Incidence and damage caused by maize stemborers on farmers' fields in south western nigeria

The incidence and damage of maize (Zea mays L.) by stemborers complex of Eldana saccharina Walker, Sesamia calamistis Hampson, Acigona (Syn = Coniesta ignefusalis Hampson) and Mussidia nigrivenella Roganot were assessed in 17 and 6 small-scale farmers' fields in southwestern Nigeria during the early and late cropping seasons of 1991, respectively. The incidence, numbers of borer larvae and pupae as well as the damage caused were significantly higher in the late compared to the early season. Eldana saccharina and S. calamistis were the most abundant species while A. ignefusalis and B. fusca occurred in lower numbers at harvest. Mussidia nigrivenella occurred only during the late season. Eldana saccharina (r=0.96) and S. calalmistis (r=0.88) caused the highest percentage stalk length damage while A. ignefusalis (r=0.76) and E. saccharina (r=0.53) accounted more for the percentage node damaged during the early season. During the late season, B. fusca significantly increased the percentage nodes damaged (r=-0.86) while A. ignefusalis significantly reduced yield (r=-0.998). Combining the data for the two seasons revealed that 94.8% of the variation in yield was accounted for by cob weight, percentage of node damaged, number of plants damaged and the incidence of stemborers per farm. The percentage length damaged accounted for 30.9% of the variance in cob weight, while the number of S. calamistis per stalk accounted for another 17.7%. Of the variance in cob weight, 18.7% were accounted for by the total number of stemborers per stalk. The need to further investigate factors affecting oviposition choice by female maize stembores is highlighted. La frequence et les degets des foreuses des tiges du Mais, Eldana saccharina Walker, Sesamia calamistis Hampson, Acigona (Syn = Coniesta ignefusalis Hampson) et Mussidia nigrivenella Roganot ont ete evalues dans 17 et 6 champs de paysans du Nigeria, respectivement au debut et a la fin des saisons de culture en 1991. Cette evaluation fait partie d'un project visant a identifier les contraintes de la production du Mais dans la region. La frequence, le nombre de larves d'insectes et de chrysalides et les degets causes etaient sensiblement eleves a la fin de la saison de culture comparativement a ceuxs trouves au debut de la saison de culture. E. saccharina et S. calamistis etaient les especes les plus abondantes alors que A. ignefusalis et B. fusca se sont presentes en nombres reduits. Mussidia nigrivenella s'est presente seul