| The pink stem borer. Sesamia inferens (Walker)(Lepidoptera:Noctuidae) and striped stem borer. Chilo suppressalis(Walker)(Lepidoptera:Pyralidae), are important pests on rice, especially in the southeastern provinces around the Yangtze River of striped stem borer, it causes dead hearts and whiteheads during the vegetative and reproductive stages respectively. S.inferens usually occurred at out part of paddy field and damaged less serious than C.suppressalis and Tryporyza incertulas (Walker), however, this pest has a broad range of host plants, and in recent years, with the changes in cultivation and diversification of crops, the damage caused by this insect becomes serious year by year, especially at the beginning of21th century, as reported in Anhui, Hubei, Hunan, Jiangsu and Jiangxi province. Chemical control has been a major measure to protect rice from damage by the pests, but with the development of insecticides resistance, many insecticides have lost the efficient control of the rice pests. So effect of general insecticides against the pests was assayed for efficient controlling strategy. Simultaneously, in order to master the insecticides resistance development, micro topical method were carried to survey the resistance of19populations of C.suppressalis from6provinces against5common insecticides which were frequently used in paddy field. The aim is to provide a rational guidance of insecticides application. Flubendiamide was developed by Nihon Nohyaku and showed efficient control on lepidopteran pests, it has been widely used since2010for C.suppressalis. In order to monitor the resistance change more better and supply the resitance management strategy earlier, susceptibility of strip stem borer to flubendiamide were assayed, and preliminary toxicity baseline of flubendiamide was established.Topical bioassay was carried out for sensibility of pink stem borer to4common insecticides, results showed that, the pests from different area showed significant discrimination of resistance, with susceptibility of population from Shanghai was lower than that from Jiangsu. Toxicitiy of4insecticides ordered as:abamectin) triazophos) monosultap>chlopyrifos, differed with their activity to striped stem borer, therefore, it was speculated that the common insecticides for control of rice stem borers in recent years was not conducive to the control of S. inferens. agent with high toxicity against this pest should be adopted for its control.Resistance bioassay results indicated that resistance level of rice stem borer populations from paddy varied among different regions, the higher resistant area located in Zhejiang, Anhui, Hubei and Jiangxi province, most of the colonies from Jiangsu and Sichuan province maintained susceptible. Field populations of Cangnan, Ruian, Xiangshan and Jinhua from Zhejiang province have developed high to extremely high level of resistance to triazophos (RR=58.1-555.5), moderate to high level of resistance to chlopyrifos (RR=29.8-133.6). low to moderate level of resistance to monosultap (RR-7.1-23.8). and decreased susceptibility to moderate level of resistance to abamectin (RR=3.4-11.2); Lujiang. Hexian. Guangde and Susong populations from Anhui province have developed moderate to high level of resistance to triazophos (RR=15.4-71.9), low to high level of resistance to chlopyrifos (RR=6.5-78.4), Susong population has developed moderate level of resistance to monosultap (RR=16.4), exclude this strain, the rest3populations of chilo suppressalis retained sensitive or decreased susceptibility to monosultap(RR=1.3-5.0); All the4populations have sensitive to low level of resistance to abamectin(RR=1.7-8.1); High level of resistance to triazophos were found in Wuxue population from Hubei province (RR=65.0) and it has developed moderate level of resistance to monosultap (RR=12.7) and low level of resistance to chlopyrifos and abamectin (RR=5.8and9.7); Besides, Xiaogan and Jinghzhou population from this province were of low to moderate level of resistance to triazophos (RR=9.8and18.4); Taihe population from Jiangxi province has developed extremely high level of resistance to triazophos (RR=201.4), moderate level of resistance to chlopyrifos and monosultap (RR=22.4and10.4), and low level of resistance to abamectin (RR=7.5), Shanggao population was low level of resistance to monosultap (RR=6.9) and moderate level of resistance to triazophos and chlopyrifos (RR=16.1and15.4); Jurong population from Jiangsu province has developed low level of resistance to triazophos (RR=6.9), and Yizheng population has developed low level of resistance to chlopyrifos and monosultap (RR=8.0and6.0). Excluding those strains, the other ones were still at susceptible or decreased susceptibility level to these4insecticides, thereafter, except for that Ruian and Cangnan population were of low level of resistance to emamectin, all of the other field populations remained sensitive or at the decreased susceptibility level.Flubendiamide is a novel class of insecticide acting on insect ryanodine receptors with efficient larvicidal against lepidopteran pests. In order to survey the initial evolution of resistance of stem borer to flubendiamide for prolonging the new pesticide life span, rice seedling dipping method was adopted in our study for susceptibility monitoring of C.suppressalis to flubendiamide,29different geographic field populations from7provinces were involved in this experiment and toxicity baseline of flubendiamide was established. The assay data indicated that the susceptibility of different population showed obvious variaty to this insecticide, the LC50values varied from0.032mg ai/L to1.090mg ai/L, among all the populations, FS11colony showed the highest susceptibility to this compound, simultaneously. JH12strain was the most tolerant one, and34.1times difference was detected between them, although obvious variation of susceptibility among different geographic populations were observed, no differences were found in most of the populations from the same location in different years except that LC50values of Jinhua population from Zhejiang province and Lujiang population from Anhui province in2012were significantly higher than that in2011. Population of Qianshan, Guangde from Anhui province; Fushun, Dazhu, Shuangliu, Renshou from Sichuan province and Duchang from Jiangxi province were the species which have never or seldom be exposd to flubendiamide, so they were considered as the sensitive ones and the data were pooled for establishing the baseline (LC50=0.092mg ai/L). Preliminary resistances were also assessed and the results indicated that Jinhua polulation has reached moderate level of resistance (RR=11.8-fold), besides, Cangnan, Xiangshan. Dong’an, Youxian, Zhongxiang. Wuxue, Duchang, Shanggao and Yizheng population were of low level of resistance (RR=5.1-9.0-fold), close observation should be put into action to master the dynamic state of flubendiamide resistance and conduct the rational use of this pesticide, accordingly, development of resistance will be delayed and the new type of these insecticides are protected. |
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