In southern paddy region, the larva density and eclosion rate are higher than previous year
The insect is becoming more resistant to paddy insecticide including chlorantraniliprole, chlorpyrifos, triazophos and abamectin;
China National Agricultural Technology Extension and Service Center (NATESC) recently warned of outbreaks of rice stem borer in southern paddy regions. Rice crops would be threatened due to the elevated insect population and resistance to insecticides including chlorantraniliprole, chlorpyrifos, triazophos and abamectin, etc.
Abnormal Larva Population
NATESC analyzed the field monitoring statistics and pointed out that the larva population in southern region is higher than in years past. Larva density in Jiangxi province was 803 larvae per hectare, up 165% from the previous year. Density in Hunan is 311.8 larvae per hectare, which almost doubled over the past year and is 1.5 times as much as the average density over the past 5 years. Density in Fujian and Zhejiang provinces were 248 and 188, increasing by 80% and 85.2% respectively. Only Hubei maintained a slightly lower density of 160, also above the threshold of outbreak potential.
The eclosion rate is significantly higher than the same period last year. Moth-trapping data shows that the number in Jiangxi province was 5 to 12 times as much as last year. 23 counties in Hunan trapped 3 times last year’s result. The emergence in Fujian and Zhejiang regions was also more severe than last year. Although these adult insects might not damage the crop directly, they can migrate to another region and their larval progeny would affect more area in the coming year.
Resistance to Insecticide Continue to Increase
In southern paddy region, insecticide resistance monitoring data reveals that the insect has developed varying degrees of resistance to common insecticides including chlorantraniliprole, chlorpyrifos, triazophos and abamectin. Hunan, Jiangxi, Zhejiang and Anhui have reported resistance to chlorantraniliprole and the regional resistance factor(RF) has grown from 16-70 in 2015 to 27.8-74 in 2016. The RF of chlorpyrifos in Hunan, Jiangxi, Zhejiang and Anhui has increased from 5.5-14 to 6.9-35 and RF of triazophos has increased from 7.7-80 to 8.8-87.1. The resistance to abamectin was most significant in south China. In 2014, only one region reported a RF of greater than 10 and the number of regions was 10 in 2015 and 12 in 2016, ranging from 52.9 to 94.1 in 5 counties from Hunan and Zhejiang.
Moderate to heavy rain is forecasted in southern China for the next 10 days, which will negatively impact both insect development and the application of pesticide. NATESC urged that all protection services should increase the monitoring frequency to contain the threat at its early stage.
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