Effect of irrigation method on population dynamics of Nilaparvata lugens and natural enemies of high-quality late rice field

High-quality late rice is preferred by most consumers for its good taste. Irrigation is an important management practice in rice cultivation. This study analyzed the effects of irrigation method on the population dynamics of Nilaparvata lugens (St?l) and the main natural enemies Cyrtorrhinus livdipennis (Reute), Pardosa pseudoannulata (Bose. et Str., l906) of high-quality late rice. The study also determined the effective irrigation method which reduced the occurrence of N. lugens , that in turn reduced the use of chemical pesticides, and improved rice quality and cultivation efficiency. To do so, deficit irrigation, wet irrigation, intermittent irrigation and long-term irrigation were set up to study the effects of the various irrigation methods on the population dynamics of N. lugens and the main natural enemies of high-quality late rice under two pest control methods (biological and chemical control) and two isolation methods (semi-partitioning and full-partitioning method). The results showed that C. livdipennis occurred after N. lugens , which limited the effective control of N. lugens by C. livdipennis . The population of N. lugens under long-term irrigation was less than that under deficit irrigation and P. pseudoannulata under deficit irrigation was less than that under other irrigation methods. These differences were significant for main growth stages (booting stage to milk stage) when there was rapid growth of late rice brown plant hopper under biological control. There were significant correlations of population changes between P. pseudoannulata and C. livdipennis and N. lugens. P. pseudoannulata had an absolute control over N. lugens when N. lugens population was less than 1 891.1 per 100-clump and the ratio of N. lugens to P. pseudoannulata exceeded 9.67. Chemical pesticides had a severe lethal effect on C. livdipennis under all the irrigation methods. Long-term irrigation greatly reduced the toxicity of chemical pesticides to P. pseudoannulata . In summary, long-term irrigation was beneficial for the protection of main natural enemies of paddy rice and it was the best prevention option for N. lugens . Long-term irrigation combined production with water saving, explored the use of sub-long-term irrigation in the growth period of late rice and thereby enhanced effective water saving and reduced use of chemical pesticides.