Behavioral and physiological insights into cross-stage interactions in the desert locust

Gregarious desert locusts produce stage-specific pheromones that facilitate cohesive behavior in juveniles and synchronize maturation and mating in sexually mature adults. During locust outbreaks, merging populations result in cross-stage interactions, yet their impact on locust biology remains poorly understood. This study tested the hypothesis that cross-stage interactions influence juvenile cohesion and physiological traits. Using behavioral assays and gas chromatography-mass spectrometry, we examined short- and long-term interactions between juvenile and adult desert locusts. In short-term (24 h) cage assays, the presence of adults did not significantly affect grouping behavior in gregarious 3rd instar nymphs, as measured by the mean distance between individuals. Likewise, overall, juvenile pheromone emissions, based on previously identified nymphal components, showed no significant differences regardless of adult presence. Cross-stage interactions also had no measurable effect on the development time of 3rd instar nymphs. In contrast, long-term assays showed that 1st instar nymphs grouped with adults matured faster and grew heavier than older nymphal instars and fledglings, and, as mature males, released higher levels of phenylacetonitrile (PAN). Additionally, adult females emerging from these interactions oviposited earlier and laid more eggs than those not exposed to adults as juveniles. These findings indicate that cross-stage interactions impact development uniquely across different gregarious locust stages. Additionally, they offer important insights into desert locust behavior and chemical ecology, which could aid in developing more effective management strategies.