Effect of seasonal variation in host-plant quality on the rice leaf bug, Trigonotylus caelestialium

摘要

The rice leaf bug, Trigonotylus caelestialium (Kirkaldy) (Heteroptera: Miridae), is an important insect pest, causing pecky-rice damage in Japan. This bug has a multivoltine life cycle and feeds on various species of the Poaceae. The phenology of the host-plants differs between species and the plant quality of a single host species may change with the seasons. The fitness of the bug may be affected by these seasonal changes in host-plant quality. In the current study, the effects of such quality changes on adult and nymphal performance were examined using a population of bugs collected in Joetsu, Niigata, Japan. Rearing of newly emerged adults collected from spring to autumn from Italian rye grass, Lolium multiflorum Lam., and southern crabgrass, Digitaria ciliaris (Retz.), showed that body size and performance of adults differed between collection seasons and plant species, indicating that nymphal conditions including host-plant quality have crucial effects on their fitness. Rearing nymphs from hatching to adult emergence on various field-collected grasses under laboratory conditions showed that the performance of nymphs depends on the plant species and varies greatly with the season, within a given species. In general, nymphs performed more poorly on most of the plants collected late in the season, but they performed well on some plants unavailable early in the season. Therefore, in T. caelestialium, seasonal and spatial variations are important factors that affect fitness of nymphs and adults, and this suggests that oviposition of diapause eggs in summer is an adaptation to deteriorating food conditions.