| The rice stem borer, Chilo suppressalis (Waker) is one of the most important rice pests and widely distributed in China. The extension of hybrid rice varieties, which are much favorable for this pest, results in continuous increase of the population density in recent decades. Applying chemicals has been a major means to control this pest. Since monosultap and methamidophos are the cheapest and most effective insecticides commonly used in China, farmers have mostly depended on them to control the rice stem borer. In 1980's and the middle of 1990's, only low or middle levels of insecticide resistance in rice stem borer were monitored. But with the population density increase and over application of monosultap and methamidophos, the resistance against them developed rapidly. Surprisingly high levels of resistance have been reported most recently in many areas of China, and even some control failures took place in Zhejiang and Jiangsu provinces, causing serious decrease in rice production and economic losses of farmers. However, little is known about the resistance mechanism. It becomes an urgent task to explore the resistance mechanism, and put forward rational resistance management tactics. In this study, the resistance situation was investigated, the biochemical mechanism involved was studied by measuring the detoxification enzyme activities, the cDNA encoding a subunit of nAChR the target for monosultap was cloned, and the cDNA polymorphisms were determined by comparing the cDNA sequences from susceptible and resistant individuals of Chilo suppressalis, the inhibition of monosultap against glutathione S-transferas (GSTs) was measured to reveal the synergism of cooperation of OP and nereistoxin, and the cDNA fragments encoding a subunit of nAChR from the diamond back moth , Plutella xylostella were cloned as well.The resistances of the rice stem borer, Chilo suppressalis (Walker) to monosultap and methamidophos were monitored in Cangnan, Cixi, Tonglu, Rui-an, and Wenglin in Zhejiang province, Changshu, Xuzhou, Gaochun, Funing, Jiangdu, Suyu, and Wuxian in Jiangsu province, and Guiyang in Guizhou province. The resistance dynamics withgenerations was investigated in a selected field population in Cixi city, Zhejiang province. The resistance stability was measured under insectary condition. The result showed all populations investigated in Zhejiang province had developed high resistance to monosultap except Wenling population holding 6.0-fold resistance. The resistance levels were as high as 95.8, 65.5 and 37.7-fold respectively in Ruian, Cangnan and Cixi populations. Chilo suppressalis had widely developed resistance against monosultap in Jiangsu province especially in Changshu, Gaochun, Xuzhou and Jiangdu, where Chilo suppressalis produced 126, 73.3, 68.5 and 33.2 fold resistance respectively against monosultap. Guiyang population was 9.6 fold resistant to monosultap. High resistance levels ranged from 33 to 143-fold against methamidophos were evolved in the monitored populations in Zhejiang province and Guiyang of Guizhou province, which were 143, 99, 85, 53, 34 and 33-fold respectively in Guiyang, Cangnan, Wenling, Cixi, Ruian and Tonglu populations. In Jiangsu province, resistance against methamidophos in monitored populations remained at middle level (under 30-fold) except Gaochun population holding 34 fold. The pattern of resistance dynamics differed between insecticides. To monosultap, the resistance level was as low as 37.7 fold in the 1st generation, increased rapidly in the 2nd and 3rd generation with the resistance of 47.4 and 94.6 fold respectively, and dropped to 47.5 fold in the 4th generation. The resistance to methamidophos and trichophon, however, appeared stable through the generations without much change. When the insecticide pressure was removed under insectary condition, the resistance of Chilo suppressalis against monosultap seemed stable in six generations without much fluctuation as in the field.The resistant population of the rice stem borer from Cixi, Zhejiang province... |
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