| The brown planthopper (BPH), Nilaparvata lugens (Stal), a migratory pest, is one of the most harmful pest in Asian rice production area. Negative effects can arise from abuse of chemical insecticide in farmland ecosystem and outbreak of BPH can also be attributed to some kinds of insecticides. It was found that emamectin benzoate, a new insecticide, could lead to the outbreak of BPH when applied to control and prevention of Lepidoptera pests in farmland in recent years, which increased the difficulty of controlling and prevention. Taking BPH and paddy filed spider as the object of study, this paper tested the toxicity of 6 commonly used insecticides such as emamectin benzoate and analyzed the influence of emamectin benzoate to eclosion and reproduction. It also studied the mechanism of emamectin benzoate working on BPH by simulate application in the field, which provided further theorical evidence to the control and prevention of BPH. The main results are as followed:1. The toxicity of six insecticides to three kinds of spiders.The toxicity of six insecticides to three kinds of spiders were tested in laboratory. The LC50 of emamectin benzoate to Lycosa pseudoamulata, Oedothorax insecticeps and Coleosoma octomaculatum of emamectin benzoate were 0.66mg/L,0.43mg/L and 0.45mg/L, respectively. The order of 24h toxicity to L. pseudoamulata was:Emamectin benzoate> Abamectin>Triazophos>Monosultap>Chlorpyrifos>Chlorantraniliprole; the order of 24h toxicity to O. insecticeps was:Emamectin benzoate>Triazophos>Abamectin>Chlorpyrifos >Monosultap>Chlorantraniliprole; the order of 24h toxicity to C. octomaculatum was: Emamectin benzoate> Abamectin> Chlorpyrifos> Triazophos> Monosultap> Chlorantraniliprole. The toxicity of emamectin benzoate was the highest to the three kinds of spiders. Test results showed that emamectin benzoate ranked the first place among the 6 commonly used insecticides and that the reduction of paddy field spider due to insecticides such as emamectin benzoate leaded to the resurgence of BPH.2. The effects of abamectin and emamectin benzoate on eclosion and fecundity of BPH.As a derivative of abamectin, the activity of emamectin benzoate is improved by 1 to 3 times. A simple method of rice seedling dip-molding was implemented to estimate the influence of emamectin benzoate and abamectin on BPH. It turned out that the toxicity of emamectin benzoate to BPH was greater than that of abamectin. Toxicities of the two chemicals on BPH were:LC50 of emamectin benzoate was 1.20mg/L and abamectin 2.03mg/L. The same method was applied to obtain the eclosion rate and reproductive rate of BPH under 4 dosages of each chemical, including LC15, LC30, LC50 and LC75. The results showed that when the BPH treated with emamectin benzoate, the eclosion rate was significantly lower than control and varied between 36.67%-80.67%; while the eclosion rate varied 34.67%-77.33%under the application of abamectin, which was significantly lower than control. Egg amount was used to represent the reproductive rate, and the reproductive rate was more complicated than eclosion rate. When the BPH was treated with 4 dosages of emamectin benzoate separately, the egg amounts were all significantly higher than control. Peak value of single gynogenesis was 454.8. The egg amounts of BPH under LC75 dosage of abamectin was at about 269.7 as much as the control. However, egg amounts of BPH under the other concentrations of abamectin showed significant differences with control, with the peak value of 423.4. It could be concluded that the eclosion rate and reproductive rate of the BPH were affected by emamectin benzoate and abamectin.3. The results of field application.Study was carried out the occurrence quantity of BPH in the field with different time and times of emamectin benzoate. The results showed that occurrence quantity of BPH was significantly higher than control area, especially the area in which emamectin benzoate was used for two times. The amounts of BPH were 9064.3 and 10031.6 in hundred cluster when emamectin benzoate was used for two times, and the amounts of BPH were 6976.9 and 6059.1 in hundred cluster when emamectin benzoate was used for one time. It was concluded that to use emamectin benzoate frequently would increase the occurrence trends of BPH.The amount of BPH was 5141.7 in one hundred cluster in the area where emamecti benzoate was applied for 3 times while amount was only 2487.0 in one hundred cluster if Chlorpyrifos was applied in the middle part. These three ways of applying emamectin benzoate can increase the occurrence quantity of BPH, and it were significantly higher than control. The above results showed that to keep on using emamectin benzoate in the early period could promote the resurgence of BPH. |
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