In order to evaluate the magnitude of insect invasion indoors under various light conditions, we compared light trap catches; one was set up outdoors, and the other was set up indoors in such a way that it did not leak its light to the outside. The ratio of the number of insects invaded that indoors to those captured with the outdoor light trap was used to evaluate invasion level because a positive correlation was found between them, and the number of insects that invaded indoors increased with the increase in those captured with the outdoor light trap. With a 10 cm open slit in the window, the ratio when both the room lights and the indoor light trap were turned on (4.1%) did not significantly differ from the ratio when only the room lights were turned on (5.7%). The ratio when neither the room lights nor the indoor light trap were turned on (0.6%) did not significantly differ from the ratio when only the indoor light trap was turned on (0.5%). Furthermore, the ratios were significantly higher under the former two conditions (4.1 and 5.7%) than under the latter two conditions (0.6 and 0.5%). Thus, the invasion of insects indoors was determined to be dependent on room light, and the indoor light traps did not affect the invasion of insects from outdoors.
The relationship between larval instar and head-capsule width in Helicoverpa armigera (Hübner) was examined in laboratory-reared and field-collected insects from Ibaraki and Yamanashi in eastern Japan. Each of the first three and each of the last three instars could reliably be distinguished using head-capsule width for both strains fed on an artificial diet. In the laboratory, 91.8% of larvae from Ibaraki had five instars, and 8.2% had six or seven instars, while 36.1% of the larvae from Yamanashi had five instars, and the rest had six instars. Pupation occurred when the larval head-capsule width reached about 2.6 mm, and the development time for each instar was independent of the total number of instars. Consequently, head-capsules were typically larger at each instar for larvae with fewer instars. The distribution of head-capsule widths in larvae obtained from sunflowers in Ibaraki showed peaks corresponding to the first, penultimate, and ultimate instars of laboratory-reared larvae. However, the widths supposedly representing the second and third instars were smaller than those found in the laboratory, suggesting that H. armigera larvae molt more times in the field than in the laboratory and require a longer time to complete development on sunflowers. These results may enable improvement of H. armigera forecasting and insecticide bioassay tests.
Adult Sympetrum infuscatum (Selys) live in the forest gaps throughout their life except when visiting rice paddy fields for oviposition. They prey on small flying insects in the forest gaps, using sit-and-wait tactics. They perch on the tips of branches or grass all day and take off when a small flying insect comes into sight. In the present study, the foraging behavior of S. infuscatum in the forest gaps was observed. The perching height was high in the morning and evening and low around noon. The diurnal change in the perching height corresponded to the abundance of flying small insects. The mean daily frequency of foraging flights was 251 for females and 182 for males, and the mean actual number of insects captured was 109 and 89, respectively. A total of 2,935,300 small flying insects were preyed on by S. infuscatum adults during one day in the Satomaya forest gaps.
We demonstrated that a synthetic sex pheromone, 2-isopropyliden-5-methyl-4-hexen-1-yl butyrate, disrupted the mating of the Japanese mealybug Planococcus kraunhiae (Kuwana) (Hemiptera: Pseudococcidae). The synthetic pheromone was impregnated into grey rubber septa. In the presence of the synthetic pheromone, the copulation rates of reared P. kraunhiae were significantly decreased in a plastic case (diameter: 8 cm, height: 6 cm), an insect net cage (each side: 95 cm), and a small scale orchard (9 m2). In Japanese persimmon orchards (4~5 a), the dispersion of high concentrations of the synthetic sex pheromone disturbed male orientation, leading them towards the pheromone traps, and consequently reduced the number of females that copulated. In the persimmon orchard, mating disruption based on the synthetic pheromone successfully controlled the population density of P. kraunhiae in the next generation.
We examined the acquisition and transmission rates of Tomato spotted wilt virus (TSWV) in Frankliniella occidentalis that were fed with eight TSWV-infected weed species. When the first instar larvae were given TSWV-infected leaves of Cerastium glomeratum, Solanum nigrum, Stellaria media, and Galinsoga ciliata, the acquisition rates of adult thrips were 85.4%, 73.6%, 72.6%, and 35.6%, and the transmission rates were 76.4%, 60.9%, 61.3%, and 29.9%, respectively. On the other hand, the acquisition and transmission rates were less than 10% when F. occidentalis were fed with Lamium amplexicaule, Stellaria neglecta, Veronica persica, and Vicia angustifolia. These results suggest that the potential to be an TSWV-acquisition source for F. occidentalis differs among weed species, and that the thrips can become transmitters by acquiring the virus from some weed species.
In June 2005, an unidentified species of Dasineura (Diptera: Cecidomyiidae) that induced leaf-fold galls on cultivated roses was found in a greenhouse in Heguri, Nara Prefecture, Japan. Similar Dasineura species have been known to occur in Japan on two wild roses, Rosa multifolia and R. rugosa. In Europe, rose leaf midge, Dasineura rosae, induces leaf-fold galls on both cultivated and wild roses. In order to confirm the phylogenetic relationship among Rosa-associated Dasineura species, we analyzed a partial region of the mitochondrial DNA cytochrome oxidase subunit I (676 bp) gene. The nucleotide sequence of the Dasineura species collected from cultivated roses in Nara was identical to that of gall midges that induced leaf-fold galls on wild R. multiflora in Nara and Kyoto Prefectures, Japan. However, D. rosae and Dasineura sp., which are associated with R. rugosa, were phylogenetically distinct from them. This indicates that the Dasineura sp. associated with wild R. multiflora has invaded the greenhouse in Nara Prefecture and infested the cultivated roses.
The time of development from egg to pupal stage of four native parasitoid species, Neochrysocharis formosa, Hemiptarsenus varicornis, Diglyphus isaea and Chrysocharis pentheus, on a native leafminer species, Chromatomyia horticola, and an exotic leafminer species, Liriomyza sativae, was examined in a laboratory. The developmental time of N. formosa and H. varicornis did not differ significantly between the two host leafminer species, but that of D. isaea differed slightly. The developmental time of C. pentheus on L. sativae was significantly longer than that of C. horticola. The present findings suggest that L. sativae and C. horticola may have similar suitability as a host for N. formosa, H. varicornis and D. isaea, but not for C. pentheus.