Pest status and loss assessment of crop damage caused by the rice borers, Chilo suppressalis and Tryporyza incertulas in China

This paper gives an overview on the history, pest status and damage assessment of the rice stem borer, Chilo suppressalis (Walker) and yellow rice borer, Tryporyza incertulas (Walker) in China. The first undoubted infestation and damage caused by these species was recorded in 1 022 during the Song Dynasty. The rice stem borer was dominant among these two species prior to 1956. However, the yellow rice borer increased significantly from 1956～1970. In the 1970's, the damage caused by these two borers was trifling. However, the population density of both pests had increased markedly by 1993 and outbreaks of both occurred in 1996. Since then, both species have caused disasterous crop damage every year. The present situation is characterized by a high density level, large area of infestation, severe crop damage, long time duration and huge economic loss. The most serious damage is found in the rice belt of Yangtze River Valley where about 2/3 of the damage is caused by the rice stem borer and 1/3 by the yellow rice borer. There is an estimated 15 million hectares per year infested with these pests and 38 million hectares that are treated with pesticides. We estimate that these pests cause a gross loss of 11.5 billion yuan (1 US dollar=8.27 yuan), consisting of 5 billion yuan control cost and 6.5 billion yuan of crop yield loss, each year. The authors believe that these two borers have become the No. 1 crop pests in China after the plant hoppers and cotton bollworm, Helicoverpa armigera (Hubner).