Studies On The Population Dynamics Of Cotton Aphid (Aphis Gossypii) And Its Predatory Enemies In Organic Cotton Fields

In this dissertation, the population dynamics of cotton aphid(Aphis gossypii) and its predatory enemies were studied by systemic field investigation in the organic cotton field produce base in AkeSu city of XinJiang. The treatments included: (i) furrow irrigate organic cotton field(FOC); (ii)drip irrigate convertional cotton field(DCC); (iii) furrow irrigate convertional cotton field(FCC).The main results were as following: 1 The population dynamic of cotton aphid The whole investigation results show, the number of cotton aphid was FCC>DCC>FOC;The FOC aphid reduced its populations by 81% than DCC and 76% than FCC, respectively.The population peak of cotton aphid in two type conventional cotton field more earlier than in FOC,namely July 9 for convention cotton and July 14 for FOC;The number of the autumn aphid in FOC more fewer than in two convention cotton.The spatial distribution pattern of cotton aphid in all cotton field was aggregation. 2 The population dynamic and composition of predatory enemies The results indicated 28 species of predators belonging to 7 orders, 15 families, were found in coton fields. The natural population dynamics from various type of predatory enemies were different, Comparing the predator species of organic cotton fields with conventional cotton fields, Predator numbers in FOC were higher than in conventional cotton until late August when aphid populations in FOC declined. The number of predators in FOC is 2 times for FCC and 2.5 times for DCC, the predators population dynamic peak in two type conventional cotton field more earlier than organic cotton field,namely July 19 for conventional cotton and July 29 for FOC.The dominant predators were ladybirds and lacewings. 3 The characteristic of predatory enemies community The predatory enemies community in the three type of cotton fields were similar,although species abundant degree of predatory enemies community show:FOC>DCC>FCC,the diversity and evenness index of the predatory enemies community in FOC are lower than that in DCC and FCC,while dominant concentration index in FOC are higher than that in DDC and FCC.Index of diversity of predatory enemies community mainly depend on evenness index in three treatments.On the basis of the characteristics of the predatory enemies in different seasonal stage,we can divide the population dynamic into three stages. 4 The control of predators to cotton aphid The predatory enemies is considered to be crucial in preventing cotton aphid outbreak.The predatory enemies in FOC following cotton aphid better than in two type of conventional cotton field.Predatian pattern of predatory enemies on cotton aphid all belong to Holling's â…¡type;at the same time,the result by Grey relational grade analysis indicate the predatory enemies in FOC have better correlation with cotton aphid.