Japanese Journal of Applied Entomology and Zoology Vol. 61(2017) No. 3

We investigated the effects of changes in the density of rice skipper Parnara guttata guttata Bremer et Grey larvae in paddy fields on the damage caused during the cultivation of forage rice for whole-crop silage. Young instar larvae were released in mesh cages on late-transplanted rice plants. The larvae were reared in the cages until the pupal stage. After removal of the insects, rice plants at the yellow ripening stage were harvested and dried, and the number of panicles and dry weight of panicles and straw were measured. The total digestible nutrients content of the rice plants was also estimated. Dry matter weight decreased with increasing larval density on the rice plants, whereas total digestible nutrients content did not decrease significantly. Thus, P. guttata guttata may cause quantitative damage to forage rice, but the qualitative damage it causes is relatively small.

Lethal effects of concentrated CO₂ at 40°C on adult females and eggs of Tetranychus urticae Koch were examined. No adult female survived after 6-h exposure to 60% CO₂, and almost all eggs at different ages died after 6-h treatment with 60% CO₂. No marked increase in CO₂ tolerance was observed as the egg stage progressed. These results suggest that both adult females and eggs of T. urticae can be controlled with the same CO₂ treatment at a high temperature.

Earlier studies have demonstrated that Paederia foetida L.（skunk vine）harbors larger numbers of phytoseiid mites for longer periods than any other wild plant in peach orchards. To assess the effectiveness of P. foetida in spider mite control, first, longevity and fecundity of Tetranychus kanzawai Kishida were examined in the laboratory using P. foetida and Phaseolus vulgaris L. as host plants. Results showed that all T. kanzawai larvae died without molting and that female adults laid few eggs on P. foetida. No such adverse effect on larvae or female adults was observed on P. vulgaris. Then, population surveys of spider mites and phytoseiid mites were conducted on peach trees with and without P. foetida. Results showed that the presence of P. foetida itself was inadequate to achieve decreased spider mite populations on peach leaves under any circumstances.

A large number of mite larvae feeding on aphids was observed between late June and early July, and between August and September in Shizuoka, Central Japan. Developmental times from egg to adult emergence at 15, 20, 25, and 30°C were 128.0, 67.5, 43.8, and 35.0 days, respectively; the lower threshold temperature and effective accumulative temperature for development were estimated as 9.3°C and 711 degree-days, respectively. The sexes were distinguishable by the presence of the amphioid sclerite that is positioned in the genital opening of the male. The sex ratio was approximately 1 : 1, and the body length of adult females was significantly larger than that of adult males.

To enable the use of the indigenous predator Scolothrips takahashii Priesner（Thysanoptera: Thripidae）for the control of spider mites（Acari: Tetranychidae）in integrated pest management（IPM）for strawberry cultivation, we conducted a laboratory screening of 26 pesticides. The mortality of the S. takahashii larvae that were treated with six pesticides（acetamiprid, nitenpyram, thiacloprid, pyridalyl, spinosad, and lufenuron）was 100% within 48 h of pesticide application. Two pesticides（pyridalyl and lufenuron）remained extremely effective up to 10 days after the pesticide treatment. In contrast, the remaining 20 pesticides had no significant influence on the survival of S. takahashii.

We constructed a new spraying system for acaricide susceptibility tests to replace the rotary distributing sprayer. The system consisted of an air compressor, airbrush and turntable. The tip of the airbrush was 30 cm above the laboratory table and was set 45 degrees downward. The distance between the tip of the airbrush and the center of the turntable was 28 cm, and the winding knob of the airbrush was loosened two turns from the tightly fastened state. Under this condition, the amount of water sprayed on filter paper on the turntable was closely correlated with the amount of water injected to the airbrush. The particle diameter size of the spray from the airbrush on the water sensitive paper on the turntable was smaller than that from the rotary distributing sprayer. The coefficient of variation of the diameter size of the spray from the airbrush was similar to that from the rotary distributing sprayer. Therefore, we expect this spraying system to replace the rotary distributing sprayer.