This study was conducted to evaluate the attractiveness of the sex pheromone trap of Cnaphalocrocis medinalis Guenée as a forecasting tool from 2006 to 2008 in Suwon, Gyeong-gi province and Seosan, Chung-nam province, Korea. The sex pheromone lure was composed of Z11-18:Ald (55㎍): Z13-18:Ald (500㎍): Z11-18:OH (120㎍): Z13-18:OH (180㎍): Z13-18:Ac (55㎍) per a rubber septum, which set in a cylindrical cone trap. The trap catches of male moths was counted on a weekly basis and the lures were renewed every two weeks. The flight activity of C. medinalis moths monitored by the sex pheromone trap revealed two distinct peaks a year in both experimental areas from 2006 to 2008. Degree-days accumulation was calculated using lower developmental threshold (13.3℃) and degree-days (386.4DD) since adults had been first recorded. Estimated adult peak of the first generation was almost coincident with that observed by sex pheromone trap except in Suwon in 2008.

This study was carried out to determine the economic injury level of the rice leaffolder, Cnaphalocrocis medinalis G.. The damage aspects of rice plant (at tilling stage) by leaf folders at different larval density per plant were studied in pot experiment (24 ㎝ in diameter, 18 ㎝ in height). One leaf folder consumed 6-7 leaves during larval stage. The damage by leaf folders was simulated by cutting off 0, 10, 30, 50, 70, and 90% of leaves before and after heading stage July 15th (at panicle initiation stage) and August 15th (at milk stage), respectively. When leaves were cut before the heading of rice, the linear relationships between the leaf cutting rate (X) and each factors of yield (Y) were as following, for grain maturity it was Y = -9.379X + 83.630 (R² = 0.493), Y = 0.139X + 0.490 (R² = 0.925) for yield, and Y = -4.880X + 81.116 (R² = 0.665) for head rice. When leaves were cut after the beading of rice, it was Y = -23.014X + 83.589 (R² = 0.915) for grain maturity, Y = 0.141X + 3.466 (R² = 0.842) for yield, and Y = -13.795X + 81.964 (R² = 0.898) for head rice. We found that when leaf cutting after the heading stage caused more damage than before the heading in terms of yield and yield components. Based on theses results the economic threshold level was estimated to be 30% and 7% leaf loss before and after heading stage.

This paper reports a simple rearing system for Cnaphalocrocis medinalis based on com seedlings diet. C. medinalis population under this system has been maintained by four stages (egg, young larva-1st to 3rd instar, old larva-4th to prepupa, and adult) at 25±2℃, 40±10% RH, and 16L:8D photoperiod in a laboratory. We have elaborated a new egg collection method using a polystyrene container (top Ø11.3 × bottom Ø9 × H8㎝) which has made a great contribution in easy collection of eggs and storage of them for long period. Under this system, pupation and adult emergence rate and pupal weight of C. medinalis population were close to the other reports by corn seedling diet and superior to those by artificial diets. Therefore this rearing system would be useful in obtaining C. medinalsis population suitable to each specific needs.