| With the increasing of greenhouse vegetable areaes in Shandong province in recent years, vegetable production increased year by year. The prevention of vegetables from pests mainly depends on chemicals at present. Because of the use of chemical pesticides, the pest resistance became more serious and the pests were more difficult to control, and it also cause environmental pollution and pesticide residues, which seriously affect the quality of vegetables. To understand the occurrence of pests and their natural enemy insects in greenhouses of Shandong, study the effect of the natural enemy insect on controlling pests, screening pesticides which were safe for natural enemies and clear the influence of pesticides on the main natural enemy insect-Harmonia axyridis Pallas, this study investigated the occurrence regularity of pests and their natural enemy insects in tomato and cucumber greenhouses of Tai’an, Shandong,studied the effect of Encarsia formosa on controlling Bemisia tabaci, determined the sensitivity of Harmonia axyridis and Encarsia formosa to commonly used pesticides. In addition, the influence of3pesticides on dismutase (SOD), peroxidase (POD) and catalase (CAT) activity in Harmonia axyridis were also studied, to provide theory basis to the defense mechanism of Harmonia axyridis against insecticides.(1)The occurrence regularity of pests and their natural enemy insects in tomato and cucumber greenhouses: In Shandong Tai’an area, the main pests were Bemisia tabaci in tomato greenhouse, which occured in late April to early late June and September to early November. Cucumber greenhouse pests mainly were Trialeurodes vaporariorum, Bemisia tabaci and Thrips palmi, Trialeurodes vaporariorum and Bemisia tabaci occured in the middle of May to middle of July and late September to early November. The amount of Thrips palmi became very large in late May to mid-June and in early October to early November. The main natural enemy insects were Harmonia axyridis and Parasitoid wasp, which number were significantly lower than that in the open field vegetables.(2)The controlling effect of Encarsia formosa on whiteflies and the influence of isoprocarb on Encarsia formosa: The results indicated that after1d exposed to isoprocarb fumigant, the number of adults and nymphs of whiteflies declined significantly, mortalities rate were94.7%and76.0%. But the quantity of whiteflies increased rapidly again, this indicated that the effect of isoprocarb only lasted a few of days. After Encarsia formosa were released, the parasitic rate was rising slowly at the first one month, then rised rapidly with the increase of whiteflies, and reached the peak after2months, hereafter began to decline, with the population of whiteflies in low level. Isoprocarb fumigant was used after releaseing Encarsia formosa7d, the number of Encarsia formosa pupae declined77.6%, it showed that Encarsia formosa was very sensitive to isoprocarb.(3)Toxicity of commonly used pesticides to Encarsia formosa: Toxicity of6kinds of pesticides to adults of Encarsia formosa were assayed by using the pesticide-membrane method. The order from high to low was: abamectin> acetamiprid>imidacloprid> tebufenozide> pyridaben> buprofezin, the toxicity of abamectin and acetamiprid were the highest,whose toxicity indexes reached126.21and120.89, respectively, pyridaben and buprofezin were the lowest,the toxicity indexes were6.95and1.00.(4)The sensitivity of Harmonia axyridis Pallas to commonly used insecticides: this study respectively used dipping method and spraying method for the determination of7kinds of insecticides on eggs, the3-instar larvae and adults of Harmonia axyridis of virulence.Results showed that the toxicity of7kinds of pesticides to eggs decreased in this order: abamectin> imidacloprid> tebufenozide> acetamiprid>pyridaben> buprofezin> pymetrozine, whereas the sequence of toxicity to3instar larvae were abamectin> acetamiprid>imidacloprid> tebufenozide> pyridaben> buprofezin> pymetrozine, and the sequence of toxicity to adults were abamectin> acetamiprid>imidacloprid> pyridaben> tebufenozide> buprofezin> pymetrozine, and pymetrozine was the safest to Harmonia axyridis.(5)To study the effects of pesticides on the life activities of Harmonia axyridis and their defense mechanism, this experiment used nitroblue tetrazolium reduction method, guaiacol colorimetric method and UV spectrophotometry to determin the activities in Harmonia axyridis after treated with3kinds of pesticides.After respectively treated with abamectin, acetamiprid and imidacloprid of three sublethal dose concentration (LC10, LC20and LC30) for a certain time (12h,24h and48h), the protective enzyme activity in3instar larva and adult showed that LC10and LC20concentration of abamectin can promote the SOD and POD activity in larvae and adults, there is no obvious effect on CAT activity. LC30concentration can cause the inhitibion of3kinds of protective enzyme activity. Except the LC10concentrations of imidacloprid improved POD activity in larvae and adults, and CAT activity increased significantly in larvae and adults after12h treatments of three concentration, the remaining treatments showed inhibition on enzyme activity. LC10concentration of acetamiprid can promote SOD, POD and CAT activities in larvae and adults, LC30concentration can inhibited activity of3kinds of protective enzyme, after12h treatment of LC20concentration, the activity of protective enzyme increased at first, then declined and presented inhibitory effect. Overall, three kinds of enzyme activity decreased gradually as the growth of the treatment time, it suggested that pesticides at low doses had some negative effects on the life active of Harmonia axyridis Pallas. |
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