Olfactory Strategies in the Defensive Behaviour of Insects

SIMPLE SUMMARY: Insects have several methods to protect themselves and their resources from danger. One of them is to use their sense of smell. In this review, we describe how insects use smell to detect threats and perform behaviours of ‘flight or fight’ such as avoidance, escape or attack, in order to protect themselves. We also discuss how group-living insects share the information of danger through semiochemicals called alarm pheromones, to act as a collective. In the second section of this paper, we review how these odours are processed in insect brains. We discuss how the two kinds of neural architectures observed in olfactory areas, labelled-lines and across-fiber patterns, support the processing of alarm pheromones. Finally, we give an outlook on potential future studies that will help us understand this field better. ABSTRACT: Most animals must defend themselves in order to survive. Defensive behaviour includes detecting predators or intruders, avoiding them by staying low-key or escaping or deterring them away by means of aggressive behaviour, i.e., attacking them. Responses vary across insect species, ranging from individual responses to coordinated group attacks in group-living species. Among different modalities of sensory perception, insects predominantly use the sense of smell to detect predators, intruders, and other threats. Furthermore, social insects, such as honeybees and ants, communicate about danger by means of alarm pheromones. In this review, we focus on how olfaction is put to use by insects in defensive behaviour. We review the knowledge of how chemical signals such as the alarm pheromone are processed in the insect brain. We further discuss future studies for understanding defensive behaviour and the role of olfaction.