Abstract
Pathogens may gain a fitness advantage through manipulation of the behaviour of their hosts. Likewise, host behavioural changes can be a defence mechanism, counteracting the impact of pathogens on host fitness. We apply harmonic radar technology to characterize the impact of an emerging pathogen - Nosema ceranae (Microsporidia) - on honeybee (Apis mellifera) flight and orientation performance in the field. Honeybees are the most important commercial pollinators. Emerging diseases have been proposed to play a prominent role in colony decline, partly through sub-lethal behavioural manipulation of their hosts. We found that homing success was significantly reduced in diseased (65.8%) versus healthy foragers (92.5%). Although lost bees had significantly reduced continuous flight times and prolonged resting times, other flight characteristics and navigational abilities showed no significant difference between infected and non-infected bees. Our results suggest that infected bees express normal flight characteristics but are constrained in their homing ability, potentially compromising the colony by reducing its resource inputs, but also counteracting the intra-colony spread of infection. We provide the first high-resolution analysis of sub-lethal effects of an emerging disease on insect flight behaviour. The potential causes and the implications for both host and parasite are discussed.
Highlights
Behavioural changes in the host in response to infection, whether as a side-effect of infection or an active manipulation by the pathogen or a behavioural response of the host, can have profound direct and indirect effects on both parasite and host [1]
Experimental Bees Over the course of the experiment we introduced a total of 2030 bees to the host colony (HC), of which 713 were inoculated with N. ceranae (Nc)
As bees of all three treatment groups originated from a common brood-frame and developed within the same colony environment, the age groups of these bees was assumed to be similar across treatments
Summary
Behavioural changes in the host in response to infection, whether as a side-effect of infection or an active manipulation by the pathogen or a behavioural response of the host, can have profound direct and indirect effects on both parasite and host [1]. Such behavioural effects may actively facilitate the transmission of the pathogen, such as by active exposure to susceptible hosts or navigational deficits leading to higher encounter rates with new prospective hosts Social insects are a prime model to study the behavioural effects of pathogens and their consequences, emphasised by the enormous economic and ecological roles some of these species have as pests (e.g. ant species, termites) and as pollinators (e.g. bees)
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