Effects Of Landscape Composition And Pesticide Application On Natural Enemies And Their Aphid Biocontrol Services In Cotton Fields In Southern Xinjiang

Xinjiang is the largest cotton producing area and cotton yield accounts for more than 85% in China.The safe production of cotton in Xinjiang is related to the sustainable development of China's cotton industry.Although agricultural intensive management increases crop yields,it has also resulted in numerous problems such as reduction of non-crop habitats.The simplification of landscape patterns,might seriously destroying the balance between Plant-Enemies-Pests in the landscape pattern system,and may leading to frequent outbreaks of pests and overused pesticides.With the increasing comprehending of integrated pest management,ecological regulation has been extended from a single field ecosystem perspective to a regional landscape pattern.The view from single crop and single pest control in original perspective was extended to be associated with interaction among Crops-Enermies-Pests and Environment.Therefore,it is critically needed to understand the effect of landscape structure and pesticide application frequency on the pest and natural enemies.In this study,38 Bt cotton fields in Aksu prefecture were investigated systematically from 2018 to 2019.The pest and natural enemy population dynamic were investigated by visual observation.The information of pesticide applying frequency was investigated by questionnaire to farmers.The landscape structure within 2 km radius around the cotton field was investigated by field check.In addition,in order to clarify the effects of landscape structure and pesticide application on the abundance of predatory and parasitic natural enemies and its ability to control aphids in cotton field,the regression model among landscape variables,applying pesticide frequency,abundance of natural enemies population and two of parameters of bio-control in cotton field was established.The main results are following:The effect of landscape structure and pesticide use frequency on predatory enemies at three different growth periods of cotton analyzing results showing,1)during seedling stage of cotton,landscape diversity,which is depicted by Shannon Diversity Index,had positive correlation with ladybug abundance.There was a negative correlation between cotton habitats ratio and predators abundance.And other crops habitats(e.g.vegetable habitats,maize habitats,wheat habitats,etc.)ratio had negative correlation with predators and ladybugs abundance.Pesticides frequency had negative correlation with predators and ladybugs abundance.The ratio of predators to aphids in cotton field which is one of the parameters to measure bio-control,and it has a first tendency stage of increasing with landscape diversity and then reduction at second stage with landscape diversity promotion.Meanwhile,it was negatively correlated with pesticides frequency.2)In the cotton bud stage,landscape diversity and other crop habitats ratio were positively correlated with predators and ladybugs abundance,while cotton habitats proportion and pesticides frequency were negatively correlated with predators and ladybugs abundance.As for the ratio of predators to aphids,it was positive correlation between landscape diversity as well as other crops habitats ratio,but was negative with cotton habitats ratio and semi-habitats ratio.3)At boll stage of cotton,landscape diversity,other crop habitat proportion and cotton habitat proportion were negatively correlated with predators abundance and there was a negative correlation between other crops habitats ratio and ladybugs abundance.For the ratio of predators to aphids in cotton field,it was negatively correlated with landscape diversity,other crop habitats ratio and semi-habitats ratio.The effect of landscape structure and pesticide use frequency on parasitic enemies at three different growth periods of cotton analyzing results showing,1)at cotton seedling stage,there was a positive correlation between landscape diversity and mummified aphids abundance but a negative correlation between other crops habitats ratio and mummified aphids abundance.The parasitic rate,which is the ratio of mummified aphids abundance to the sum of mummified aphids and alive aphids abundance in cotton fields as one of parameter to measure the effect of bio-control from parasites enemies,had negative correlation with landscape diversity and cotton habitats ratio.2)In the stage of flowering bud,pesticides frequency was negatively correlated with mummified aphids abundance.Along with that,landscape diversity,cotton habitats proportion and pesticides frequency were negatively with parasitic rate,but there was a positive correlation between parasitic rate and other crop habitats proportion.3)During cotton boll stage,parasitism rate tend to increase at first and then decrease with landscape diversity increasing.However,there was a negatively correlation between other crop habitats proportion and parasitic rate but cotton habitats ratio was positively correlated with parasitic rate.