Effects of three host pine species on diapause induction and life-history traits of Monochamus alternatus alternatus (Coleoptera: Cerambycidae).
Monochamus alternatus alternatus Hope is distributed in China and Taiwan and transmits the pinewood nematode, the causative agent of pine wilt disease. Unlike univoltine and semivoltine Monochamus alternatus endai Makihara native to Japan, M. a. alternatus has two generations a year (bivoltinism). Some polyphagous insect herbivores exhibit that the incidence of diapause is affected by the host plant species on which they feed, resulting in a host plant dependent variation in the number of generations a year (voltinism). For evaluating the effects of alien pine species on the colonization of M. a. alternatus, its larvae were reared on bolts of Pinus densiflora and P. thunbergii native to Japan and P. echinata native to North America in the laboratory. This study indicated that the three pine species did not increase the incidence of larval diapause to 1.0, suggesting that any pine species did not change the voltinsim. It also determined that the pine species did not influence the ovariole number of females that forwent diapause. The impact of feeding on P. densiflora and P. thunbergii on adult body mass was variable and there was no difference in adult body mass between P. densiflora and P. echinata. Thus, this study suggested that the voltinism of M. a. alternatus was not altered by some pine species native to unoccupied regions such as Japan and North America, i.e. its reproductive rate per year did not decrease owing to reduced number of generations per year, when it arrived there and then colonized.