Demand-Driven Technologies for Sustainable Maize ... - IITA

324on insect infestation and the associated yield loss. The reason for thedifferences in the results could be due to the fact that different cropswere investigated in the two studies and the focus in Ta’Ama’s studywas on cowpea insects in general and not on stem borers.Data obtained in the present study suggested that Nyom II, wherestem and cob borers were more abundant with more severe damage,could be an effective location for the screening of maize germplasmfor stem borer resistance. Similarly, the higher number of earwigs inBafi a (51% of the total) provides an explanation for the lower numberof borers found at that location. In addition, intercropped plotscontained more predators than the other plots. These results seem tocorroborate the natural enemies hypothesis proposed by Root (1973).According to this author, a pest is suppressed because of the increaseof an environment favorable to predators, parasites, or pathogens inan intercropping system. Natural enemies may increase in abundancein an intercrop because of more continuous availability and diversityof nutritional resources (preys, pollens, nectars) and shelters. Althoughthere is no evidence that companion crops were a source that enrichedthe fauna of maize agro-ecosystems, it could be assumed that thepresence of cowpea could have improved the soil cover, which is oneof the most important elements of the microenvironment favorable tothe survival of the earwig (Van Driesche and Bellows, 1996).Results of the species diversity indexes obtained in the present studyalso indicated that predator species were more equitably distributedin Bafi a than in Nyom II. The low number of predators (especially D.erythrocephala) observed in the treated plots (Table 5) may partly beexplained by the fact that the insecticide used might have eliminatedsome natural enemies present in these plots. These results, therefore,emphasize the incompatibility between Carbofuran and D. erythrocephalaif used in the same integrated pest management program.An additional benefi t of 268 495 FCFA has been derived fromintercropped plots showing their superiority over the other treatments.Cowpea is also a prestigious food sold for more than four times theprice of maize in the local markets. In addition, the N-fi xing abilityof cowpea could improve the soil fertility. Reynolds et al. (1993)reported an increase in the N output of cereal-intercropped systemsinvolving cereal and N-fi xing legume crops, with the N coming largelyfrom the legume. Two mechanisms are known to be involved in theimprovement of the N status of a cereal associated with a legume: thenitrogen transfer (lateral movement and/or transfer to the subsequentcrop) and the sparing use (or effect) of the soil mineral nitrogen by thelegume, thereby leaving more to be exploited by the cereal (Giller andWilson 1991; Giller et al. 1991).