Studies On The Occurrence Trend,Damage Loss And Control Threshold Of Corn Borer,ostrinia Furnacalis Guenée

The corn borer is one of the main pests of maize and other cereal crops in China.It is also an important and historic pest,which leads to huge economic losses to corn production.In this study,the resistance of different maize varieties to the corn borer,and its occurrence and damage were investigated.The control of the corn borer in Weibei area of Shaanxi Province was explored by Trichogramma dendrolimi.Further,the damage and loss of corn borer caused and its control threshold were studied systematically.The result provided a theoretical basis for scientifically manage and control of corn borer based on reducing pesticide application and increasing efficiency.The main results were as follows.1.There were significant differences in the resistance levels among the 27 maize varieties to corn borer.The highest and the lowest damage rate were 71.67%and 23.33%,aximum and minimum number of 100 plants were 20 or 80 insects per 100 plants,an average damage rate and average number were 45.74%and 51.94 insects per 100 plants,respectively.2.The control effect of T.dendrolimion on corn borer was poor.Our results showed that T.Dendrolimion has high control effect on stalk,up to 55～58%,but the effect on spike was merely 12%.The whole control effect was about 20%.The emergence of T.dendrolimion in laboratory and field indicated that emergence rate and emergence dynamics varied greatly.The emergence rate of paper board-T.dendrolimion was relatively high,up to approximately 70%,while perforated and plastic T.dendrolimion was only43.94%,which confirmed that perforated and plastic T.dendrolimion might affect the rate.The first batch of T.dendrolimion had the longest time,which up to 11 days and no obvious peak observed.The second and third batches of T.dendrolimion were 6 days,and the peaks were 2～3 days after emergence,respectively.3.In the study of damage loss and control threshold of corn borer,five maize varieties damage degree were significant differences in different years and varieties.These findings were consistent with the results of a wide range investigation on the resistance of various maize varieties to the corn borer.The average damage rate and number on every 100 maize plants of five maize varieties were 82.33%and 155.73 insects,respectively.The average damage rate and number on every 100 maize plants of ZY8911 were 69.33%and 115insects,respectively,which were significantly lower than that of the other four maize varieties in 2018.The average damage rate and average number on every 100 maize plants of five maize varieties was 15.9%and 19 insects.The average damage rate and average number on every 100 maize plants of SD650 were 22.5%and 28.50 insects in 2019.Compared to 2018,the damage degree was significantly lower in 2019.The main reason for this phenomenon is invasion of spodoptera frugiperda,which introduced into China at the first time in 2019.This was related to the insecticide spraying for 2 to 3 times in a large area to control spodoptera frugiperda.Meanwhile,it was a great killing effect on the corn borer in the middle growth of corn.Comparison of the degree of damage of different organizations,spike was obviously higher than stalk in the late growth stage of corn.The average spike damage rate of five maize varieties were 78.07%and 14.37%,respectively.The number of corn borers on every 100 spikes were 116.53 insects and 16 insects in 2018 and 2019,respectively.The average stalk damage rate of five maize varieties were 29.13%and 2.81%,the number of corn borers on every 100 stalks were 39.20 insects and 3.25 insects.4.The larval population density of corn borer in the field ranged from 0 to 4 insects per plant,and population density and yield loss rate was a positive correlation.Regression analysis showed that,the relationship between population density（X）and yield loss rate（Z）of five maizes in 2018 was as follows:Z_ZD958=1.367X﹣1.539,Z_SD609=2.059X﹣2.317,Z_SD650=2.139X﹣1.495,Z_XD47=1.908X﹣1.97,Z_ZY8911=1.309X﹣1.147;2019:Z_ZD958=1.2413X﹣1.0942,Z_SD609=1.8677X﹣1.7664,Z_SD650=1.6035X﹣1.6920.According to the analysis of investigation data about eight groups of five maize varieties in two years,and combined with the actual control cost of local corn borer,subsequently,the control threshold of the corn borer was 3.15 heads 1 plant.Consequently,there were significant differences in the resistance levels among the 27maize varieties to corn borers.Our study provided an important reference value in future production to select varieties with excellent resistance to pests and scientifically control the corn borer.The control effect of T.dendrolimion on borer needed to improve using further study.In accordance with the current situation of local maize production and combined with the actual control cost of local corn borer,its control threshold was 3.15 heads per plant.These results provide theoretical support for achieving zero increase of pesticide use in the control process of corn borer and promoting safety and efficiency of corn production.