Effects Of Rewatering After Drought On Brown Planthopper Nilaparvata Lugens And Its Egg Parasitoid Anagrus Nilaparvatae

Brown planthopper (BPH), Nilaparvata lugens (Stal), is one of the major insect pests in rice production areas. Recent years, the outbreak of BPH increased with the changes of cultivation system, the popularization of high-yielding rice varieties, the improvement of fertilizer and water conditions, and the intensive and continuous use of chemical pesticides, and became a serious threat to rice production in China. Especially, BPH outbreak in southern China frequently, and caused massive crop losses since 2005. The occurrence of BPH was related with environmental conditions closely. Climate change in China is also very obvious together with the global climate changes. The frequency and intensity of drought have changed, with the regional drought worsening and drought areas increasing. This may affect BPH and its parasitoid natural enemy Anagrus nilaparvatae (Pang et Wang). This paper explored the impact of rewatering after different drought stress intensity and different duration simulated by Polyethylene Glycol (PEG) 6000 on changes of morphology and physiology of three rice varieties (TN1, susceptible; IR36, with resistant gene bph2; Huhan3, drought-tolerant), the ecological fitness of BPH and Anagrus nilaparvatae in laboratory. The main results are as follows:1. The height of rice plant decreased with increasing drought stress intensity, when drought stress after 7 days, height of three rice varieties was the lowest. Length and width of flag leaf, decreased with the increase of PEG 6000 concentrations. Diameter of rice stem decreased with the increased drought duration. Root length increased at first and then decreased with the increase concentrations of PEG6000. Root length Huhan3 was longer drought-stressed for 5 days than 3 days or 7 days. Root length of TN1 and IR36 were shortest when rice plants were drought-stressed by 20% PEG 6000 for 3 days. Relative water content (RWC) in leaves decreased with the increase PEG6000 concentration, and the decline degree of the RWC was greater on IR36 than on TN1 and Huhan3. The space and diameter of vascular bundles showed a decreased trend with the increased PEG6000 concentrations, and the changes were different on different varieties with the increase of drought duration. And it reached the lowest when it was drought-stressed by 20% PEG 6000 for 7 days on TN1, IR.36 and Huhan3, respectively.2. The nymphal duration of female BPH under the same conditions of drought stress was shortest at 28℃, and the nymphal duration of female BPH under 31℃ was between 25℃ and 28℃. Nymphal survival rate of BPH under 31℃ was lower than under 25℃ and 28℃. Weight and fecundity of female adult decreased with the increase of temperature between 25℃ to 31℃. Egg hatchability of BPH under 31℃ was significantly lower than under 25℃ and 28℃. The population growth rate of BPH under 31℃ was significantly lower than under 25℃ and 28℃. The interaction between high temperature and drought stress was shown on ecological fitness of BPH. Under the high temperature, the different intensity of drought led to the delation of nymph duration of BPH, reduction of nymphal survival rate, decreasion of adult weight fecundity and egg hatchability, which resulted in the reduction of BPH population growth rate. While under the same temperature, on TNI and IR36, the population of BPH drought-stressed for 7 days growed slower than that drought-stressed for 3 or 5 days. While on Huhan3, the population of BPH was reduced obviously when drought-stressed by 10%　PEG 6000 for 3 and 20%　for 7 days3. The developmental duration of　Anagrus nilaparvatae prolonged with the increase of drought stress intensity. Nymphal duration of A. nilaparvatae on IR36 was longer than on TN1 and Hunhan3 when drought-stressed by same concentration of PEG6000. The adult longevity decreased with the increase of drought intensity and it was shortest on TN1 and IR36 drought-stressed with 20%　PEG6000 for 7 days and on Huhan3 drought-stressed with 20%　PEG6000 for 5 days. Compared to those drought-stressed 20%　PEG 6000, A. nilaparvatae showed obvious selectivity to the control rice seedlings with BPH eggs on all three tested varieties. The amount of parasitoid BPH eggs on IR36 and Huhan3 drought-stressed by 20%　PEG6000 for 7 days was lowest. Parasitic capability of A. nilaparvatae on TN1 and Huhan3 was higher than on IR36.