Effects Of Host Crop Composition And Climatic Factors On The Spatio-temporal Patterns Of Cotton Bollworm In Hubei Province

Helicoverpa armigera(Hübner),known as cotton bollworm(CBW),is a highly polyphagous agricultural pest that can cause damage to many economic and food crops,including cotton,corn,soybeans and peanuts.Benefitting from extensive planting of pest-resistant Bt cotton,the population density of CBW in China has been greatly reduced compared with that in the 1990 s.Consequently,the use of chemical pesticides has also been greatly decreased.With the decrease of chemical pesticide use,the influence of other factors on population control of CBW may gradually become more prominent.These factors include host composition,climatic factors,natural enemies and so on.But so far,the related researches,especially those on the regional scale are very scarce.In this study,the impact of some of these factors on CBW was investigated by data analysis.The data were collected from Hubei province,primarily in the cotton area of north Hubei and Jianghan Plain,which included the field population density of CBW,planting proportion of host crops,temperature and humidity in 14 sample sites during the years of 2008-2017.The main results are as follows:(1)Spatial and temporal differences of CBW population density in the field.Based on the analysis of the number of CBW eggs per 100 cotton plants in fields,it was found that the population density of CBW greatly fluctuated annually,but showed a decreasing trend.There was a significant spatial difference in the population density of CBW in the field,and the order of size of egg density at these 14 points was zaoyang,yicheng,wuxue,zhongxiang,jingzhou,zengdu,xiaogan,qianjiang,xiantao,xinzhou,zhijiang,gongan,tianmen and jianli.(2)Spatial and temporal differences in planting proportion and diversity of main host crops of CBW.The analysis based on the data of planting area of 7 main host crops of CBW showed that the planting area of 4 host crops including wheat,canola,cotton and vegetable at 14 points was relatively high.From 2008 to 2017,the proportion of cotton planting area decreased significantly,but the proportion of planted areas such as vegetables has increased significantly.The analysis of host crop diversity based on Simpson index and Shannon index showed that the annual change of host crop diversity was not significant,but there were significant spatial differences.Cluster analysis showed that the study area could be divided into four categories: the host crop diversity from low to high is north Hubei(G1),south central Hubei(G2),northeast Hubei(G3),and north central Hubei(G4).(3)Spatial and temporal changes of temperature and humidity.The temperature and humidity at the 14 points showed significant seasonal differences and annual fluctuations.The cluster analysis based on temperature showed that the study area could be divided into two major areas: northern Hubei and central Hubei(Jianghan Plain),and the temperature in northern Hubei is relatively low.The cluster analysis based on relative humidity showed that the study area could be classified into two subregions: northwestern Hubei and southeastern Hubei.The humidity in northwestern Hubei is relatively low.(4)The comprehensive influence of host crop composition and climate factors on population density of CBW.The impact of 10 factors as a whole on CBW eggs per 100 cotton plants was investigated by multivariate regression analysis.The 10 factors were the proportions of planting area of the 7 host crops(wheat,cotton,peanuts,beans,vegetables,corn,canola),Simpson index and annual average temperature,and annual average humidity.The results showed that the proportions of wheat,canola,corn,vegetables,the Simpson index,and the annual average temperature and annual average humidity had significant influence on the number of CBW eggs per 100 cotton in fields.The rest had no significant effects.Among the factors that had a significant effects,the proportions of canola and corn had a positive correlation with the number of CBW eggs per 100 cotton plants,while others a negative correlation with the number of CBW eggs per 100 cotton plants.In summary,there were significant spatial and temporal differences in CBW population density in the study area.This spatial and temporal difference was closely related to the planting proportion of several major host crops of CBW,the diversity of host crops,and the temperature and humidity.This study is helpful to understand the current status and distribution pattern of CBW in Hubei cotton area.The results lay the foundation for in-depth study of the influence mechanism of CBW and the comprehensive management of CBW in the future.