Burrowing depth mediates the extent of metabolic suppression in a soil‐overwintering insect

Abstract

Abstract Conserving energy through winter is important for the fitness of temperate insects. While insects can use buffered microhabitats, metabolic suppression or decreases in the thermal sensitivity of metabolic rate to override seasonal‐scale thermal trends, the relative importance of these strategies for limiting energy use by insects overwintering in soil remains underexplored. We used a combined laboratory, field and simulation approach to investigate the overwintering energetics of the western bean cutworm (Striacosta albicosta), a univoltine lepidopteran pest of dry beans and corn that overwinters underground as a dormant prepupa. We hypothesised that (1) the selection of thermally buffered microhabitats (i.e. deeper soil sites) reduces energy use in early autumn and late spring, and that (2) changes in the metabolic rate–temperature relationship reduce the impact of elevated temperatures on overwintering energy use. We provide evidence that during the warmest parts of winter, dormant S. albicosta prepupae that had burrowed deep benefited from a cool, stable microclimate, whereas those near the soil surface appeared to rely on deeper metabolic suppression to maintain their energy stores. Although elevated temperatures in the laboratory depleted their energy reserves, these strategies appear sufficient to limit energy drain under natural conditions in the field. We suggest that small‐scale variation in the depth of soil refuges may mediate the interaction between the risk of energy drain and changes in the metabolic rate–temperature relationship in soil‐overwintering insects. Read the free Plain Language Summary for this article on the Journal blog.