Storage of Stem Cuttings of Wheat Seedlings under High-Humidity Conditions to Improve Larval Emergence after Oviposition by Stenotus rubrovittatus (Matsumura) (Heteroptera: Miridae)

Successful rearing of Stenotus rubrovittatus, known to cause pecky rice, is complicated by the fact that adult females only oviposit into the spikelets of gramineous plants in nature. In this study, methods for rearing and collecting S. rubrovittatus nymphs using early wheat seedlings were investigated. Females were observed to oviposit their eggs into the coleoptile shortly after the appearance of the first foliage leaf from the coleoptile sheath (3 d after seeding). Nymph emergence from stem cuttings incubated on moist filter paper in a Petri dish was more than five times higher than it was from whole seedlings. Seventy two hours after oviposition, more than half of the eggs oviposited on the whole seedlings appeared on the outer surfaces of leaves following leaf elongation; these eggs did not hatch. The rate of emergence from eggs removed from the inner surfaces of leaves and incubated in Petri dishes was 86.7% at a relative humidity (RH) of 100%, decreasing markedly when RH <= 97%. These findings implied that eggs which became exposed outside the sheaths would not hatch due to desiccation. Conversely, egg-feeding by adults was not considered to have a negative effect on the hatching rates of exposed eggs. However, when the duration of seedling exposure increased, egg-feeding by adults resulted in increased egg losses. In addition, an overall increase in adult densities resulted in a decrease in nymphal emergence per female. Consequently, the number of hatching nymphs could be increased by storing the stem cuttings of wheat seedlings on moist filter paper in Petri dishes following adult oviposition, ensuring that the densities of adults were maintained at the optimal level of 30 pairs of males and females per 100 seedlings, and by replacing wheat seedlings at 24 h intervals.