Effect of chlorpyrifos and methyl chlorpyrifos on controlling rice ieaffolder(Cnaphalocrocis medinalis Guenee)in field

Rice leaffolder(Cnaphalocrocis medinalis Guenee) hasbecome a serious pest on rice in Jiangsu Province. The in-sect appeared in Jul and remained until Sep. A field trialwith 5 treatments and three replications was laid out in arandomized complete block design in a farm field in Jiang-su, China in 1993. The hybrid rice tested was transplantedinto 2×25m plots. Using a knapsack sprayer, we applied

Toxicity of Bacillus thuringiensis Crystal Toxins to Field Populations of Rice Leaf Folder, Cnaphalocrocis medinalis （Guenee） and Establishment of Baseline Susceptibility to Cry1Ab

Eight insecticidal crystal proteins of Bacillus thuringiensis, CrylAa, CrylAb, CrylAc, CrylB, Cry2Aa, CrylC, CrylDa and Cry 1Ea were assessed for toxicity against 1 st instar larvae of rice leaf folder, Cnaphalocrocis medinalis （Guenee） at 48 HAT and 72 HAT. Bioassay results depicted CrylAa was the most toxic （LCso 2.35 ppm） followed by CrylBa （LCso 8,50 ppm） and CrylAb （LCso 8.73 ppm） at 48 HAT, whereas, at 72 HAT CrylAb proved to be highly toxic （LC50 0.50 ppm） followed by CrylAa （LCso 4.07 ppm）, CrylAc （LCso 4,84 ppm） and CrylBa （LCso 6.42 ppm）. Toxins Cry2Aa, CrylCa, CrylDa and CrylEa did not resulted in any mortality at 48 HAT and 72 HAT, respectively. Baseline estimates for CrylAb against 1st instar larvae of C. medinalis sampled from seven geographical locations revealed variation in LC50＇s from 0.37 ppm to LC50 16.25 ppm at 48 HAT and LC50 0.50 ppm to LC50 6.49 ppm 72 HAT, respectively with relative resistance ratios of 44-fold and 13-fold at 48 HAT and 72 HAT over the susceptible population.

Effect of Six-fourth Generation Cnaphalocrocis medinalis (Guenée) on Rice yield and Control Index

[Objective] The study aimed to find out effects of six-fourth generation Cnaphalocrocis medinalis （Guenée） on rice production in Yangzhou district and its control index. [Method] Through artificial control of insects in field, four different insect volume gradients were set, the effects of different C. medinalis amounts on leaf roll rate and yield loss of Wuyunjing No.23 were determined. [Result] The results showed that within the range of 0-20 head/hill, as the amounts of insect increased, rice yield decreased, leaf roll rate and rice yield loss rate increased. According to 3% economic permit loss rate, the control index of C. medinalis on Wuyunjing No.23 was 173 head/hill. [Conclusion] The study would provide theoretical basis for effective controlling of six-fourth generation C. medinalis in Yangzhou district.

Main Rice Pests Control with Trichogramma japonicum

This study used Trichogramma japonicumto to control Chilo suppressalis （Walker） and Cnaphalocrocis medinalis（Guenée）, and tested the effects of different control methods on main rice pests, natural enemies and rice yield. The results revealed that the parasitism of Trichogramma japonicum in the eggs of Chilo suppressalis （Walker） and Cnaphalocrocis medinalis （Guenée） reached 60.3% and 57.1%, and the control efficacy was up to 70.8 % and 91.99%, respectively. The control efficacy for Cnaphalocrocis medinalis （Guenée） was much better. This biological control method could be equivalent to chemical control method in the control effects on main pests in rice. The yield under the biological control was 26.5% higher than that of the control group, and the biological control had a signifcant increase in the number of natural enemies such as spider, up to 400 per 100 plants. Therefore, the sustainable prevention and control were achieved in the presentence with natural enemy organism.