For identification of insect larvae occurring in galls formed on culms of Sasa kurilensis in Shiga‐kôgen, Nagano and those of Pseudosasa japonica in Takao‐san, Tokyo, we undertook a DNA barcoding analysis using the mitochondrial cytochrome oxidase subunit 1 (CO1) gene. Seventeen operational taxonomic units (OTUs) were identified for larvae from Shiga‐kôgen and one for those from Takao‐san. Of 17 OTUs from Shiga‐kôgen, 10 were most likely assigned to Cecidomyiidae (Diptera), one to Anthomyzidae (Diptera), two to Lepidoptera and four to Hymenoptera. One OTU from Takao‐san was assigned in the Cecidomyiidae cluster. However, none of the OTUs was assigned to known species. It is unknown whether primary gall‐makers are included in the putative cecidomyiid, anthomyzid and lepidopteran species found in this study. However, hymenopteran species occurring in these galls would be parasitoids. How so many cecidomyiid species coexist on bamboo culms in Shiga‐kôgen is an interesting issue and remains to be resolved.

The Drosophila parasitoid system is an excellent model for the study of biological and ecological interactions. In Japan, extensive studies have been carried out on Drosophila parasitoids since the early 2000s. Here we provide up‐to‐date information on their diversity, distributions, host use and reproductive mode. Until now, 45 wasp species have been recorded. In addition, four genetically distinct groups (tentatively assigned as “races”) have been found in Ganaspis brasiliensis (Figitidae). Most of them are larvo‐pupal parasitoids belonging to the families Figitidae and Braconidae, and some are pupal parasitoids of the families Pteromalidae and Diapriidae. A species of Encyrtidae was also recorded. Their major hosts are indicated with information on the host's breeding sites. Except Ganaspis xanthopoda and two races of G. brasiliensis that are distributed both in tropical and temperate regions, they are divided into tropical and temperate species. The tropical species are mainly distributed in Southeast Asia, and their distributions in Japan are restricted to the Ryukyu islands, particularly Iriomote‐jima. The temperate species have been recorded from the main islands of Japan and surrounding islands but not from the Ryukyu islands, except two braconid species, Asobara japonica and Phaenocarpa sp. TK1. Some of the temperate species have also been recorded from Korea, China, Europe and/or North America. Among the 45 Japanese parasitoid species, at least seven are assumed to be thelytokous.

The distribution pattern and competition of insects exploiting Camellia japonica flowers were studied in Tokyo, central Japan, to understand how their distributions are determined. Dasiops sp. of Lonchaeidae (Diptera) exploited flower buds and showed random distribution, whereas Drosophila unipectinata , D. oshimai and D. lutescens of Drosophilidae (Diptera) and Epuraea commutata of Nitidulidae (Coleoptera) exploited fully opened, late and fallen flowers and showed aggregated distribution. From the distribution pattern, it is assumed that Dasiops sp. has clutches of single egg whereas drosophilid and nitidulid species have clutches of more than one egg. In resource supplementary experiments, body size of drosophilid flies increased if resources were supplemented, although their survival is assumed to be unaffected. However, their body size did not decrease with increase of larval density in resource patches. It is therefore unclear whether resource competition occurs among drosophilid flies in Camellia flowers in nature. From the present and previous studies, it is assumed that aggregation (or production of clutches of more than one egg) is related to the use of fermenting or decayed resources; aggregation might increase larval survival and/or performance under the presence of molds or microorganisms.

Distributions and oviposition sites of Drosophila suzukii (Matsumura) and its parasitoids on wild cherry tree were studied in early summer in a suburb of Tokyo, central Japan. Adults of D. suzukii occurred in the foliage layer as well as in the undergrowth layer. The number of D. suzukii that emerged did not significantly differ between wild cherry fruit collected from the foliage layer and those from the undergrowth layer. In addition, the number of D. suzukii that emerged per fruit decreased when fruit were left on the ground longer. It is therefore assumed that D. suzukii females rarely oviposit eggs in fallen wild cherry fruit. The suzukii-associated type of Ganaspis brasiliensis (Ihering) was the major parasitoid that emerged from D. suzukii in the study area. The rate of parasitism by this parasitoid did not significantly differ between larvae in fresh fruit from the foliage layer and those in fallen fruit from the undergrowth layer. This may also suggest that this wasp rarely attacks D. suzukii larvae in fallen fruit. Adults of the suzukii-associated type of G. brasiliensis, Asobara sp. TK1, and Leptopilina japonica that attack D. suzukii were mainly collected from the foliage layer. On the basis of the present results, some proposals for the control of D. suzukii were discussed.

Ganaspis brasiliensis (Ihering) (Hymenoptera: Figitidae: Eucoilinae) is a Drosophila parasitoid that has often been misidentified as G. xanthopoda (Ashmead) in recent studies. This study aims to clarify genetic differentiation of G. brasiliensis based on the nucleotide sequences of the mitochondrial cytochrome oxidase subunit 1 (CO1) gene and three nuclear DNA regions, the inter-transcribed spacers 1 and 2 (ITS1 and ITS2) and putative 60S ribosomal protein L37 (RpL37), as well as crossing experiments. Four lineages are recognized in individuals assigned as G. basiliensis by morphology, (1) individuals occurring in Japan and probably South Korea, (2) individuals from a small subtropical island of Japan, Iriomote-jima, (3) individuals from temperate lowlands of Japan and high altitude areas of Southeast Asia, and (4) individuals occurring widely in Asia, America, Hawaii and Africa. The first lineage is a specialist of Drosophila suzukii (Matsumura), a pest of fresh fruit, and also the fourth lineage has a capacity to parasitize this pest species. The first, third and fourth lineages occur sympatrically at least in Tokyo. The third and fourth lineages differed in mate choice and host use to some extent, but post-mating isolation between them was almost absent.

Illiciomyia yukawai (Diptera: Cecidomyiidae) induces leaf galls on Illicium anisatum (Schisandraceae) and exhibits1-year (yr) and 2-yr type life history patterns. Geographical and annual variations in the proportion of 2-yr to 1-yr type individuals of I.yukawai were studied from 1977 to 1994 and in 2008, 2009 and 2014. An analysis of geographical variation at 13 different census fields indicated that the proportion of 2-yr type individuals significantly increased with the decrease of mean annual temperature reflected by altitudinal and latitudinal gradients. However, a multiple regression analysis indicated that the annual variation in the proportion was not correlated with temperature, gall density, abundance of host resources or parasitism by hymenopteran parasitoids. Thus, we eliminated the effects of these external factors that have been thought to determine the annual variation. We need to take alternative intrinsic factors, instead of external factors, into consideration to explain the annual variation. The fall of galled leaves occasionally caused a higher mortality of 2-yr type individuals than those of 1-yr type. Nevertheless, 2-yr type individuals exist. We considered that the existence of 2-yr type individuals of I.yukawai has an adaptive significance to diversify risks against catastrophic events such as the serious shortage of host buds and high percentage of parasitism that happen more frequently than the high mortality caused by the fall of galled leaves.

Drosophila suzukii is a pest of soft fruit such as cherry, strawberry or blueberry and recently colonized North America and Europe from Asia. In this study, we assessed the utility of Japanese Asobara species as agents for the biological control of this pest species by examining their host use in nature and their capacity to parasitize this pest species. From Japan, eight Asobara species including putative three undescribed species were found; Asobara japonica was recorded from all over Japan, Asobaratabida from high altitude areas in central and northern Japan, Asobararossica and Asobara rufescens from central to northern Japan, three undescribed species from central to western or southern Japan and Asobarapleuralis from a subtropical island of Japan. Among them, an undescribed species Asobara sp. TK1 may be useful as an agent for the biological control because it was recorded only from D.suzukii. All of the remaining seven species were generalists mainly using drosophilid species associated with fermenting fruits, and four of them had no or very low abilities to parasitize D.suzukii, indicating that these seven species are not or less appropriate as agents for biological control.

Wasps of the genus Leptopilina (Hymenoptera: Figitidae) are larvo-pupal parasitoids of Drosophila species. Here we report three putative thelytokous species of this genus from Japan, with description of two new species L.tokioensis and L.tsushimaensis, which have been recorded from central Japan and Tsushima, respectively. Another thelytokous species is L.longipes occurring in northern Japan, although its European populations are assumed to be arrhenotokous. Preliminary phylogenetic analyses suggest the present three species are diversified from one another and also from the other Leptopilina species. These three thelytokous species are infected by B-supergroup Wolbachia as in European thelytokous species, L.clavipes and L.australis. The evolution of these thelytokous species is discussed based on the present and previous results, and the occurrence and distributions of Leptopilina species in Japan and surrounding regions are briefly reviewed.

Ganaspis individuals parasitizing Drosophila suzukii (Matsumura), a pest of fruit crops, 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. They were also different in forewing and antenna morphology, although they showed some overlap in morphological traits. They are tentatively assigned as the suzukii- and lutescens-associated types of G. xanthopoda Ashmead. In the present field survey, Leptopilina japonica Novković & Kimura and some Asobara species were also observed to attack D. suzukii larvae in wild cherry fruit.

The diversity and host associations of parasitoids attacking mycophagous drosophilids were studied in Tokyo (a warm-temperate region) and Sapporo (a cool-temperate region) in Japan. Field collections were carried out using traps baited with mushrooms in May, June, September and October 2009 in Tokyo and in July and August 2010 in Sapporo. The major drosophilid species that emerged from mushroom baits was Drosophila bizonata in Tokyo and D.orientacea in Sapporo. In total, 13 parasitoid species emerged from drosophilids occurring in mushroom baits, and 11 of them were larval parasitoids belonging to Braconidae and Figitidae. Among the 11 larval parasitoids, 10 were collected in Tokyo, while only two were collected in Sapporo. It is not known why their diversity differed so much between these two regions. Four of the 11 larval parasitoids have also been recorded from drosophilid larvae occurring in fruit (banana). The use of these two habitats (mushrooms and fruit) by these four species seems to reflect the occurrence (i.e. resource use) of their suitable hosts. On the other hand, most larval parasitoids from Tokyo attacked D.bizonata, and two larval parasitoids from Sapporo attacked D.orientacea, suggesting that the abundance of potential hosts is one of the important factors affecting their host use.

Seasonal occurrence of adult phorid flies was studied in and near Tokyo from 1990 to 1992 using traps baited with pork. The collected 20 species were categorized into 6 types. Megaselia sp.1 was collected chiefly in early spring and late autumn (Type I). Three species, Anevrina unispinosa, Hypocera anularia and Plethysmochaeta nobilis, were collected chiefly in mid and late spring (Type II). Conicera sp., Diplonevra abbreviata and Woodiphora sp. were collected in summer (Type III). Two domestic species, Megaselia scalaris and M. spiracularis, were collected from summer to autumn (Type IV). Gymnophora pararcuata was collected only in October (Type V). The remaining 10 species, Conicera formosensis, Diplonevra peregrina, Dohrniphora cornuta, Megaselia deningi, M. sp.2, Puliciphora obtecta, P. tokyoensis, Spiniphora atricostata, Triphleba nipponica and Woodiphora kuenburgi, were collected from spring to autumn constantly (Type VI).

To understand the factors governing the diversity, abundance and host associations of parasitoids attacking frugivorous drosophilid flies on Iriomote-jima, a subtropical island of Japan, we monitored parasitism on several occasions over the period 2003-2009. Fifteen drosophilid and 12 parasitoid species were recorded. Three species of Drosophila, D. bipectinata, D. albomicans and D. takahashii, bred abundantly in banana baits, though their abundance varied between years and seasons. Frequent parasitoid species were Asobara japonica, A. pleuralis (Braconidae), Leptopilina ryukyuensis and L. pacifica (Figitidae). L. victoriae was recorded only in December 2003. In addition, host acceptance and host suitability of the four most frequently recorded parasitoid species were studied in the laboratory. Most parasitoid and drosophilid species showed species-specific associations with more than one antagonist species, suggesting that they have been subjected to complex coevolutionary interactions. In addition, host range of most of the parasitoid species included one of the three major Drosophila species, suggesting that the abundance of potential hosts is one of the factors determining the evolution of parasitoid host use.

Despite the intensive use of the Leptopilina genus and its drosophilid hosts as model systems in the study of host–parasitoid interactions, the diversity and distribution of the species occurring in the Asian region remain elusive. Here we report the phylogeny of Japanese Leptopilina species attacking frugivorous drosophilid flies, based on COI, ITS1 and ITS2 sequences. Consistent with molecular data, hybridization experiments and morphological examination, five species were recorded in Japan: Leptopilina heterotoma , L. victoriae and three new species, two occurring in the Ryukyu archipelago, L. ryukyuensis and L. pacifica , and another species, L. japonica , distributed in Honshu and Hokkaido. Leptopilina japonica is further divided into two subspecies, L. j. japonica occurring in Japan, and L. j. formosana occurring in Taiwan. According to these results, we discuss the evolution, speciation and colonization history of Japanese Leptopilina species.

Seasonal life cycles and resource uses of flower- and fruit-feeding drosophilids (Diptera: Drosophilidae) were studied from low to high altitudes in central Japan to understand their adaptation to seasonal changes of environmental conditions. Drosophila unipectinata and D. oshimai specialized to flowers, D. suzukii and D. subpulchrella depended almost on fruits, while D. lutescens, D. rufa, D. auraria, D. biauraria and D. sternopleuralis used both of them. It was assumed that D. unipectinata moved from low to high altitudes in June while D. oshimai, D. suzukii and D. subpulchrella in July. Migration of D. unipectinata is considered as a means to avoid summer heat or exploit early-summer resources at high altitudes. On the other hand, D. oshimai, D. suzukii and D. subpulchrella have the capacity to pass the summer at low altitudes, and therefore their migration is assumed as a means to escape from resource-poor conditions in summer at low altitudes or exploit resources at high altitudes. The generalist species, D. lutescens, D. rufa, D. auraria, D. biauraria and D. sternopleuralis, would not perform such extensive movements between low and high altitudes. They may pass the summer at low or mid altitudes depending on accidentally fallen immature fruits and/or some other resources such as decayed leaves.

In central Japan Ganaspis xanthopoda and Asobara japonica commonly parasitize the larvae of frugivorous drosophilids, mainly in montane forests, and urban environments and small groves, respectively. These two parasitoids start reproduction about one month later than their host drosophilids, probably to avoid searching for hosts when host density is low in early spring. It is likely that the local variation in the abundance of these parasitoids and a temporal refuge for their hosts contribute to the persistence of this parasitoid-host community. The forest species, G. xanthopoda, parasitized at least three Drosophila species that are abundant in forests, supporting the hypothesis that parasitoids are better adapted to attack frequently-encountered host species. This parasitoid did not parasitize drosophilid species that are phylogenetically distantly-related to the three host species or less frequent in forests. Benefits of using such species as host would not exceed the costs of evolving virulence to them. Another parasitoid, A. japonica, parasitized various indigenous and exotic drosophilid species including those that it rarely encountered in the field. It is not clear why this species has such a wide host range.

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.

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.

In Japan, dominant parasitoids attacking frugivorous Drosophilidae species were Asobara (Braconidae, Alysiinae), Leptopilina, and Ganaspis species (Figitidae, Eucoilinae). Asobara japonica was found throughout Japan, and its populations in the main islands of Japan were parthenogenetic whereas those in the subtropical islands were sexually reproducing. Other parasitoids showed rather restricted distributions; A.tabida, A. rossica, A. rufescens, and Leptopilina heterotoma occurred mainly in northern to central parts of the main islands, Ganaspis xanthopoda from central to southern parts of the main islands, A. leveri in a southern part of the main islands, and A. pleuralis, L. victoriae, and Ganaspis sp. mainly in the subtropical islands. Their major hosts were species of the D. melanogaster species group in the main islands, and species of the D. melanogaster, immigrans, and polychaeta species groups in the subtropical islands. Host use considerably varied among parasitoid species, especially in the subtropical islands.

In the aggregation theory, aggregation of eggs is one of important conditions for the coexistence of species. However, aggregation of eggs by clutch laying does not always promote coexistence, whereas aggregation of eggs by aggregated distributions of ovipositing females always has a significant contribution to the coexistence. In this study, spatial distributions of three Drosophila species across naturally occurring cherry fruits were studied with relation to their clutch sizes. Drosophila suzukii oviposited eggs mainly on fresh fruits on trees, and its eggs were randomly distributed across cherry fruits. The emergence data also indicated random spatial distributions of this species. Random egg distributions of this species are explained by random visits of females to fruits and the production of clutches of mostly single eggs. On the other hand, D. lutescens and D. rufa oviposited on fallen fruits, showed aggregated distributions in the emergence data, and frequently produced clutches of a few eggs. In these species, the degree of aggregation was usually significantly lower than the expectation based on random visits of females to fruits and their clutch sizes observed in the present experiments, indicating that their aggregation is unlikely to arise from aggregated distributions of ovipositing females. Thus, the spatial aggregation of these species does not necessarily lead to their coexistence.

Periodical surveys using traps baited with minced pork were carried out once a month in 1990-1992 in central Japan. In this study, 8 calliphorid and 10 sarcophagid carrion-breeding species were collected. In general, calliphorid species preferred forests, while sarcophagid species preferred open areas.