Spatial Distribution of Pine Bark Weevils (Coleoptera : Curculionidae) in Bait Logs

Abstract

The changes in spatial distribution pattern throughout the developmental period of three species of pine bark weevils, Shirahoshizo spp. (including S. rufescens, S. insidiosus and S. pini), Pissodes nitidus and Pissodes obscurus were observed.There were some differences among the species as for the spatial distribution of oviposition sites, that is, random distribution of P. obscurus, contagious distribution of P. nitidus and uniform distribution of Shirahoshizo spp. But, in all cases, most of the eggs were laid in masses and the distribution of young larvae at their peak was aggregative or colonial, originating in the mass oviposition, regardless of the difference of the spatial distribution of oviposition sites. While the population grew up and larvae dispersed from their hatched sites, the tendency for larvae of all the three species to disperse into random or regular distribution was consistently observed. But after the operation of main mortality factors on each population, the degree of aggregation was increased. The final distribution of pupal chambers of Shirahoshizo spp. was uniform and, on the other hand, these of P. nitidus and P. obscurus were contagious or random.