Fall armyworm (Spodoptera frugiperda) (J. E. Smith) (Lepidoptera: Noctuidae) infestation: maize yield depression and physiological basis of tolerance

Fall armyworm (Spodoptera frugiperda) (FAW) is an important invasive pest of maize. The young FAW larva disrupts the photosynthetic system by feeding on the leaves. The older caterpillar interferes with pollination and fertilization processes, destroying the tassel and silks, or it bores into the maize cob, reducing harvest quality and predisposing the cob to secondary infections. The infested plant responds by channeling or converting the primary metabolites into secondary metabolites for plant defense, further reducing crop yield. The devastating feeding effect on maize becomes even more severe when maize plants are exposed to prolonged drought, during which the production of secondary metabolites is optimum. These secondary metabolites are food for herbivorous insects like the fall armyworm. Naturally, plants possess several adaptive features which enable them to cope and survive herbivorous insect attacks without compensating yield for plant defense. Such features include: thickening of the leaf cuticle of the epidermal cell walls, production of certain allelochemicals, defense proteins and the toxic chemical compound, favone glycoside (silk maysin). This review attempts to critically appraise the physiological implications of fall armyworm damage on developmental processes and maize yield. Understanding the mechanisms of various adaptive traits that confer resistance to maize against herbivorous insect damage would assist greatly in crop improvement processes.