Seiichi Moriya

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.

Influence of the introduced parasitoid Torymus sinensis (Hymenoptera: Torymidae) on T. koreanus and T. beneficus as indigenous parasitoids of the chestnut gall wasp Dryocosmus kuriphilus (Hymenoptera: Cynipidae) on chestnut trees in Nagano Prefecture, Japan

We describe here the parasitoid wasps Torymus sinensis Kamijo and T. beneficus Yasumatsu & Kamijo (early-spring and late-spring strains), which are introduced and indigenous natural enemies of the chestnut gall wasp Dryocosmus kuriphilus Yasumatsu, an invasive chestnut pest in Japan. We recently discovered specimens of T. koreanus Kamijo, endemic in Korea, among Torymus parasitoids collected from D. kuriphilus galls in a Japanese chestnut orchard. In this study we compare the composition of Torymus parasitoids emerging from D. kuriphilus galls before and after the release of T. sinensis. Before the release of T. sinensis, early-spring and late-spring strains of T. beneficus predominated (58.3 and 20.8% of specimens collected). However, a few years after the release, both T. beneficus strains had been almost completely displaced by T. sinensis. In contrast to the rapid decrease in T. beneficus, T. koreanus did not decrease drastically before and even after the release of T. sinensis (approximately 10–20% of specimens collected). These results suggest that not a few T. koreanus were present in the Japanese chestnut orchard investigated at least several years after the release of T. sinensis, although both the T. beneficus strains were rapidly displaced by T. sinensis during this period.

Heterologous Expression of Corn Cystatin in Soybean and Effect on Growth of the Stink Bug

The bean bug (Riptortus clavatus) is a serious insect pest of soybean. Corn (maize) cystatin strongly inhibited the activity of its digestive cysteine proteinase. Heterologous expression of corn cystatin in soybean seeds inhibited the insects proteases, but not its growth.