Preliminary Resistance Identification Of Corn Varieties And Their Influence To The Population Growth Of Rhopalosiphum Maidis Fitch (Homoptera:Aphididae)

It is an important approach of control aphids damage to make use of cropresistance. The corn aphid, Rhopalosiphum maidis, is one of the major pests infesting thecorn. In this dissertation, four kinds of maize cultivars in Henan province and seven inbredlines of maize with different aphid-resistance were used to study the occurring regulationand the distribution of corn aphid and its natural enemies in Zhumadian and Zhengzhou city,Henan Province, and explore the feasibility using aphid index as the standard foraphid-resistance evaluation of corns. Further more, the electrical penetration graph wereapplied to analyse the feeding behavior on Bt and non-Bt corn hybrids, expecting to providereference index for aphid resistance identification of maize varieties and theoretical basis forthe corn breeding of aphid-resistance as well as the aphid comprehensive management. Themain results obtained in this study are as follows:Population fluctuation of corn aphid in field: By surveying the number of corn aphidpopulations on the entire maize growing period, the results show that corn aphid moved intothe corn field in mid-July, the number of increasing peak period of the aphid is frommid-August to early September, the aphid moves out of the field in late September,indicating the suitable growing season for the aphid is from corn tasseling to filling period.The survey of corn aphid population density shows the difference during the amount ofmaize varieties (lines) with different aphid-resistance.Aphid-resistance of different corn varieties (lines): The aphid-resistance of11cornvarieties (lines) were evaluated using aphid index. The results indicated that “Xundan20”and “Zhengdan958” showed highest rasistance level,“Liangyu88” and “Xianyu335” atresistant level. Among the seven inbred lines, the level of “Chang7” and “Chang7-2” wereat high resistance level and resistance level, respectively, with “Qi319” at high susceptibilitylevel. Among the seven inbred lines, the level of “Chang7” and “Chang7-2” were at highresistance level and resistance level, respectively, with “Qi319” at high susceptibilitylevel.We established a method that using the aphid index from tasseling stage to grain filling stage represented the aphid index during whole growth period, and the results showed thatthe conclusion of identification in Zhumadian and Zhengzhou was consistent, indicating thatthe aphid index method was feasible.Vertical distribution of corn aphids in corn plants: Corn aphid made serious damageduring corn tasseling and filling period，we can use the number of aphids on tasseling andcornears as measurable indicators on the whole plant. The main function of the alatae ismigrating towards the suitable environment.The population fluctuation about main natural enemies of corn aphid: the naturalenemies of corn aphid are rich in species numbers, but common natural enemies on field arerelatively single, mainly as lady beetle and spiders. The mixed population of lady beetles andspiders were investigated, respectively. The population growth and decline trends showedthat the lady beetles were the specificity predators of corn aphid, but the spiders were theeuryphagous predators of corn aphid. The results may be helpful to biological control of cornaphids.Feeding behavior of corn aphid on different maize cultivars: The EPG results show thatthe corn aphid feed on the susceptible varieties of maize easily, in contrast with aphidresistance maize varieties, which suggested there must be some factors disturbing aphidfeeding in aphid resistance varieties, confirmed by the results of the identification of aphidresistance in field meanwhile.Comparing the EPG parameters of the aphid feedind on Bt and non-Bt maizes, we findtransgenic Bt corn varieties are influential for non-target pests, although no direct effect, butstill have obstacles by feeding on aphids, but this effect is not obvious. It is not sure that Btcorn has the chemicals changed or the diversification about physical properties of the surface,it is worth to further study on the impact of these changes on non-target pests.