NOTES ON THE BIOLOGY AND MORPHOLOGY OF FALSE CLICK-BEETLE LARVAE (COLEOPTERA:EUCNEMIDAE) JYRKI MUONA AND MARIANNA TERA ¨ VA ¨ INEN Finnish Museum of Natural History FIN 00014 - University of Helsinki Helsinki, FINLAND jyrki.muona@helsinki.fi Abstract The function of microtrichial patches and areoles found in most eucnemid larvae is discussed. The areoles are regarded to be water excreting organs important for larval water- balance. The microtrichial patches were known to be an essential part of the larval locomotory method. It is suggested the modified spiracular collars associated with larvae of certain Dirhagini and Macraulacinae play a similar role. This appears especially clear with respect to Asiocnemis spp. The overall similarity between soft-bodied larvae of the few true wood-boring Eucnemidae is considered a homoplastic adaptation to multiple secondary invasions into relatively hard wood. Among beetle larvae, the early stages of most eucnemids are very unusual. They appear legless, have close to immobile, seemingly outward biting mandibles and leave next to no galleries in the soft rotten wood they develop in. A striking feature of these larvae is the presence of two types of plate-like structures on most segments of the body: the microtrichial patches and the areoles. Microtrichial patches. How eucnemid larvae penetrate their substrate remained a mystery for a long time (Lucht 1981). The key feature is a well-known structure of unknown function, the dull median patches on thoracic and abdominal segments. Most eucnemid larvae have them, often dorsally and ventrally. These patches have a silky shine and when studied under high magnification, they are covered with tiny groups of 2 to 4 spinulets. These patches have been known as ‘‘brosses de spinules’’ (Perris 1870), ‘‘matte patch’’ (Gardner 1935), ‘‘Samtplatte’’ (Leiler 1976), ‘‘Zahnpolster’’ (Lucht 1981), ‘‘velvety patch’’ (Burakowski 1989) or ‘‘microtrichial patches’’ (Lawrence et al. 2007). Lucht (1981) observed the larva of Hylis olexai Palm penetrating brown-rot wood with the help of fluid pressure, the lancet-shaped head and the microtrichial patches. With the onset of forward movement, the ninth abdominal segment was pumped nearly empty and partly withdrawn into the eighth. Simultaneously the metathorax was filled up and became swollen. Next, fluid from the metathorax was pumped into the mesothorax, and the metathorax in turn contracted dorsoventrally. Finally, fluid pressure was applied to the head. All the cephalic sclerites being entirely fused, the head did not swell, but instead was pressed forward through the wood. If the chisel-shaped head did not succeed in penetrating between the wood fibers, the larva moved its head along the horizontal axis and tried to break way in this fashion. The function of the microtrichial patches was to serve as secure attachment points against the wood for the swollen segments when the thrust was directed forward. The microtrichial patches vary in form and organization from species to species (Figs. 1–3). There is also variation during the development within one species — especially in hypermetamorphic larval types. Burakowski (1989) reported that The Coleopterists Bulletin, 62(4):475–479. 2008. 475