Population Dynamics And Influencing Factors Of Coccinella Septempunctata And Harmonia Axyridis In The Wheat Fields

Global climate change has caused climate pattern changes in many regions of the world.Insects,as variable temperature animals,are bound to be affected by global climate change.Coccinella septempunctata and Harmonia axyridis are mainly predatory natural enemies in wheat fields,which play an important role in the prevention and control of pests in farmland ecosystem.Depending on the analysis of the two ladybird species occurrence data collected from wheat fields from 1991 to 2016,we found that the abundance of C.septempunctata showed a trend of decrease,while H.axyridis demonstrated a trend of increase.In this study,the reasons of the population change of C.septempunctata and H.axyridis in Shandong province were analyzed in three systematic plot,in the principle of distance of less than 70 km,Yanzhou in Jining,Longkou in Yantai and Taishan county in Tai'an was selected as three small wheat field system plot.Based on the decision tree algorithm,the classification model was constructed by using meteorological data,precipitation data and the occurrence data of ladybird in wheat field from 1991 to 2016.Furthermore,the principal component analysis of monthly average temperature and precipitation was made.The aim of this study was to provide a reasonable explanation for the dynamic changes of C.septempunctata and H.axyridis in wheat field in Shandong Province under the global climate change.1.Decision tree classification model was developed by using meteorological data and the use of pesticides with the occurrence of ladybird beetle for Jining,Yantai and Tai'an.It showed that a high correlation between the average temperature,the average relative humidity and the degree of pesticides with the occurrence rate of C.septempunctata in Jining,the sum of the information gain rate of 3 variables accounted for 87.76% of all variables.The average relative humidity,daily minimum temperature,and pesticides were related to the occurrence of H.axyridis,and the sum of the information gain rate accounts for 89.99%.In Yantai,pesticides,the average temperature and the average relative humidity were related to the occurrence of C.septempunctata,the sum of the information gain rate accounts for 90.43% of all variables.Pesticide,average temperature,and the minimum relative humidity most highly related to the occurrence of H.axyridis,the 3 variables of the information gain rate accounted for 89.34% of all variables.In Tai'an,The average temperature,average relative humidity,and pesticide were highly related to the occurrence of C.septempunctata,the information gain rate accounted for 93.08% of all variables,and the minimum relative humidity,average temperature,pesticides were related to the occurrence of H.axyridis,and the sum of the 3 variables accounted for 92.71% of all the variables.2.The correlation matrix of the average temperature,precipitation during the overwinter period of two species of ladybird beetles and the wheat growth period with the occurrence rate of two ladybird beetles in Jining,Yantai and Tai'an were studied.We find a positive correlation between the occurrence of ladybird beetles and the mean temperature and precipitation in overwinter period,and there was a negative correlation between the occurrence of C.septempunctata and mean temperature in May and June.For the H.axyridis,it was positively correlated with mean temperature in April and May,while correlated with precipitation in June negatively.Principal component analysis was conducted on the data of mean temperature and precipitation during the overwinter and the wheat growth period in Yanzhou,Longkou and Taishan county.By the principle of cumulative variance contribution rate is greater than 80%,two principal components are selected in each of the three plots.From the calculation of selected principal components in each variable,we could found that mean temperature and precipitation during overwinter period,mean temperature and precipitation in May and June accounted for a larger load in principal components are selected.3.Modeling the principal components by multiple linear regression,we obtained regression model for the occurrence of C.septempunctata and H.axyridis,the R2 value of all the models are within the interval [ 0.5,0.65),explanatory significatively,which could forecast the occurrence of the Ladybird beetles.In summary,the decision tree classification model and principal component analysis show that the average temperature,precipitation,organophosphorus pesticide are the mainly reasons of the population change of C.septempunctata and H.axyridis.