Neural control of movement in Tribolium castaneum larvae

Flour beetles such as Tribolium castaneum are devastating pests of dry stored grain products, causing up to 19% loss of these commodities in the Global South. Little is known about how the nervous systems of these animals coordinate effective movement. We therefore employed novel behavioural assays combined with whole-animal and leg tracking to assess how larvae move over different types of terrain. We found that larvae move most efficiently over fibrous substrates (e.g. paper), consistent with the beetle’s original habitat of tree bark. Locomotion over flat terrain primarily involves movements of their legs, while climbing extreme inclines involves both use of legs and repetitive planting of terminal abdominal segments. In contrast to many hexapods, leg movements are bilaterally symmetric during fast locomotion, with swing and stance phases propagating from posterior to anterior segments. During slow locomotion however, thoracic intra-segmental coordination is disrupted, while intersegmental coordination is largely preserved. Surgically severing the connective between thoracic and abdominal ganglia led to deficits in locomotion over flat terrain, deficits in climbing inclines, and impaired burrowing through flour. These results suggest that coordination of thoracic and abdominal segments is required for effective movement over and through substrates. Our work provides the first kinematic analysis of locomotion in Tribolium castaneum and first insights into the neural control of movement in this species. This work creates a foundation for future studies of motor control in a genetically tractable insect that directly impacts global food security.