| Striped stem borer, Chilo suppressalis (Walker), is one of major insect pests of rice in China, especially in the valley of Changjiang River. In recent 10 years, population of this pest and its damage to rice increased dramatically, severely threatening the high and stable yields of rice. For a long time, populations of C. suppressalis are controlled mainly by the use of chemical insecticides. Insecticide resistance in C. suppressalis was one of the main factors for its infestation increase.Monosultap, triazophos, fipronil and abamectin are four major insecticides used to control C. suppressalis in recent years. They are different from each other in mode of action and with distinct application background in rice field. Zhejiang, Jiangsu, Anhui and Jiangxi are four provinces where infestation and damage of C. suppressalis are most serious. The aims of present study include: to investigate current situation of resistance in C. suppressalis to the above four insecticides in the four provinces; to estimate realized heritability of resistance against triazophos, monosultap and fipronil through selection so as to predict resistance development rate; to analyze mode of inheritance of triazophos and monosultap resistance by means of log dose-mortality probit line analysis; to determine cross resistance and susceptibility of selected resistant strains to various types of insecticides; and, to gain preliminary information on the possible underlying mechanism(s) of insecticide resistance in C. suppressalis.A field population (HLJ) was collected from Heilongjiang province, where little insecticide was used to control C. suppressalis before 1998, and used as reference susceptible strain for resistance determination. Baseline toxicities of 14 insecticides to 4th instar larvae of HLJ population were assayed using topical application method. The toxicity of these insecticides was in the order of abamectin > lambda-cyhalothrin, fipronil > phoxim,triazophos, chlorpyrifos, fenitrothion > tebufenozide > diazinon, methomyl, trichlorfon > endosulfan, monosultap, and acephate.During 2001-2003, insecticide resistance was determined with populations from four provinces-Zhejiang, Jiangsu, Anhui and Jiangxi. Results showed:(1) Fipronil. Fipronil is a more recently introduced insecticide for controlling of C. suppressalis and other rice pest insects in most places. But in Wenzhou and Taizhou area, southeast of Zhejiang province, it had been applied extensively to control heavy infestation of C. suppressalis since around 1997, two or three years earlier than other places and with more application times each year. Most populations examined remained susceptible (resistance ratios < 3-fold). However, in 2002, for the first time, a population (ZJRA) from Ruian, Zhejiang was found to have 8.7-fold resistance. The resistance was confirmed in the following year. In addition, populations from two adjacent counties --Pingyang (ZJPY) and Cangnan (ZJCN), to the south of Ruian, were also resistant to fipronil. Resistance ratios for these three populations in 2003 were 11.4- (ZJRA), 13.0- (ZJPY) and 15.0-fold (ZJCN).(2) Abamectin, an antibiotic with powerful insecticidal and miticidal action, had been used on rice to control C. suppressalis mainly in form of mixtures. Susceptibility to abamectin had not decreased significantly in any population detected (all resistance ratios < 3-fold).(3) Triazophos, an organophosphate, was first introduced to control monosultap-resistant C. suppressalis in early-1990s in Zhejiang. It has gradually replaced monosultap (and bisultap) becoming the preferred insecticide for controlling of C. suppressalis in large areas recent years. Resistance monitoring revealed that three populations ZJRA, ZJPY and ZJCN from Zhejiang had high or extremely high resistance; that ZJWZ population from Ouhai (a suburb district of Wenzhou, Zhejiang) had moderate resistance (18.2-fold); that four populations from Changshu (JSCS), Xishan (XS), Jintan (JSJT) and Wujin (WJ), all in south Jiangsu, had low level of resistance (6.0- to 9.7-f...
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