Relationship between walking activity and flight activity in the red flour beetle, <i>Tribolium castaneum</i>

Terrestrial animal species often employ both walking and flying as modes of locomotion. Although flight facilitates more efficient long-distance travel compared to ambulation, it imposes more stringent constraints on body mass. Consequently, birds frequently demonstrate an interspecific trade-off between their flight and walking capabilities. Despite this, the relationship between these two modes of transportation has not been explored in insects, which represent the Earth's most speciose group and possess both flight and walking abilities. This study investigated the relationship between walking and flight activities in the red flour beetle (Tribolium castaneum), a facultatively flying and walking insect. We utilized previously established strains selected for either high (H) or low (L) walking activity. We then compared flight activity and lipid content, which functions as metabolic fuel for flight, between the H and L strains. Our findings indicate that H-beetles exhibited significantly greater flight activity than L-beetles, demonstrating a positive correlation between walking and flying activity in T. castaneum. This suggests that, contrary to observations in birds, small insects such as T. castaneum do not incur a trade-off between walking and flight. Furthermore, L-beetles exhibited significantly higher proportion of body lipid mass, suggesting that individuals with reduced locomotor activity tend to accumulate more fat, irrespective of their primary mode of movement.