Factors influencing walking speed in insects: not just a matter of size and age

Locomotion is essential but energetically costly for most animals. Walking has received substantial attention in insects, yet the impact of body size and age on walking speed within species has been the topic of relatively few studies. The first objective of this study was to survey the literature to test the hypothesis that, within insect species, walking speed is proportional to size and inversely proportional to age. The second objective was to investigate these relationships in egg parasitoid species that use walking speed to evaluate host quality and where an impact of size or age on walking speed would induce a bias in the perception of resource quality. As predicted, within an insect species, walking speed generally increases with body size and decreases with age, with some exceptions. Walking speed was size-dependent for Trichogramma pintoi and Trichogramma minutum, but was found to be both size- and age-independent for Trichogramma euproctidis. These results suggest that general patterns of walking speed observed in other taxa can be generalized for most insects. This relationship becomes less intuitive in species that use locomotion as a measuring tool (such as T. euproctidis), and may be selected to maintain walking speed constancy in the face of aging and phenotypic variation.