Selective oviposition by adult females and larval growth of Dacne picta Crotch (Coleoptera

Dacne picta is one of the most important pests of cultivated shiitake mushrooms (Lentinula edodes) in Japan. To clarify the preferential oviposition of adults among different growing stages of mushrooms, survival and development of offspring, a census was taken in a cultivated field of the mushroom. Fruiting bodies of mushrooms were classified into three stages : growing, mature and decaying stages. A large number of adults and eggs were observed in and on the growing and mature stages of mushrooms, but few were observed on the decaying stage. Adult beetles, thus, disappeared from the mushrooms when they started to decay. An inoculation experiment of adult beetles on mushrooms revealed that the mortality of first stadium larvae was much higher in the decaying stage of the mushrooms. Rearing experiments on powdered mushrooms suggested that chemical inhibitors and/or nutritional deficiency was an important cause for the higher mortalities of the 1st stadium larvae. However, the hardening of decaying mushrooms may have prevented hatched larvae from actually consuming them. Thus, the mushroom stage chosen by ovipositing adults is closely related to the mortality of hatched larvae.