Effect Of Rice Leaffolder Cnaphalocrocis Medinalis Guenee And Brown Planthopper Nilaparvata Lugens St(?)l Infestations On The Uptake Function Of Rice Roots And The Resurgent Physiological Mechanism Of Nilaparvata Lugens

The rice leaffolder Cnaphalocrocis medinalis Guenee and the brown planthopper, Nilaparvata lugens (St?l) (Homoptera:Delphacidae), are important pests that impact rice development and grain quality. This paper investigated effect of C. medinalis and N. lugens infestations on the uptake function of rice roots and the resurgent physiological mechanism of N. lugens induced by insecticides. Results are as follows: 1. Changes of the uptake function of rice roots to nitrogen (N), phosphorus (P) and potassium (K) in a hydroponics culture solution were investigated in three experiments, namely: a single factor experiment involving C.medinalis larval infestation or simulated damages (cutting of leaves); paired combinations of two factors (leaf and root cuts); and combination of three factors (N. lugens infestation, and leaf and root removal). In the single-factor experiment, both C. medinalis feeding and leaf cutting significantly reduced the uptake of N by rice roots compared to the control. There were no significant differences in N concentration in hydroponics culture solution between treatments of one, two and four larvae per hill, but there were significant differences between two rates of leaf cutting. Also, C. medinalis larval feeding and the cutting of leaves reduced the uptake of P by roots significantly, but did not affect K uptake except when two thirds of the leaf area was removed. In the two-factor experiment, root removal promoted the uptake of N by roots and there was a significant interaction between leaf and root cutting treatments. In contrast, leaf and root removal significantly decreased the P uptake, but did not affect uptake of K. In the three-factor experiment, the effect by which cuts to the root system promoted the uptake of N by roots was counteracted by N. lugens infestation, and there were significant interactive effects on the uptake of N between N. lugens infestation, and the cuts in the leaf and root system. Also in the three-factor experiment N. lugens infestation and leaf cutting reduced significantly the uptake of P and K by roots. The removal of rice roots had no significant impact on the uptake of P and K.2. To understand the biochemical difference between immigrant and non-immigrant N. lugens offspring populations, we compared the changes in soluble sugar and crude fat contents in the 3rd and 5th instar nymphs and adult offspring from immigrant and non-immigrant N. lugens, and free amino acid content in immigrant adults and their offspring adults on two rice varieties (TN1 and Xieyou 963) under insecticides stress. The biochemical substances were associated with insect origin (immigrant or non-immigrant), developmental stages, and insecticide types and insecticide concentrations. Soluble sugar contents in the 3rd and 5th instar nymphs and adults offspring that developed from the plants treated with insecticides and control (untreated) plants of TN1 for immigrant N. lugens were significantly higher than those for non-immigrant N. lugens. In contrast to soluble sugar content, crude fat content in the 3rd and 5th instar nymphs and adults offspring that developed from the plants treated with insecticides and control plants of TN1 for immigrant N. lugens was significantly lower than that for non-immigrant N. lugens. For Xieyou 963, soluble sugar content in the 3rd and 5th instar nymphs showed the same tendency as TN1. Crude fat content in adults developed from control plants for immigrants was significantly higher than that for non-immigrant populations, and that in the 3rd and 5th instar nymphs did not show a significant difference between immigrant and non-immigrant N. lugens. Crude fat content in the 5th instar nymphs and adults which developed from the rice plants treated with insecticides for immigrant populations was significantly higher than that for non-immigrant. ANOVA results also demonstrated that as for changes in soluble sugar and crude fat contents, there were significant interactions between insect origin and insecticides, insect origin and insecticide concentration, and insecticide types and insecticide concentrations. For the two rice varieties, free amino acid content in immigrant adults was significantly lower than that in their offspring adults. Amino acid content in adults that developed from TN1 plants treated with triazophos was significantly higher than with deltamethrin and imidacloprid, while that in adults that developed from Xieyou 963 plants treated with deltamethrin and imidacloprid was significantly higher than that with triazophos. The present findings have important significance for understanding insecticide-induced resurgent mechanism of the migratory population of N. lugens.3. Changes of juvenile hormone(JH) and molting hormone (MH) levels in the 5th instar nymphs and adults were investigated under insecticides stress on two rice varieties (TN1 and Xieyou 963) .The level of hormone were associated with rice varieties (TN1 or Xieyou 963), application methods of insecticide and insecticide types and insecticide concentrations. For Xieyou 963, JH level in the 5th instar nymphs and adults following foliar spray before insect release was significantly higher than that following foliar spray after insect release, and also MH level in the adults following foliar spray before insect release was significantly higher than that following foliar spray after insect release. For TN1, JH and MH levels in the 5th instar nymphs and adults following foliar spray before insect release were significantly than those following foliar spray after insect release. ANOVA results also demonstrated that changes of JH and MH levels varied with time of foliar spray, insecticides and insecticide concentration. And also there were significant interactions between application time of insecticide and insecticide types, application time of insecticide and insecticide concentrations, insecticide types and insecticide concentrations. JH and MH levels in the 5th instar nymphs developed from TN1 plants treated with three insecticides was significantly higher than those developed from xieyou963 plants.4. Activity of protective enzymes and detoxifying enzymes in the 5th instar nymphs and adults were investigated under foliar spray of three insecticides on two rice varieties (TN1 and Xieyou 963). Activity of enzymes was associated with rice varieties (TN1 or Xieyou 963), application time of insecticide and insecticide types and insecticide concentrations. The activity of super oxide dismutase(SOD) in the 5th instar nymphs and adults developed from TN1 plants were significantly higher than that that developed from xieyou963 plants. The activity in the 5th instar nymphs and adults following foliar spray after insect release was significantly than that following foliar spray before insect release. The activity in the 5th instar nymphs and adults developed from rice plants treated with imidacloprid was significantly higher than that with triazophos. The activity of SOD in the 5th instar nymphs and adults on Xieyou963 and adults on TN1 were significantly higher than controls. The activity of peroxidase(POD) in the 5th instar nymphs and adults developed from TN1 plants were significantly higher than that that developed from Xieyou963 plants, that developed from rice plants treated with deltamethrin was significantly higher than with triazophos. The enzyme activity in N. lugens treated with low insecticide concentrations was significantly higher than controls. The activity of glutathione S-transferase(GST) in the 5th instar nymphs following foliar spray after insect release was significantly higher than that following foliar spray before insect release. GST activity in the 5th instar nymphs developed from feeding on TN1 and Xieyou 963 plants treated with deltamethrin was significantly higher than that with triazophos. For Xieyou 963, GST activity in the 5th instar nymphs following foliar spray with imidacloprid before insect release was significantly higher than that with deltamethrin and triazophos. GST in the 5 instar and adult on Xieyou 963 was significantly higher than controls. The activity of carboxylesterases(CaE) in the 5th instar nymphs and adults developed from TN1 plants were significantly higher than that developed from xieyou963 plants. The activity of CaE in the 5th instar nymphs and adults developed from TN1 treated with imidacloprid was significantly higher than with triazophos. The activity of CaE in the 5th instar nymphs developed from TN1 and xieyou963 were significantly higher than controls.