Abstract: Field experiment results show that ACBs acquired Nosema furnacalis infection by vertical transmission were infected heavier than those by horizontal transmission. In the former case, borer population declined significantly at harvest time, but not in the latter case, though the incidence was as high as 91.5—95.5%. During overwintered period, the population of infected larvae declined. Sampling and examination of corn borers from overwintered cornstalks at three localities showed that the prevalence of Nosema was usually high, its increased mortality was more pronounced at prepupal stage. The paiasitism of larvae by Nosema and Beauveria bassiana resulted in obvious reduction in ACB population, but about 50% infected adults still emerged from the survivors as the new infectious source. Experimented result on the effect of ACBdensity on yield loss show that yield losses in the two of three test varieties were calculated as 1.32% and 1.39% for every additional borer respectively, but in the third variety, yield losses among different infected levels were not statistically significant. The variety showed a high tolerance to the ACB. The borer tolerant variety is advantageous to the circulation of infectious source and thus there is a coordinated relationship between microspridia and borer tolerant variety. It is suggested that borer tolerant varieties, microsporidia, together with other ecologioical factors, may compose a control system to reduce the ACBpopulation density to an economically tolerable level.

Key words: Nosema furnacalis, Ostrinia furnacalis, Borer tolerant variety, Coordinated relationship