| Corn(Zea mays L., Poaceae) is ranked first as food crop in planting area and in total yield production in China.. The problems caused by insect pests and diseases in corn appear to be increasing as cropping systems have been changed and the planting acreage have been increased in recent years, which result in very serious yield losses every year. Seed coating with pesticides has become the most economical method to protect corn from pest infestation. Most of the currently used seed coating with pesticides focus on the controlling of soil borne diseases and insects, and rarely on the control of insect pests in later stage of corn development. The objectives of this study were:(1) to estimate the effects of seed coating insecticides on corn seed germination, corn seedling growth and the control efficacy on thrips and beet armyworm Spodoptera exigua(Hübner) at seedling stage.(2) to evaluate the impacts of the seed coating insecticides on the corn seedling growth promoting and physiological and biochemical response by the determination of SOD activity, POD activity, CAT activity and total protein of corn leaves at four crucial developmental stages.(3) to evaluate the control efficacy of insect pests at corn whorl stage, ear stage and post-harvest stage, as well as the effects on regulated characters and yields of different treatments.(4) to detect residue of the 5 insecticides used in seed coating to evaluate the safety pesticide residues in corn grains of different treatments by seed coating. The main results are as follows:Treatments with 60% dinotefuran DP, 8%fipronil FS 70% thiamethoxam DP as well as 60% imidacloprid FS showed good promoting effects on seed germination, while some of the other treatments showed a negative effects. 70% thiamethoxam DP and 60% dinotefuran DP showed significant promoting on plant fresh weight, root fresh weight, plant height and number of leaves at seedling stage. Both of 70% thiamethoxam DP and 20% thiamethoxam CF had good control efficacy for thrips, and 20% thiamethoxam CF had the best control efficacy for beet armyworm at seedling stage among the 8 seed coating treaments.Each treatment has a promotion on SOD activity, POD activity, CAT activity and total protein at four stages to some extent. All of the enzyme activity and total protein increased gradually and reached the peak at the dough stage, then decreased. 20% thiamethoxam CF and 20% dinotefuran CF had a greater promotion on POD activity, CAT activity and total protein than other treatments at the first three stages.Control efficacy of Ostrinia furnacalis(Guenée)(Asian corn borer, ACB) in whorl leaf stage: 60% imidacloprid FS treatment showed no significant difference with the control on leaf feeding rates, but it had higher feeding rates than the control and had more numbers of ACB larvae per 100 plants significantly than that of control, in other words, treatment with 60% imidacloprid FS seed coting led to more serious damage by ACB. To the whole block control efficacy, treatments with insecticides had lower damage percentage than that of control. No significant effects were showed among different treatments on ear position and plant height. 8%fipronil FS treatments resulted in the highest yield among the treatments.Considering to the different recovery of 5 combinations of purification agents, we chose the combination of 40 mgPSA with 10 mgGCB to purify the samples. Results showed that residue of imidacloprid in corn kenerls was 3.69-4.22μg/kg, the residue of carbofuran and fipronil were 9.78μg/k and 0.83μg/kg, respectively, all of these three pesticide residue were much lower than the national standards. The thiamethoxam and dinotefuran residues in grains were 2.60-2.72μg/kg and 5.75-7.29μg/kg, we can’t tell whether the residue safe or not because there are no MRLs of both pesticides residue in corn grain set by our country. |
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