A Study On Population Dynamics Of Cereal Aphids And The Critical Time For Controlling The Cereal Aphids In Zoucheng

Cereal aphid is the most important pests in Zoucheng. To develop the pesticide reduction technology forcontrolling cereal aphid, a preliminary study was conducted to reveral the effects of one-time chemicalcontrol on population dynamics of cereal aphid and their natural enemies and wheat yield. Through thetwo-year investigation in Zoucheng, Shandong Province, we found that the peak density for cereal aphidwas between the periods of ES61to ES75during early flowering to milk stage. The peak of mixedpopulation of cereal aphid, i.e.1st-3rd instar nymphs,4th instar nymphs, winged and wingless adultaphid population was consistent with the wheat growing period ES69to ES75period, and the aphidRhopalosiphum padi was the dominant species, followed by Sitobion avenae, while Schizaphisgraminum was less occuerred. In2011, the amount of aphids per100tillers in was over3000ES69period, of which83%was the1st-3rd instar nymphs, and the4th instar winged aphids and winglessadult aphid was9%and7%, respectively. The winged4th instar nymphs and winged adult aphids wererelatively small. Of the mixed aphid population, nearly a quarter (24%) aphids distributed on spike, andfollowed by the2nd and3rd distributed on leaves (24%and21%, respectively). Cereal aphidsdistributed in the upper part of the wheat plants were the most, whereas in the lower part of wasrelatively small. In2010and2011, peak density of population dynamics for natural enemies was in theperiod of ES75-ES81. The cereal aphid population peaked at wheat growing season when averagetemperature was around25℃. With the average daily temperature is maintained at about25℃or evenhigher, the population density of cereal aphids declined sharply. Prevention and control of wheat aphidpopulations at least from the perspective of control wheat aphid population alone, the effect of sprayingduring this period the best in a one-time spraying of wheat semi-heading stage. Overall, flowering late(ES69) spraying the highest yield of wheat. Therefore, flowering late one-time spraying the measures ofprevention and control of wheat aphid is most favorable to increase wheat production. Without sprayingpesticide in the milk stage, resulting in wheat was significantly cut. Solely from the point of view ofcontrol wheat aphid populations, wheat heading stage (ES55) spraying of the best. In this period,however, spraying, impact of predatory enemies of the lacewings, ladybugs, hover flies and parasiticwasps and other parasitic natural enemies of insect. Lacewings, ladybirds and other predatory enemiesare polyphagous insects, of these natural enemies of insects a significant reduction in the incidence ofother pests may have a certain impact and development. In the one-time spraying of wheat floweringlate (ES69), wheat grain weight, instead of spraying, spraying too early (at jointing and flowering early)or late (milk stage), and both can cause wheat significantly cut. Therefore, one-time spraying to controlwheat aphids during the late flowering period is to be the best result. This study provides the basis forthe reduction of pesticides control of cereal aphids.