Abstract:The rice leaf bug, Trigonotylus caelestialium (Kirkaldy), is a major species of stink bugs causing pecky rice. Seasonal prevalence of occurrence of this bug on rice plants in paddy fields was investigated by a sweeping method in Niigata Prefecture. The number of adult bugs captured by sweeping increased just after the rice plants reached the heading time, however it decreased quickly thereafter. The density of adults tended to be higher in an extremely early variety and an early variety of rice plant than a medium one. The number of males was more than the number of females, and the numbers fluctuated heavily. The nymphs appeared mainly from the middle to the end of the grain filling period. These nymphs originated from eggs laid by females which invaded the rice plants at the time of heading. The percentage of pecky rice grains tended to be high in the extremely early variety which showed a high hullcracked rice rate. Most of the pecky rice grains were damaged at the top or suture of the grains. Hull-cracked rice began to appear 10 days after heading time and increased to the maturing stage. Pecky rice grains began to appear 15 days after the heading time. Damage at the top part of the grains did not increase after maturation. On the other hand, grains damaged at the suture increased markedly up to maturing stage.
Abstract:The efficiency of a pheromone trap was evaluated as an alternative to the "sweeping method" that has been established as a monitoring method of the rice leaf bug, Trigonotylus caelestialium. A sticky trap, a plate with sticky surfaces on both sides, was used and a rubber septum impregnated with 0.01 mg of the synthetic sex pheromone was placed at the center of the upper side of the plate. The sticky traps were installed in paddy fields in Joetsu and Nagaoka, Niigata Prefecture and Toyama, Toyama Prefecture. The most effective trap height was estimated to be near the canopy of rice plants; therefore, the sticky trap was placed by poles at the height of the canopy in the center of a paddy field, and the traps were checked every day throughout the growing season in 2005. Monitoring by means of the sweeping method was also performed in the same fields at approximately five-day intervals. The number of adults captured by sweeping increased from the middle of June to early or mid-July, and then decreased, irrespective of region or rice variety, and the adults increased again at the heading time of each rice variety. The fluctuation pattern of males caught in traps and the number of males captured by sweeping were roughly synchronized in each paddy field. This result suggests that the pheromone trap can be utilized as a monitoring tool for the rice leaf bugs in paddy fields.
Abstract:The effects of supplying grains as supplementary food on nymphal development and the fecundity of adults in the rice leaf bug, Trigonotylus caelestialium (Kirkaldy), were investigated under laboratory conditions. The emergence rate of adults was 3.3% when nymphs were reared on rice seedlings alone, while the rate was 93.1-96.7% when nymphs were reared on rice seedlings with wheat grains or hulled rice. As compared with bugs reared on wheat seedlings alone, the developmental periods of nymphs reared on wheat seedlings with wheat grains or hulled rice were shorter, and the forewing length of the emerged adults was longer. The number of eggs produced by females fed on wheat seedlings with grains was 3.3-5.2-fold that of females fed on wheat seedlings alone. It was concluded that grains are very important food for the rice leaf bug, and that grain feeding raises its reproduction rate. It is suggested that the availability of seeds on the host plant affects the development and fecundity of this bug.
To develop new and improved pest management strategies against Trigonotylus caelestialium (Kirkaldy) (Heteroptera: Miridae), a major pest of rice in Japan, it is important to understand the mating behavior of this species. In this study, we examined the effect of mating on subsequent mating receptivity and longevity in female T. caelestialium. After mating, females temporarily exhibited decreased mating receptivity. In addition, the cumulative remating frequency of females that mated with a male that had just mated with another female was higher than that of females who mated with virgin males. As a result, we hypothesized that the male ejaculate reduces female mating receptivity. Furthermore, mated females survived longer without food and water than virgin females; on the other hand, the life span of mated females with access to food and water was less than that for virgin females.
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