Studies On The Resistance Of Corn Vaireties To Pests And The Integrated Control Effects Of Pest Resistance Of Corn Vaireties With Natural Enemies On Pests

The resistance of corn varieties to insect pests and the integrated control effects of pest resistance of corn varieties with natural enemies on insect pests were studied based on the field experiments and systematic investigation. The main results were as follows:1Determination of the resistance of different corn varieties to insect pestsThe test results showed that among the tested33corn varieties, the resistance of different corn varieties to major insect pests had obvious difference, and the resistance to insect pests of the same variety in different growth periods also had obvious difference. Generally evaluating, the corn varieties of Xundan20, Ludan6018and Zhongke4had the best resistance to the major corn insect pests. Zhengdan958, Wanyu17, Zhengdan23and Nongda108had the medium resistance.Longping206, Zhongnongda236and Liyu35had the lowest resistance.2Effects of pest resistance of corn varieties on the arthropod community in corn fields2.1The species composition of the arthropod community in corn fieldsThere were23species of arthropods recorded in the field investigation. Among them, there were9species of pests,13species of natural enemies and one neutral species. The species richnesses were between8and15species in each investigation. In insect pests, there were6sucking species and the dominant species were Rhopalosiphum madis and Tetranychus cinnabarinus, and3chewing species of Potosia (Liocola) brevitarsis, Colapellus spp. and Ostrinia furnacalis. In predatory enemies, there were4species of spiders and9species of predatory insects. The dominant species of predatory enemies were Erigonidium graminicolum, Propylea japonica, Theridion octomacutatum and Orius similis and their number of individuals was about89%of that of predatory enemy community. The species and individuals of predatory enemies were rather rich, but the dominance of dominant species was significant.2.2Major characteristic indices and their dynamics of arthropod communities in corn fields of different varietiesThe different levels of pest resistance of the three corn varieties, Longping206, Nongdal08and Zhongke4had no evident effects on the species richness but had obvious effects on the evenness and diversity of arthropod community in corn fields. The peak periods of richness of arthropod community in the fields of the three corn varieties were in the big trumpet and the milk periods of corn growth. The evenness of arthropod communities in different corn variety fields had no evident difference before the first ten days of August, but presented obvious difference after the middle ten days of August because of the difference of population growth of Rhopalosiphum madis and Tetranychus truncatus in different corn varieties. The higher the level of pest resistance of corn variety, the higher the evenness of arthropod community in corn fields. The trend of diversity and evenness of arthropod community was similar.3Integrated control effects of pest resistance of corn varieties and natural enemiesThe level of pest resistance of corn varieties had evident effects on the ratio of natural enemies to pests. The ratio in the fields of corn varieties with relatively high level of pest resistance was higher than that in the fields of corn varieties with relatively low level of pest resistance. These results indicated that the pest resistance of corn varieties was helpful to increase the stability of arthropod community and the natural control effects of natural enemies on insect pests in corn fields.