Ken Tabuchi

Inter- and Intraspecific Comparisons Between Asteralobia Gall Midges (Diptera: Cecidomyiidae) Causing Axillary Bud Galls on Ilex Species (Aquifoliaceae): Species Identification, Host Range, and Mode of Speciation

Abstract Inter- and intraspecific differences between Asteralobia gall midges (Diptera: Cecidomyiidae) that induce axillary bud galls on several Ilex species were studied from morphological, molecular, and ecological points of view. Asteralobia sasakii (Monzen) and Asteralobia soyogo (Kikuti) were clearly distinguished from one another by thoracic setal and scale counts and by sequences of partial mitochondrial DNA cytochrome oxidase subunit I region. Because adults of A. sasakii emerged within a shorter period of time and later in the season than those of A. soyogo, they were considered to be temporally isolated. The host ranges of A. sasakii and A. soyogo did not overlap. A. sasakii was confirmed to use Ilex crenata Thunberg, Ilex crenata var. paludosa (Nakai) Hara, and Ilex maximowicziana Loesener for galling, and A. soyogo included galls on Ilex chinensis Sims, Ilex integra Thunberg, Ilex leucoclada (Maximowicz) Makino, and Ilex pedunculosa Miquel. Molecular phylogenetic analysis revealed that host races were not formed either in A. sasakii or in A. soyogo populations, whereas geographical variations were detected for both species at the DNA level. The haplotype diversity was significantly higher in A. soyogo than in A. sasakii. The DNA analysis suggested that A. sasakii and A. soyogo had speciated allopatrically. On the basis of the current study, we concluded that A. soyogo had been already established in Honshu, Shikoku, and Kyushu, Japan, when A. sasakii arrived in these areas from the southwest islands more recently.

Locomotion Ability Variation Among Instars of the Bean Bug, Riptortus pedestris (Fabricius) (Heteroptera: Alydidae) Nymphs

Abstract The nymphal locomotion ability (walking distance) of the stenophagous bean bug Riptortus pedestris (Fabricius) was studied in each instar. We measured the walking distance using two systems. The walking distance in photophase was measured for 6 h using a tracking system with a charge coupled device (CCD) camera and computer software. The daily activity of nymphs was measured by an actograph system counting the number of infrared beam intercepts. The actograph data were converted to distance using a linear regression against the data of the tracking system. The longevity of nymphs without food was also studied to estimate the potential walking distance. Using both the tracking and actograph systems, it was determined that first instars walked less than the other instars (only 10.7 m within 6 h). The second to fifth instars could move 20–25 m within 6 h, and this distance did not differ among instar. This indicates that first instars seldom move after hatching in the field. The walking distance for 24 h varied and was greatest for the third instars (80.8 m). The potential longevity of nymphs was found to increase with instar age. Potential locomotion ability (walking distance for 24 h × potential longevity) was high in the third to fifth instars (≈340 m). The potential locomotion ability for the second instars was relatively low compared with the elder instars (≈180 m). From these results, nymphs of R. pedestris seem to adapt by identifying feeding site locations after hatching and elder instars may be able to find a novel feeding site after the degradation of previous habitat.

Abundances of a bean bug and its natural enemy in seminatural and cultivated habitats in agricultural landscapes.

ABSTRACT To determine differences in distribution patterns between the soybean pest Riptortus pedestris F. (Hemiptera: Alydidae) and its egg parasitoid Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) in source and cultivated habitats, we compared their abundances in soybean fields and forest edges, which were assumed to be the overwintering sites of R. pedestris. We set synthetic attractant-baited traps for both species over 2 yr in mid-August, just before R. pedestris normally colonizes soybeans. During one of the 2 yr, we also examined the rate of parasitism using an egg trap. The numbers of both R. pedestris and O. nezarae trapped at forest edges were higher than the numbers caught in soybean fields, suggesting that forest edges are important source habitats. Compared with R. pedestris, the abundance of O. nezarae in soybean fields was considerably lower than in forest edges, presumably because of differences in their dispersal abilities and their responses to landscape structure and resource distribution. Better pest control service by O. nezarae was provided at forest edges than in soybean fields. Therefore, when using pest control by O. nezarae in soybean fields, spatial arrangement and distance from the forest edge should be considered.

Seasonal Trends of Forest Moth Assemblages in Central Hokkaido, Northern Japan

ABSTRACT. Seasonal trends of adult moth assemblages were investigated using portable light traps in a cool-temperate region in central Hokkaido, northern Japan. Light traps were set at monthly intervals from April to December 2005 in five stands. Seasonal changes in the numbers of species and individuals in each stand were unimodal with a peak in summer (July or August). The value of a similarity index between samples from successive months in each stand was always low, indicating that species composition changed greatly between successive months. Based on the seasonal occurrence of 248 species, the mean occurrence period in each species was only 1.8 months. Among these species, 91.5% were estimated to be univoltine and only 8.5% were estimated to be multivoltine. Most species occurred in the summer (July and/or August), although some occurred only in the spring or autumn. Thus, in the present study the high species turnover of adult moths during the active season was due to the short occurrence period of each species, which may be associated at least in part with univoltinism, synchronized adult eclosion, and short life spans of adult moths.

Deer Browsing on Dwarf Bamboo Affects the Interspecies Relationships among the Parasitoids Associated with a Gall Midge

We found that deer browsing alters the species composition of parasitoids of gall-forming insects via its effects on the host plants. At Mt. Odaigahara, in west-central Japan, we compared the species composition of two parasitoid wasps, Pediobius sp. (Eulophidae) and Torymus sp. (Torymidae), on an unidentified gall midge (tribe Oligotrophini) that forms galls on dwarf bamboo (Sasa nipponica Makino et Shibata), the major forage for Sika deer (Cervus nippon Temminck). Gall width was larger inside deer exclosures, where the bamboo culms were longer and thicker due to their escape from browsing. The parasitism rate by Pediobius sp. was lower inside the exclosures, where parasitism concentrated on the smaller galls. In contrast, the parasitism rate by Torymus sp. was higher inside the exclosures and concentrated on the larger galls. Torymus sp. emerge earlier and have a longer ovipositor than Pediobius sp., thus it should be able to oviposit throughout all gall developmental stages. Because Torymus sp. may be hyperparasitized by Pediobius sp., more Torymus sp. larvae survived in larger galls that Pediobius sp. could not penetrate with its shorter ovipositor. Thus, deer browsing indirectly favors Pediobius sp. by reducing gall size and thereby improving access to host.

Short-Term, Efficient Sampling Strategies for Estimating Forest Moth Diversity Using Light Traps

ABSTRACT Evaluation of species diversity for highly diverse taxa is extremely time-consuming and costly; thus, there is a need to develop efficient sampling strategies. We established a short-term, efficient sampling scheme to produce samples that represent a full-season sampling of moth assemblages with a high degree of seasonality. We sampled adult moths monthly for the duration of the moth flying season by using light traps in five forest stands in a cool-temperate region in central Hokkaido, northern Japan. From this sample, we generated various subsamples that reduced the sampling period and the number of traps per stand, and tested whether these subsamples provide estimates of species richness, abundance, and species turnover representative of those revealed by the whole season sample. Comparisons between the whole season sample and each subsample indicated that setting one light trap on a night in July and August, which shortened the sampling period to 25% and reduced sample size to 38%, was the most efficient sampling scheme to estimate abundance, species richness, and similarity in the whole season sample. The comparisons also suggest that it is efficient to use rarified species richness as a species richness estimator, and the Bray—Curtis index or Morisitas C&lgr; for estimating species turnover between sites in moth assemblages.

Description of a new Procystiphora species (Diptera : Cecidomyiidae) inducing galls in culms of Sasa nipponica (Poaceae) in Japan, and the first discovery of an inverted ovipositor in Diptera

Procystiphora uedai sp. nov., a cecidomyiid inducing subglobular galls on Sasa nipponica Makino and Shibata on Mount Ôdaigahara, Nara Prefecture, Japan is described herein. This species is distinguishable from the three known congeners by the following characteristics of the female post‐abdomen: tergite VIII concave at both anterior and posterior margins; tergites VII, VIII and sternite VII unsclerotized; ovipositor–dorsoventrally inverted. Most individuals of this gall midge are univoltine and pupate in the galls in early September, but some individuals enter prolonged diapause at the third larval stadium and remain in the mature galls until the following year. Larvae of this species are attacked by two parasitoid species, Pediobius sasae Hansson (Eulophidae) and Torymus sp. (Torymidae).

Different Oviposition Strategies in Two Closely Related Gall Midges (Diptera: Cecidomyiidae): Aggregation versus Risk Spreading

The oviposition strategies were compared between two closely related gall midges, Asteralobia sasakii and A. soyogo (Diptera: Cecidomyiidae). They induce spherical, multilocular galls on the axillary buds of Ilex species (Aquifoliaceae). A. sasakii is known to have a narrower host range and induce larger galls that contain more numerous larvae than A. soyogo. The large A. sasakii galls have been considered to act as physical barriers to protect larvae from ectoparasitoid attack. We observed that A. sasakii induced galls more frequently on the axillary bud at the tip of the shoot, indicating that the females concentrated their eggs at a single oviposition site. In contrast, A. soyogo induced several small galls in a shoot, scattering their progeny. The number of A. sasakii galls per shoot was significantly smaller than that of A. soyogo. Our current observation, together with the previous data, demonstrates that A. sasakii lays eggs in clusters to lessen the threat of ectoparasitoid attack (aggregation), whereas A. soyogo spread the risk to progeny by scattering eggs in a single shoot using several host plant species (risk spreading). The oviposition strategy of A. soyogo also seems to be supported by its diversified life cycles with a polymodal emergence pattern.

Detecting crucial dispersal pathways using a virtual ecology approach: A case study of the mirid bug Stenotus rubrovittatus

Detecting dispersal pathways is important both for understanding species range expansion and for managing nuisance species. However, direct detection is difficult. Here, we propose detecting these crucial pathways using a virtual ecology approach, simulating species dynamics using models, and virtual observations. As a case study, we developed a dispersal model based on cellular automata for the pest insect Stenotus rubrovittatus and simulated its expansion. We tested models for species expansion based on four landscape parameters as candidate pathways; these are river density, road density, area of paddy fields, and area of abandoned farmland, and validated their accuracy. We found that both road density and abandoned area models had prediction accuracy. The simulation requires simple data only to have predictive power, allowing for fast modeling and swift establishment of management plans.