Seasonal abundance and oviposition preference of the alfalfa weevil Hypera postica on Vicia sativa subsp. nigra

The alfalfa weevil Hypera postica (Gyllenhal) is the most serious invasive pest of Chinese milk vetch, Astragalus sinicus L. H. postica also feeds on the leguminous plant Vicia sativa subsp. nigra (L.), an important host as a source of H. postica infections. We investigated the seasonal abundance and oviposition preference of H, postica on V. sativa subsp. nigra in Hisayama town, Fukuoka Prefecture, Japan. H. postica eggs were observed on V. sativa subsp. nigra throughout the study from January 11 to May 11, 2011 and the peak density of H, postica larvae was observed in April 11. Rapid growth of V. sativa subsp. nigra from March 27 to April 11 corresponded with the increasing population density of H. postica larvae. The numbers of H. postica eggs positively correlated with the diameter of V. satim subsp. nigra stems in the results of January 11 to April 11. We investigated the oviposition preference using field samples. To investigate oviposition preference behavior, an additional study should be performed in the laboratory.