Resistance Monitoring To Insecticides And Exploration About Bioassay Method To Pymetrezine In Brown Planthopper, Nilaparvata Lugens (Stal)

The brown plant hopper (BPH), Nilaparvate lugens is one of the long-distance migratory insects in Asia. It is mainly found in the southern part, south-western part, middle and downstream areas of Yangtze River and Jianghuai area in China every year and has great impact on good quality and high production of rice in China. Due to the hysteretic nature of agricultural and biological control, chemical control is the main method to control brown plant hopper at present, but reports about resistance of brown plant hoppers to insecticides are continually growing due to widely use of the chemical insecticides. As a result, it is of great importance to know the resistance levels among different geographical populations to commonly used insecticides and to instruct reasonably the use of insecticides in field and resistance management.The research was aimed at knowing resistance levels of brown plant hoppers to different insecticides by monitoring resistance among different geographical populations. At the same time, a discussion about bioassay methods for pymetrezine towards brown plant hopper is also done in this paper in order to get a more accurate method to monitor resistance among field populations and to instruct use of insecticides in the field which could provide a theoretical basis of resistance management.1. Resistance monitoring to conventional insecticides in brown plant hopper.Resistance monitoring of brown plant hopper from different regions to insecticides was carried out in 2012 and 2013 by rice stem dipping method. The results are as followed:apart from the population from Guiling Guangxi remained low level resistance (6.9 fold) in 2012 to buprofezin, populations from Pudong Shanghai in 2012, Fuqing Fujian, Jurong Jiangsu and Hexian Anhui in 2013 reached extremely high level (176.0-247.5 fold), and other populations reached medium or high level resistance (23.6-156.8 fold); there was large difference in resistance level to pymetrezine among different populations over collecting time in 2012, and the resistance of Yongan Fujian population to pymetrezine which was the last to be collected reached 1167.7 fold, but the resistances of 4 populations which were collected earlier were at sensitivity decreasing to low level (4.0-7.3 fold). However, the populations in 2013 were all developed high to extremely high level of resistance (67.1-312.9 fold);results about monitoring to thiamethoxam indicated 32 brown plant hopper populations monitored in 2012 and 2013 were all medium or high level resistance (10.6-84.5 fold); different brown plant hopper populations were all susceptibility to nitenpyram (0.3-1.7 fold) and no significant difference was found between the years; resistances of brown plant hopper to organophosphorus pesticide, chlorpyrifos showed apart from the population from Nanning Guangxi where it was the first time to find high level resistance (74.8 fold) in 2012 and 2013, most populations were susceptibilitytolow level of resistance (1.4-8.7 fold);Thirty one brown plant hopper populations which were monitored in two years all showed extremely high level resistance to imidacloprid (170.1-1148.0 fold);susceptibility to low level of resistance (0.3-9.7 fold) to butene-fipronil in brown plant hopper.2. Discussion of Bioassay methods for pymetrezine.Pymetrezine had a good persistence bioactivity, but traditional method of rice stem dipping owing to a short dipping time may lead to a slightly high toxicity which might not be able to reflect the real toxicity. According to the special mechanism of pymetrezine, compare and discuss the methods of rice dipping, rice root dipping and the 5th method proposed by IRAC. The results showed methods of rice dipping is not suitable for the brown planthopper to toxicitymonitoring of Pymetrozine, the method of rice dipping has higher LC50 values under treatment of 192h, The result from IRAC NO.5 may be close to the real result.In a further study of IRAC NO.5, this method had a high requirement in insects’consistency; however, due to complexity of field environment and large individual difference in brown plant hopper this method is not suitable for resistance monitoring of field populations, but for the populations which have been fed in the laboratory for a period of time, the method can work in evaluation of efficacy in other similar pesticides because individual differences are supposed to decrease.