Comparison of Water Relation in Two Powderpost Beetles Relative to Body Size and Ontogenetic and Behavioral Traits.

Abstract

Heterobostrychus aequalis (Waterhouse) (Coleoptera: Bostrychidae) and Lyctus africanus Lesne (Coleoptera: Lyctidae) are distributed mainly in tropical regions. The primary mechanism allowing these beetles to survive in cold and arid habitats beyond the native tropical region is a reduced water loss rate. This study investigated the water relations of these two beetles in relation to their size, ontogenetic traits, and behavioral characteristics to determine how they can survive in desiccated wood. H. aequalis and L. africanus share similar water characteristic with beetles living in desert and woodlands. They have high percentage total body water (%TBW) content (58.38 ± 1.86% to 63.20 ± 1.38%), but low %TBW loss (4.28 ± 1.02% to 48.26 ± 8.28%) due to their impermeable cuticle (cuticular permeability [CP] value: 0-15.57 ± 4.90 µg cm-2 h-1 mmHg-1) at all life stages. Although the larvae of L. africanus exhibited relatively high %TBW loss, they had relatively shorter development times that minimized prolonged exposure to dry conditions inside the wood. The aggregative behavior of the adult could be responsible for maintaining a low water loss rate to compensate for their small body size. In contrast, the larvae of H. aequalis had larger body size and significantly lower CP values, allowing them to survive in the desiccated wood for a longer period of time. These results demonstrate the remarkably sophisticated strategies that insects employ as a trade-off between body size, ontogenetic development, and insect sociality (aggregative and non-aggregative behavior) to maintain their water balance in xeric environments.