Studies On Resistance And Ozone Water Control Of Bradysia Odoriphaga

Bradysia odoriphaga Yang et Zhang is an important underground pest threatening some kinds of vegetables in north China, which belongs to Diptera Sciaridae. It is difficult to control for its small body, high reproducibility and serious generation overlapping. In order to control this insect pest, dosage of pesticides was increased which causing pesticide residue and pesticide resistance. As food safety issues attracted more attention, non-toxic and no pollution pesticides were needed to control B. odoriphaga effectively. Moreover, B. odoriphaga is a kind of minor crops pest, the limited type of common pesticides led to pesticide resistance easilier.In this experiment, the levels of resistance to seven commonly used insecticides in eight populations of B. odoriphaga collected from Shandong Province were evaluated, and their resistance mechanism was studied. Meanwhile, the effect of ozone water and ozone water-insecticide combination on B. odoriphaga were detected. This research aimed to take targeted measures, alleviate pesticide resistance and reduce the usage of pesticide, which can provide theoretical basis for B. odoriphaga control. The main results are as follows:1. In order to determine the pesticide toxicity, we detected 10 different types of insecticides on 3th instar larvae of B. odoriphaga. Stomach-contact combination toxicity method was adopted. The results showed, the order of toxicity of 7 insecticides to B.odoriphaga was clothianidin > imidacloprid > thiamethoxam > lambda-cyhalothrin > phoxim > eta-cypermethrin > chlorpyrifos(after 48 h). While toxicity of doramectin, tefluthrin and matrine are relatively low, LC50 was 58.982 mg /L、61.698 mg /L and 76.865 mg /L, respectively.2. It was evaluated the levels of resistance to seven commonly used insecticides: chlorpyrifos, phoxim, beta-cypermethrin, lambda-cyhalothrin, imidacloprid, thiamethoxamin and clothianidinin seven populations of B. odoriphaga collected from Shandong Province. Stomach-contact combination toxicity method was adopted. We can see that B. odoriphaga populations exhibited common resistance to chlorpyrifos and phoxim, especially the resistance ratio of Shenxian population was more than 30-fold to chlorpyrifos. Shenxian population showed moderate resistance to eta-cypermethrin, while Tai’an population had low level resistance to eta-cypermethrin and lambda-cyhalothrin. However, all tested populations were relatively sensitive to imidacloprid, thiamethoxam and clothianidin.3. To investigate the relationship between insecticide resistance and activities of acetylcholinesterase, glutathione S-transferase, carboxylesterase and ODM, the activities of ACh E, GSTs, Car E and ODM in different field populations of B. odoriphaga were measured by spectrophotometry. The results showed that the activities of ACh E, GSTs and ODM in the B.odoriphaga from Tai’an, Shenxian, Shouguang and Linshu were significantly higher than those in the relatively sensitive strain, with relative ratios of 1.43-2.27, 1.24-3.07 and 1.28-2.61, respectively(P<0.05).There was a positive correlation between GSTs, ACh E and ODM activities and the insecticide resistance. On the other hand, there were no significant differences in Car E activity between most of the field populations and the relatively sensitive strain, with a relative ratio of 1.02-1.20. Therefore, ACh E, GSTs and ODM are closely related to the development of insecticide resistance in B. odoriphaga.4. With elevation of ozone water concentration(from 2 mg/L to 10 mg/L)., there was a gradual increase in % corrected mortality reaching. At concentration of 10 mg/L, ozone water proved highly toxicity against B. odoriphaga with corrected mortality exceeding 80.00%. What’s more, decrease in corrected mortality of tested insects with rise of temperature of ozone water(4 mg/L). The corrected mortality were 79.32% when ozone water at temperature of 12℃. While at temperature of 24℃,the corrected mortality of 3th instar larvae was as low as 20.00%.5. Field experiment showed that the control efficacy after seven, fourteen, twenty-one, twenty-eight, thirty-five and forty-two days of treatment at 9 mg/L concentration ozone water was 69.25%, 55.32%, 68.09%, 66.25%, 71.33% and 70.37%, respectively. Ozone water at the largest tested concentration of 9 mg/L exhibits good affect for B.odoriphaga control.6. The LC50 value caused by ozone water(4 mg/L)-insecticide combination was lower than that of insecticide alone, to clothianidin, imidacloprid, thiamethoxam, eta-cypermethrin and chlorpyrifos, the ratio of them was 0.54, 0.69, 0.42, 0.41, 0.48, 0.26 and 0.34, respectively. The study indicated that ozone water-insecticide combination may reduce the insecticide.