Abstract. 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][2004][2005][2006][2007][2008][2009] 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.

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.

No abstract

Blooms of moon jellyfish Aurelia aurita s.l. occur in various vertical distribution patterns within the water column. Reasons for these distribution patterns have remained obscure. To quantify the influence of pycnocline and low dissolved oxygen (DO) on the vertical distribution of A. aurita aggregations, we investigated temperature, salinity, DO, and observed densities of A. aurita at 1-2 m depth intervals via video camera in a eutrophicated, enclosed bay, Mikawa Bay, Japan, for 3 years. During the observed period, stratification and hypoxic status of the bay varied seasonally and interannually due to climatic events, such as rainy season and typhoon passage. Both sharp pycnocline and low DO limited A. aurita vertical distribution. The more strongly stratified the water column, the more the upper boundary of A. aurita distribution was restricted. Bottom hypoxic water limited the lower boundary of A. aurita distribution. The DO threshold for in situ distribution was estimated to be *2.5 mg l -1 , which is much higher than the experimentally obtained, sublethal values identified in previous studies. Our results show that climatic events affect A. aurita vertical distribution through changes in the physical characteristics of the water column.

Diapause and cold tolerance are essential for temperate insects to pass the winter, with the mechanisms controlling these two traits varying considerably among insects. In the present study, diapause and cold tolerance are compared among three Leptopilina species: Leptopilina japonica Novković & Kimura, Leptopilina victoriae Nordlander and Leptopilina ryukyuensis Novković & Kimura, all larval parasitoids of frugivorous drosophilid flies, with the aim of understanding their climatic adaptations. The first species is divided into the temperate (Leptopilina japonica japonica) and subtropical subspecies (Leptopilina japonica formosana), and the latter two species are distributed in the tropical and subtropical regions. The temperate subspecies of L. japonica enters prepupal diapause at low temperatures (15 or 18 °C), irrespective of photoperiod, and some individuals enter diapause when exposed to 0 °C for 1 or 2 day(s) or when placed at low humidity. Leptopilina victoriae also shows signs of diapause initiation at 15 °C, although L. ryukyuensis and L. j. formosana from the subtropical regions do not. Preimaginal viability at low temperature (13, 14 or 15 °C) is usually lower in L. victoriae from the tropical regions compared with L. japonica or L. ryukyuensis from the temperate or subtropical regions. Diapausing prepupae of the temperate subspecies appear to be cold tolerant. However, the cold tolerance of nondiapausing prepupae, pupae and adult females varies little among the tropical, subtropical and temperate species or subspecies, and adult males of the temperate subspecies of L. japonica are less cold tolerant than those of the tropical or subtropical species or subspecies. Cold tolerance may be unnecessary, except for diapausing individuals of the temperate species, because nondiapausing individuals appear in warmer seasons.

Study of the ascidian collection at the National Museum of Nature and Science, Tsukuba, revealed some Japanese specimens of the non-native ascidian, Ascidiella aspersa (Müller, 1776), collected in 2007 from both mid-temperate Oominato, Mutsu Bay, in the northernmost part of Honshû, and from warm-temperate Ago Bay, Kii Peninsula, middle Honshû. These specimens were collected one year earlier than the previous earliest Japanese record from cool-temperate Funka Bay, Hokkaido. Mutsu Bay has an international port, which can be assumed to be the invasion gateway for this ascidian from abroad. On the other hand, this ascidian may have arrived at Ago Bay by domestic transport because all of the bay's ports are strictly for domestic use under governmental regulations. A comparison of the publicly available sequences for the 18S rRNA gene among this species and its allies suggested the possibility that it inhabited Korean waters as far back as the late 1990s, and it entered Japanese waters from Korea through an as yet unknown international port(s).