Background: The cultivation of Bt maize (maize genetically modified with Bacillus thuringiensis) continues to expand globally. Arbuscular mycorrhizal fungi (AMF), a kind of beneficially microbial community, closely related to soil fertility and plant nutrition, may influence the resistance risk of Bt crops against target lepidopteran pests.
Methods: In this study, transgenic Bt maize (Line IE09S034 with Cry1Ie vs. its parental line of non-Bt maize cv. Xianyu335) was inoculated with a species of AMF, Glomus caledonium (GC) and its outcomes on the food utilization, reproduction and development of armyworm, Mythimna separata were conducted in a potted experiment from 2017 to 2018.
Results: AMF inoculation showed favorable influence on the GC colonization of both modified and non-modified maize, and marked increase in the grain weight per plant and 1000-grain weight of modified and non-modified maize. Meanwhile, the cultivation of Bt maize didn’t significantly affected the AMF colonization. The feeding of M. separata with Bt maize resulted in a notable decrease in the parameters RCR, RGR, AD, ECI and ECD as compared with those observed in larvae fed with non-Bt maize in 2017 and 2018 regardless of GC inoculation. Furthermore, remarkable shortening of the adult longevity, remarkable prolongation of larval life span and remarkable decrease in the rate of pupation, weight of pupa, rate of eclosion and fecundity of M. separata was observed in Bt treatment regardless of GC inoculation during the two year experiment. Also, when M. separata was given Bt, a significant prolongation of larval life and shortening of the adult longevity, and a significant decrease of the pupal weight and fecundity of M. separate, was observed when inoculated with GC. However, it was just the opposite for larvae fed with non-Bt maize and inoculated with GC. The increased percentage of larval life-span, and the decrease percentages of the food utilization and the other indexes of reproduction, growth, and development of M. separata fed on Bt maize relative to non-Bt maize were all obviously lower under GC inoculation in contrast to the CK.
Discussion: It is presumed that Bt maize has marked adverse impact on the M. separata development, reproduction and feeding, especially in combination with the GC inoculation. And the GC inoculation favors the resistance efficiency of Bt maize against M. separata larvae through reducing their food utilization ability, and then negatively affecting the development and reproduction of the armyworm. So Bt maize inoculated with AMF (here, GC) can lessen the severe threats arising from armyworms, and hence the AMF inoculation may play important ecological functions in the field of Bt maize ecosystem with potentially high control efficiency for the target lepidopteran pests.