Context-dependent coordination of movement in Tribolium castaneum larvae.

Insect pests such as the red flour beetle (Tribolium castaneum) destroy up to 20% of stored grain products worldwide, making them a significant threat to food security. Their success hinges upon adapting their movements to unpredictable, heterogeneous environments like flour. Tribolium is well developed as a genetic model system; however, little is known about its natural locomotion and how its nervous system coordinates adaptive movement. Here, we employed videographic whole-animal and leg tracking to assess how Tribolium larvae locomote over different substrates and analyse their gait kinematics across speeds. Unlike many hexapods, larvae employed a bilaterally symmetric, posterior-to-anterior wave gait during fast locomotion. At slower speeds, coordination within thoracic segments was disrupted, although intersegmental coordination remained intact. Moreover, larvae used terminal abdominal structures (pygopods) to support challenging movements, such as climbing overhangs. Pygopod placement coincided with leg swing initiation, suggesting a stabilising role as adaptive anchoring devices. Surgically lesioning the connective between thoracic and abdominal ganglia impaired pygopod engagement and led to escalating impairments in flat-terrain locomotion, climbing and tunnelling. These results suggest that effective movement in Tribolium larvae requires thoracic-abdominal coordination, and that larval gait and limb recruitment is context dependent. Our work provides the first kinematic analysis of Tribolium larval locomotion and gives insights into its neural control, creating a foundation for future motor control research in a genetically tractable beetle that jeopardises global food security.