Immediately after first mating, the bursa copulatrix of female Stenotus rubrovittatus expanded with a white bulbous spermatophore, which was not observed in unmated females. Sperm was present in the head portion of the spermatophore. The spermatophore was observed in all females immediately after mating and the following day. From 3 to 7 days after mating, the number of females with the spermatophore decreased from 93% to 30%, and most spermatophores shrank to a goblet shape. Sperm in the lateral oviduct was observed in over 96% of females until 7 days after mating. Spermatophores were also present in mated females that were preserved in 70% ethanol for several weeks. In the male genital organs, opaque white parts were present in the accessory glands of unmated males, but were absent immediately after mating. These differences suggest that a secretion from the male accessory gland enters the female bursa copulatrix with the sperm during mating, and the spermatophore is formed temporarily. The mating experience of females can be ascertained by observation of the sperm and/or the spermatophore, which is easy to distinguish in the genital organs.

View full abstract

To evaluate the cold-hardiness of the rice water weevil (RWW), Lissorhoptrus oryzophilus, supercooling points were measured, and RWW's mortality after continuous and intermittent exposure to moderately low temperatures was investigated using field-collected overwintering adults. RWW was freezing intolerant. The mean supercooling points in dry and wet conditions were −15.2°C and −10.5°C, respectively. One-time exposure of RWW to −10°C for 3 h made no difference in the supercooling points. The effect of repeated exposure to −10°C for 3 h differed greatly between dry and wet conditions. The mortality rate was 30.5% after 12 treatments under dry conditions, yet it reached 100% after 7 treatments under wet conditions. In wet conditions, the mortality of adults exposed continuously to −3°C or −5°C for 10 to 120 days was at most 7.5%, while exposure to −10°C for 20 days resulted in 100% mortality. These results reveal that RWW adults suffer much higher mortality in wet conditions than in dry conditions and that overwintering would be difficult for RWW in wet conditions if they were exposed repeatedly or continuously for a long period to −10°C. Improvement in the forecasting of RWW occurrence is discussed on the basis of the results obtained.

View full abstract

Kudzu, Pueraria montana (Lour.) Merr. var. lobata (Willd.) Maesen et S. Almeida, is an invasive weed introduced to the United States from Japan. In Japan, we conducted an intensive search of biological control agents for kudzu in 2004 and 2005. Through field survey and literature research, we found 48 species of potential kudzu feeders, including 20 species which have not been recorded in a previous list of arthropods associated with kudzu in Japan. Of the 20 species, 3 species, Reptalus quadricinctus Matsumura, Paracardiophorus subaeneus yasudai Ohira and Jodis orientalis Wehrli, were considered as possible monophagous kudzu feeders. Numbers of common species between Japan and China, and between Kinki District, central Japan and Kagoshima City, southern Japan were 15 and 21, respectively. The small numbers of common species showed large difference of insect fauna among native range of kudzu. In our search in Kinki District, the cumulative number of species found by cumulative searching time almost reached saturation by ca. 2,000 min search. This suggests that survey over wider geographic range and/or in different design would be required for more efficiency in future surveys of potential biological control agents of kudzu in Japan.

View full abstract

The tea-infesting population of Aleurocanthus spiniferus (Quaintance), which has spread to tea gardens in Japan since its discovery in 2004, was differentiated from the citrus-infesting population, which was identified in Japan in 1922, by polymerase chain reaction (PCR) of the mitochondrial cytochrome c oxidase subunit I (mtCOI) gene. Sequences of mtCOI differ between the tea- (assessed in 27 tea gardens in 14 prefectures) and citrus-infesting populations (evaluated in 11 citrus orchards in 8 prefectures); no variations were noted within each population, and the base identity between the populations was 78.0% (674 base pairs). Additionally, individuals from Camellia sasanqua, Eurya japonica, Illicium anisatum, and Zanthoxylum piperitum were identified as belonging to the tea-infesting population and individuals from Caesalpinia crista were identified as belonging to the citrus-infesting population. The 2 populations can be distinguished by PCR with specific primers.

View full abstract

To elucidate the annual lifecycle of the bean bug, Riptortus pedestris Fabricius, especially its characteristics on potential host plants before it attacks soybeans, we investigated the seasonal prevalence of the bean bug in Chinese milk vetch, red clover, and soybean fields from 2004 to 2008. In Chinese milk vetch fields, adults of R. pedestris appeared from late April, and their progenies appeared from mid-May to mid-June. The population densities of adults and nymphs in Chinese milk vetch fields varied considerably among years and locations. In red clover fields, immigration of adults varied among years. The adults appeared from late May to early July, and nymphs were found from late June to early July. Adults and nymphs were found in red clover fields until late August to mid-October. In soybean fields, there were no differences in the immigration and population density of adults and nymphs by year. Following adults, nymphs appeared from late July to early August in soybean fields. The nymphs were found in soybean fields until mid-October and the adults were found in the fields until mid-November, respectively. Nymphs and adults of the next generation appeared on each host plant, indicating that R. pedestris can complete its annual lifecycle using Chinese milk vetch, red clover and soybean as successive host plants.

View full abstract

From April to October 2010, native predatory mites (Acari: Gamasina) were collected every 10 days from spinach-cultivated soils of 6 greenhouses located in Hokkaido. From the 14 species collected, Ascidae sp.1, Ascidae sp.2, Hypoaspis (Gaeolaelaps) sp., Cycetogamasus diviortus (Athias-Henriot), Parholaspulus alstoni Evans, Macrocheles sp., and Rhodacaridae sp. dominated in frequency of occurrence. In October 2010, 8 predatory mite species were collected from the soils of 5 greenhouses where spinach was not grown; of these species, 5 were different from those collected from spinach fields.

View full abstract

The effectiveness of carbon dioxide for use as an insecticide was examined by exposing adults and larvae of the western flower thrips (Frankliniella occidentalis) to high concentrations of the gas. Treatment of adults with 20 to 30%CO₂ for 24h at 24°C resulted in a proportional increase in mortality, reaching 100% at 30%CO₂ or higher concentrations. The time required for 100% mortality at 60%CO₂ was less than 24h at 24°C, less than 10h at 30°C, and less than 4h at 34°C. The findings indicated that mortality increased in proportion to carbon dioxide concentrations and treatment temperatures, and that this tendency was common to adult and larval stages. It therefore seems advisable for treatment with high concentration CO₂ to be applied to nursery systems for “thrips-free seedlings.”

View full abstract

The Asian citrus psyllid Diaphorina citri is an important vector of citrus greening disease (Huanglongbing). We investigated its dispersal pattern on Citrus depressa by no-choice and choice tests to determine the risk of the spread of Huanglongbing. D. citri began to disperse from a released tree to another tree 4–5d after adult emergence. The dispersal movement of adults was more active on trees with newly developing buds. Choice testing between trees with and without buds revealed that released adults preferred trees with buds over the 2d test period. This preference disappeared when both trees were treated with a sticky spray to prevent adult movement between trees. These results suggest that adult D. citri do not select trees with new buds from a distance but recognize them by random movement between trees.

View full abstract