Chemosensory mechanisms of starch detection and oviposition site selection in the powder-post beetle Lyctus brunneus (Stephens) (Coleoptera, Bostrichidae)

Abstract The powder-post beetle Lyctus brunneus (Stephens) causes a great deal of damage to dry hardwood and bamboo. Adult females oviposit only on wood or bamboo with a sufficient starch content. Although starch detection has traditionally been attributed to a behavior known as “tasting”, in which females gnaw the wood surface with their mandibles to make small incisions, recent observations suggest that this behavior may function primarily as a mechanical preparation for ovipositor insertion rather than as a true chemosensory action. Consequently, the mechanism by which L. brunneus females actually detect starch remains unclear. This study elucidated how L. brunneus detects the polysaccharide starch to select optimal oviposition sites, including the organs involved and the detection method. We examined the role of mouthparts (maxillary and labial palps), antennae, and tarsi in starch detection by evaluating egg-laying responses after functionally inhibiting these organs. Our investigations revealed that the coating of the mouthparts resulted in a significant reduction in the number of eggs laid, implicating the maxillary and labial palps' involvement in the detection of starch by L. brunneus . Scanning electron microscopy confirmed the presence of gustatory sensilla on the maxillary and labial palps. Testing the effects of several types of sugars on egg-laying numbers revealed that females laid significantly more eggs on starch and maltose than on glucose, sucrose, or control substrates. When female adults were placed on starch-containing substrates for designated periods, maltose was detected within the substrates. These results suggest that female adults secrete amylase externally to decompose starch, then detect the resulting maltose using gustatory sensilla on the maxillary and labial palps, to perceive starch sources—that is, optimal oviposition sites.