Abstract
The desert locust, a form of grasshopper, is a notorious plague insect. Swarms of locusts can extend over several hundred square kilometers with up to 80 million individuals per km2, posing severe threats to global food security. However, locusts do not always swarm. When food is abundant and population density is low, individuals remain as cryptic and sedentary ‘solitarious’ grasshoppers. Population upsurges and swarming arises when food scarcity in highly populated areas forces locusts to aggregate around limited resources, causing a transition to the ‘gregarious’ swarm-forming phase. Although behavioral and physiological changes associated with crowding have been widely documented, the biological mechanisms mediating the initiation of swarming and collective migrations are not well understood. We combine laboratory swarming assays with virtual reality and RNA sequencing to investigate when and how collective locust marching emerges. We use motion capture technology to continuously monitor the behaviour of solitary locusts during their first exposure to marching bands of gregarious conspecifics across several days. Preliminary findings suggest that, while rapid changes in response to conspecifics can be observed within a few hours, these do not appear sufficient to drive persistent phenotypic changes. Instead, solitary locusts displayed instances of marching-like behaviour after one day of crowding and started continuously marching only after multiple days of exposure to conspecifics. Complementary experiments in virtual reality - where individual locusts are embedded within immersive, responsive, and photorealistic virtual swarms with predefined statistics – demonstrate that exposure to moving virtual conspecifics is sufficient to trigger marching behaviour in solitary locusts crowded for three days. Further analyses will provide deeper insights into how changes in individual interaction maps and kinematics can lead to the formation of coordinated marching events.
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