Survival and Mortality of Immature Mordellids (Coleoptera: Mordellidae) Inducing Stem-galls on the Japanese Mugwort

Abstract

Mordellid galls were collected from stems of Japanese mugwort, Artemisia indica var. maximowiczii (Nakai) H. Hara, in early spring at three riverbeds in the Kinki district, central Japan, and reared in the laboratory. Adults of two mordellids, Mordellistena brevilineata Nomura (96.2% of the total number of individuals) and M. fuscosuturalis Nomura (3.8%), emerged from the galls. The galls were simple fusiform swellings in the stems. We could not distinguish the 2 species by gall morphology. Mortality of the immatures mostly could not be determined, but parasitoids (Eupelmus sp., Entedon sp., and braconids, etc.) accounted for about 25% of the total mortality observed. Survival of immatures tended to be higher and the concomitant parasitism lower in thicker rather than thinner galls, and the galls became thick when they were formed in larger diameter stems. Oviposition and larval establishment in thick stems appeared to be advantageous for the completion of development and avoidance of parasitoid attack.