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The rice stem borer (RSB), Chilo suppressalis Walker, one of the most important insect pests of rice distributes widely in China. With the changes in cropping system and global warming in recent years, occurrence and damage of RSB are on the increase. Elucidation of RSB female’s host recognition and resistance of rice varieties to RSB larvae, and their underlying mechanisms should shed light on new control measures for RSB population. In this thesis, preference of RSB females for different plants and resistance of rice varieties to RSB larvae were determined.1. Preference of RSB females for different plant speciesIn no-shield cage tests, oviposition by RSB females on different plants (rice, corn, wheat, ryegrass, cotton, cucumber, and leek) was investigated. RSB females preferred rice plants over corn plants, number of egg masses and eggs and egg hatching rate all being significantly higher on the former than on the latter; RSB females deposited no egg masses on other plants.The roles of visionary and olfactory cues in host recognition by RSB females were determined in olfaction-shielded and vision-shielded cage experiments, respectively. RSB females recognized plants via olfactory cues and vision cues were of little role.Preference to gramineous plants (rice, corn and wheat) and the roles of olfactory cues in host recognition by RSB females were further investigated using Y-tube olfactometer. RSB females preferred ordours from rice plants over those from corn and wheat plants, and showed no preference between corn and wheat plants. And, the females could not discriminate the ordours from intact rice plants, RSB larvae damaged rice plants and mechanically damaged rice plants.Oviposition preference of RSB females on three gramineous plants, rice, corn and wheat, was further determined in no-choice and choice cage tests. Under both conditions, RSB females significantly preferred to oviposit on rice plants, egg deposition and hatching rate on corn and wheat plants were significantly lower. The above experiments show that RSB females employs olfactory cues from plants to recognize host plants, vision is of little role; in olfactory recognition, green leaf volatiles overwhelm induced volatiles; and, RSB females show no preference for corn and wheat plants, indicating that corn and wheat are not host plants for RSB.2.Resistance of rice varieties to the stem borer and its underlying mechanismsTo screen resistant rice varieties in Liaohe Valley to the borer, development of and damage by the borer larvae on the varieties were examined using intact-plant resistance evaluation method, and morphological and biochemical characteristics and number of silica cells of the rice varieties were determined to explore the potential resistance mechanisms. Percent of damaged plant was the smallest on the variety Yanfeng 47, and larval weight on Shennong 265 was the lowest. Percent of damaged plant was found to be strongly correlated with angle of the reciprocal 2nd leaf and Si content in stem, where the former is a positive logarithmic correlation and the latter is a negative linear one. And, a strong positive linear correlation was revealed between larval weight and stem diameter.
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