The Occurrence Characteristics And Causal Analysis Of Cnaphalocrocis Medinalis In Rice Paddies In Xing'an County, Guangxi

Rice is one of the important food crops in our land which is infected by many kinds of natural disasters,such as drought,flood and so on, all through the whole growth duration. But among these disasters,the severest one is the harm bringed by the "Two moved pests". They are one of the most serious disease of rice in China. At present,they become one of the dominating pests,which bring our rice paddies a bad harvest.Cnaphalocrocis medinalis (Guenee) is one of "two moved pests". It ranges large scope,migrates long distances, and has seasonal moved fly habits.Cnaphalocrocis medinalis is the primary pest on rice in Guangxi.It has 6～8 generations one year,and is one of the insect attacks which affected the largest area.It bringed great demage to rice production in Guangxi province,in recent years.Especially in 2008,it is the severest one throughout history. Guangxi is located in Southernmost Point of our mainland,and bounded by Vietnam.Which makes it become to the fist station of migration,and be called "bridgehead" and the source of breeding ground.Guangxi is the main route and the major breed place of migratory pests,and is also the main pest source place of the paddies in the middle and lower reaches of Changjiang River. So,it is so significant to research Cnaphalocrocis medinalis here,that we can establish the cure measures more easily and effectivly.During 2009 and 2010, we studied the occurrence rule of Cnaphalocrocis medialis in Guilin which is in northeast of China.The Altitude Seachlight trap,the Jiaduo automatic pest-detected light-trap and a systematic field investigation, matched with the pest female insect development level and the male and female ratio condition under the Altitude Seachlight trap and the weather dynamic change (temperature and humidity),gave us the conclusion what the population dynamics of the Cnaphalocrocis medialis occurs and its characteristics and causes.The results can give an early warning about the big happen of the Cnaphalocrocis medialis and provided the theory basis for effectively preventing and controlling the Cnaphalocrocis medialis.Cnaphalocrocis medinalis has 8 generations in Xing'an,Guangxi.The second generation(4/16～5/20) has a large number of them and smooth change.It is suitable for us to use the physical prevention and agricultural control to control them.The third generation(5/21～6/20)began to appear in late may,and had a large increase in June 8,because of the large number of immigration.It changed most frequently and also reached its top in this period of 2010.A number of Cnaphalocrocis medinalis immigrated here play the greatest part in the third generation. So,it is very important to contol its number in this period,with which we can cut off its later generations.In consideration of the large nunber,we should use the chemical control.The number of the foured generation remained stable until the third peak in late july,which occured in July 18 and 19. We should also use the chemical control to contol it.Afer late july,the rice came into its heading,flowering and filling period when its food condition deteriorated. So,the fifth generation (7/21～8/20) remained smoothly and stable all through this period.In this period,it should be effective to adopt the physical prevention and biological control expect the chemical control.The last three generations (9/21～12/10) remained a low number all the time,and can't do harm to rice,so we just needn't worry about it.The character cropping system of rice mixed planted in Guangxi is extremely beneficial to the continued occurrence of Cnaphalocrocis medialis.Cnaphalocrocis medialis infect the early rice firstly. When the early rice after heading, the comeum of the blade became harden and aren't suitable for larvae. Cnaphalocrocis medialis continue to infect the middle-season rice, so was the late rice. The period of infection can be extended, even several generations. According to this characteristic,we can take a series of measures such as installing fences between land in different period to reducing cross infection.