Determining Insecticde Susceptibility And Laboratory Screening For Combined Insecticide To Leaffolder, Cnaplocrocis Medinalis (Guenee) (Lepidoptera: Pyralidae)

The rice leaffolder, Cnaphalocrocis medinalis(Guenee) is one of the most important pests on rice crop in China. Chemical control is the major measure for suppression of Cnaphalocrocis medinalis (Lepidoptera:Pyralidae) damage. In recent years insecticides used for control of C. medinalis in China have been changed greatly. A few insecticides used for long time have been proved to fail to control this pest in China. Several new chemicals have been introduced for control of C. medinalis. However, there was litlle resistance data of C. medinalis to insecticides used or will-be in use. In this study, a seedling dipping method was developed for bioassay of insecticide susceptibility of C. medinalis, which choose C. medinalis one day-larvae as tested larvae and in which insecticide was spreaded by dipping seedling in working suspensions prepared by diluting the emulsifiable concentrates in water. This biossay method doesn't need complicated foodstuff and is suitable for screening pesticides and monitoring resistant on large scale. Furthermore, this method is also suitable for monitoring C. medinalis resistance to pesticides with stomach toxicity and contact toxicity.Dose responses of C. medinalis to 11 insecticides were tested. Inter-population sensitivity to insecticides was compared. Based on LC50 values, C. medinalis was most susceptible to antibiotic insecticides (abamectin, emamectin benzoate and spinosad), and least sensitive to monosultap and a Bt product. Chlorantraniliprole and insect growth regulator (IGR) insecticides (tebufenozide and hexaflumuron) showed great efficacy against C. medinalis. No susceptibility difference was observed for antibiotic insecticide and IGR insecticides among three populations. The LC50 values of C. medinalis are 0.006-0.009mg ai/L for abamectin,0.005-0.022mg AI/L for emamectin benzoate,0.008-0.016mg ai/L for spinosad,0.306-0.330mg AI/L for tebufenozide,and 0.131-0.218mg ai/L for hexeflumuron(data of two pupulations). Narrow variations in susceptibility were observed for organic phosphoric insecticies, chlorantranliprole, monosultap and Bt. Chlorpyriphos susceptibility of C. medinalis from Nanjing (LC50 value 1.584 mg/liter) was lower than those from Changsa (0.658 mg/liter) and Nanning (0.513 mg/liter). Quinalphos and triazophos susceptibility from Nanning were lower than those from Nanjing and Changsa. Chlorantraniliprole, Bt and monosultap susceptibility of C. medinalis from Changsa were higher than those from Nanning and Nanjing.The toxicity of combination with two components among abamectin, emamectin benzoate, tebufenozide, hexaflumuron, quinalphos and phoxim were assayed by seedling dipping method. Screen for two combinations with synergism effect from six combinations of 46 ratios in total. The CTC of A(1:99) and B(1:119) in combination#1 and E(1:9), F(1:11) and H(1:29) in combination#2 are 449 and 535,126,196 and 182, respectively. The results showed that these mixtures have synergism effect.Initial research on C. medinalis artificial diets was inclusived, which supply the basis for constant exploration.