Abstract
The population densities of three species of pine bark weevils, Shirahoshizo spp. (including S. rufescens ROELOFS, S. insidiosus ROELOFS and S. pini MORIMOTO), Pissodes nitidus ROELOFS and P. obscurus ROELOFS, living within bait logs (70-80-cm long, 15-20 cm in diameter) of Pinus densiflora SIEB. et ZUCC., were estimated in a pine forset. In all species, the larval density reached maximum at about forty days after the beginning of the attack by adults, thereafter the densities decreased throughout the larval stage. The initial larval density of Shirahoshizo spp. was the highest of all but it decreased rapidly after the peak. While the changes in larval density of P. nitidus and P. obscurus did not show such a great decrease and the pupal density of these species was higher than that of Shirahoshizo spp. A large number of larvae disappeared during their growth period, which accounted for 93.69, 80.75 and 52.00 percent of the total mortality of Shirahoshizo spp., P. nitidus and P. obscurus respectively. Parasitism was a severe factor operating on the old larval stage of Shirahoshizo spp. and P. nitidus, while larvae of P. obscurus seldom suffered parasitism.
