Studies on the Population Dynamic and Optimal Control Time of Rice Leaf Roller
1. The rice leaf roller (Cnaphalocrocis medinalis Guenee) has become one of the main insect pests on rice in Chia-Nan area recently. And 18~24% of yield loss was caused by the pest in second rice crop.
2. Different area prepared the different population density. Where Tseng-Wen, Hsing-Ing, Chia-Yi, Fu-Wei and Tou-Liu prepared the highest population. The population of pests in the costal area of this island, such as Pei-Men, Tong-Shih and Pei-Kang etc, generally was lower than other area.
3. The annual population fluctuation was varied in different area. According to the 11-area investigation in Tainan District, the population dynamic was divided into 3 types.
A. Early type: The pest occurred and attacked in both the first rice crop and the second rice crop but it caused much more serious damage in the second rice crop than in the first rice crop. The area included Tseng-Wen, Hsing-Ing, Chia-Yi, Tou-Liu and Fu-Wei, etc.
B. Late type: The pest occurred mainly in second rice crop and caused more damage. The area included Hsing-Fung, Hsing-Hwa, Chung-Pu, Tong-Shih and Pei-Kang, etc.
C. Medium type: The pest mainly attacked on the inter mediate crop of rice. The occurring season was from late June to mid October. The area included Pei-Men and Tainan city.
4. It caused 1.5~1.7, 2.8~3.7, 4.9~6.6 and 9~15.7% of yield loss when the pest rolled 2%, 5% and 15% leaves, respectively.
5.It is much more economic to control the pest at the time 2% of leaves rolled by the pest, and 5% of leaves rolled comes to the next. But it must be rapid more attention to the right time for control.