We studied the host range of Asobara japonica, a larval-pupal parasitoid of drosophilid flies. Habitat selection was found to be an important determinant of host range in this parasitoid; it attacked drosophilid larvae breeding on banana and mushrooms, but seldom attacked those breeding on decayed leaves. This parasitoid was able to use diverse drosophilid taxa as hosts. Attack by A. japonica sometimes killed hosts at the larval stage, and therefore parasitoid larvae also died. Drosophila elegans and D. busckii suffered particularly high larval mortality due to the attack by A. japonica (in the latter species only when young larvae were attacked). Many individuals of D. subpulchrella also died at the pupal stage without producing parasitoids when they were parasitized at the late larval stage. In contrast, D. bipectinata, D. ficusphila, D. immigrans, D. formosana and D. albomicans were resistant to attack: large proportions of the larvae of these drosophilid species grew to adulthood, even in the presence of parasitoids. On the basis of phylogenetic information, we concluded that phylogenetic position has only limited importance as a factor determining whether a species is suitable as a host for A. japonica, at least within the genus Drosophila.

Ganaspis individuals parasitizing Drosophila suzukii (Matsumura), a pest of fruit crop, were examined for host use and molecular and morphological differences from those attacking D. lutescens Okada and some other Drosophila species that breed on fermenting fruits. Wild cherry fruits were collected in the suburbs of Tokyo, and drosophilid pupae obtained from these fruits were examined for parasitism.Drosophila suzukii was the only drosophilid species infesting fresh wild cherry fruits, and Ganaspis individuals were the major parasitoids attacking D. suzukii in wild cherry fruits. In parasitism experiments, these Ganaspis individuals parasitized D. suzukii larvae in fresh cherry fruits, but did not parasitize those in Drosophila medium. In addition, they did not parasitize larvae of some other fruit-feeding Drosophila species even when these occurred in fresh cherry fruit. These Ganaspis individuals parasitizing D. suzukii were different from those parasitizing D. lutescens and some other drosophilids in nucleotide sequences of the COI gene, as well as in ITS1 and ITS2.

Abstract. We studied variations in genetic, physiological, and ecological traits, and the phylogenetic relationship among sexual and parthenogenetic populations of Asobara japonica, a larval parasitoid of drosophilid flies, in order to understand how they adapt to local environments and have differentiated. The strain from Iriomote-jima (IR) differed from other Japanese strains in the nucleotide sequences of its cytochrome oxidase subunit I (COI) and in not undergoing diapause and having a shorter preimaginal period and a higher adult tolerance of cold. The strains other than IR showed a low level of nucleotide variation in COI but varied in their mode of reproduction; the strains from the Ryukyu Islands were sexual, whereas those from the main islands of Japan and Ogasawara were parthenogenetic. In addition, strains from higher latitudes generally showed a high incidence of diapause, although there were some exceptions. On the other hand, preimaginal period and adult cold tolerance varied little among the strains excluding IR, and pupal cold tolerance, oviposition preference and incidence of parasitism varied little among the strains including IR. Evolution and environmental adaptations in this species are discussed, particularly focusing on parthenogenetic populations.