascosphaera apis (Chapter 3). Infection signatures were defined not by single biomarkers but by bouquets of volatiles. However, no studies focused on adult bees; an obvious gap given transmission occurs mostly between adults. This knowledge gap was addressed by sampling adult bees infected with Vairimorpha ceranae (Chapter 4), finding that volatile profiles shifted in detectable but transient ways. Discrimination was strongest at six and twelve days post-infection, driven by subsets of compounds whose abundances oscillated with infection stage, confirming that adult infections also alter VOCs. Whether olfactory cues mediate adult social immunity was then investigated (Chapter 5). Dyadic assays isolating volatile from low-volatility compounds showed no behavioural responses to infected bees, suggesting group context is critical. Field assays using observation hives confirmed this (Chapter 6): both infected and uninfected bees perfumed with infection scent were treated similarly when introduced into a colony; receiving heightened aggression, avoidance, and intensive grooming. This demonstrates that odour alone can trigger adult-focused social immunity, but only within the colony context. These findings show that infection alters volatile emissions across life stages and that olfactory cues mediate colony-level responses, with implications for social immunity, pollinator health, and non-invasive disease surveillance.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Biosciences
Subjects:	Q Science > Q Science (General)
Date of First Compliant Deposit:	18 November 2025
Last Modified:	18 Nov 2025 10:54
URI:	https://orca.cardiff.ac.uk/id/eprint/182480

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