Rosalia batesi Harold (Cerambycidae: Cerambycinae: Rosaliini) is associated with dead wood of many hardwood species in Japan mainland. Larvae have been observed to bore into heartwood, the least nitrogen-rich biomass. Little is known about its precise bionomics, however. In the present study, its larval boring habit was investigated together with another polyphagous dead-wood-boring cerambycine, Chlorophorus quiquefasciatus (Laporte & Gory) (Clytini) for comparison. Observations were carried out using boles of Pasania edulis (Makino) Nakai (Fagaceae) as their boring substratum. Larvae were regularly sampled to record the body weight, frass weight, larval tunnel volume, and C and N contents of larval body, frass and wood. The observations and measurements revealed no significant differences in mid-instar larvae for boring position within the wood substratum, the total length of the larval tunnels, and some other ecological factors between R. batesi and C. quinquefasciatus. On the contrary, R. batesi mature larva alone exhibited quite a different result from the others in the total length of tunnels, frass quantity, boring position, etc., suggesting quite different boring strategies of R. batesi larvae when matured. Rosalia batesi larva thus is thought to have a strategy, while young, of boring cambial and sapwood regions of the bole, obtaining more nutritious wood tissues as food, setting more importance on food quality than quantity, and then to have a strategy, when grown-up, of boring inner portion including heartwood, obtaining less nutritious tissues, setting more importance on food quantity than quality, with the latter situation likely involving less conspecific and/or heterospecific competitions and less hazzard of natural enemies.
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