Effects Of Two Insecticides On Virus Transmission Ability Of Laodelphax Striatellus And Virulence Of RSV

Large-scale application of chemical pesticides has effectively controlled the serious outbreak of Laodelphax striatellus which spreads rice stripe virus in rice at the beginning of this century. Two pesticides with different mechanisms of action-imidacloprid and buprofezin which have been used widely in agricultural production, were chosen to study the effects of the two pesticides stress in rice seedlings on physiology and biochemistry of rice, the virus transmission of L. striatellus and RSV virulence. The toxicity of the two insecticides was tested with RSV-carrying and non-carrying L. striatellus population for the laboratory tests, and the honeydew excretion, carrier rate and capacity to spread virus of SBPH were detected, which were treated by different concentration of the insecticides and time. Rice plants infected for 48h by L. striatellus population with carrier rate of 92% were used for the outdoor test during the rice seedlings, and treated by imidacloprid and buprofezin once,2,3 and 4 times (Imidacloprid treatments were denoted by B1、B2、B3 and B4, and buprofezin treatments were S1, S2, S3 and S4, respectively) and no sprays as the control. Many indicators such as the physiological and biochemical characteristics of part rice plants, expressions of RSV various protein-coding RNA and SP protein periodically were tested. The honeydew excretion, the infection rate, and transmission ability of L. striatellus were determined after treated with different concentrations and at different time. The main results are as follows:1. The toxicity of the two insecticides was tested with infected and non-infected L. striatellus population, and the results showed that the toxicity tolerance of SBPH not infected population for the two insecticides was much higher than infected population striatellus. For the parameters of LC50, the toxicity tolerance of not infected population for imidacloprid was 20.84 times than infected population, and buprofezin was 11.94 times.2. The infected L. striatellus population were treated for 8h、12h and 24h with different concentration of the insecticides, then infected normal rice plants for 48h, and the CP and SP gene expression in rice plants were detected. The results showed that the CP genes expression of most treatments were prompted that during 8h-12h, and among these, four treatments of imidacloprid(20mg/L,30mg/L of 8h and 10mg/L,40mg/L of 12h) and one treatment of buprofezin (lOmg/L of 8h) were higher significantly than the control, others were not significant differences with control ultimately. After all treatment were treated by the two insecticides for 24h, the CP genes expression of these decreased significantly; The CP and SP gene expression showed the same change in trend, that is, during the short period the ability of spread virus of the infected SBPH treated by lower concentration of the two insecticides was improved, then declined.3. The honeydew secretion of SBPH (small brown planthopper) treated for 24h by imidacloprid and buprofezin was detected, and the results showed that the feeding activity of SBPH treated by lower than 30mg/L concentration of imidacloprid was stimulated, but inhibited when the concentration of imidacloprid was higher than 70mg/L or of buprofezin was higher than 20mg/L.4. The genes expression of NS2、NS3、NSvc2 and NSvc4 in rice plants was significantly affected, which the rice plants were treated by imidacloprid and buprofezin, and the difference of some was significant compared with the control. The genes expression of NS’2 in the rice plants treated by imidacloprid was inhibited or CK flat 16,19, and 21 days after inovulation. The NSvc2 and NS3 genes expression of B4 treatment were strongly induced 16 days after inovulation, and others were similar to or lower than CK. The NSvc4 genes expression of B1 and B4 treatments was strongly induced 16 days after inovulation, which levels were 103.65 and 229.12 times that of CK respectively, and others was inhibited significantly.24 days after inovulation, individual treatments of the four genes were induced to higher than CK. The genes expressions of NS2、 NS3、NSvc and NSvc4 in rice plants treated by buprofezin were regular, and the gene expression of NS2 and NS3 showed the same change in trend. That is,16 days after inovulation the gene expression of these were inhibited by all buprofezin treatments then increased, and S2 and S3 of NS2 was 188.64 and 144.17 times of CK respectively, NS3 was 71.64 and 67.81 times.19 days after inovulation, the genes expression of all treatments were different significantly with the control. The gene expression of NSvc2 and NSvc4 showed the same change in trend:the genes expression level of S2 and S3 treatments increased and was different with the CK 19 days after inovulation, S3, S4 and all treatments of the first sampling were CK flat.21 days after inovulation, the genes expression level of all treatments decreased, and were different from the CK, the level of NSvc2 and NSvc4 genes expression increased again ultimately, and S1, S2 and S4 of NSvc2 and all of NSvc4 were different over the same period control.5. The genes expression of CP (coat protein) and SP (special protein) was significantly affected by imidacloprid and buprofezin, and the expression of the two genes showed the same change in trend. Special performance was as follows:16 and 24 days after inovulation, CP genes expression was induced by B4 and B1, B4 treatments one after another. SP was induced by B1 and B4.19, and 21 days after inovulation, these two genes expression level of all treatments were the control flat or inhibited significantly.21 days after inovulation, CP and SP genes expression in rice plants treated by buprofezin was determinated, and the results suggested that the genes expression of other treatments was inhibited significantly, except that S2 was induced.24 days after inovulation, S3 and S4 didn’t change significantly.6. The expression levels of SP in rice plants were affected by the two insecticides. SP expression levels of all treatments were much lower than those of the control 16 days after inovulation, but 19,21 and 24 days after inovulation, those were induced and B2, B3 and B4 were similar to CK, and B1 was always higher than CK, whose peak was 507.36 times that of the control.16 days after inovulation, SP expression in rice plant treated with buprofezin was significantly upregulated except the two treatments, and S2, S3 and S4 treatments were 535.23,1503.98 and 1604.44 times that of the control respectively.21 and 24 days after inovulation, SP expression level of all treatments decreased and were 0～5.86 times of CK.