Role of inland valleys in the management of stem borers and their natural enemies in upland maize fields in the humid forest zone of Cameroon

During the dry season in the humid forest zone of Cameroon, maize is the most important off-season cash crop grown in hydromorpbic inland valleys (IVs), which may also be reservoirs for pests such as the stemborer Busseola fusca Fuller and its natural enemies. Pest and parasitoids were monitored in IVs and close-by upland maize fields from January 2002 through December 2004. Trap catches and oviposition data showed that B.fusca was active throughout the dry season and long and short rainy seasons of 2004. Egg batch densities were considerably lower in the dry than in the rainy seasons. important natural enemies were the scelionid egg parasitoids Telenomus busseolae Gahan and T.isis Polaszek. B.fusca was the predominant borer species in all seasons in maize in IVs as well as in upland fields, followed by Sesamia calamistis Hampson and Eldana saccharina Walker. B. fusca larval densities were lowest in the IVs and increased in the course of the year in the upland fields. In contrast, S. calamistis densities were higher in IVs than in upland maize fields. At harvest of the IV maize, B. fusca and E. saccharina larval densities were 47.3 and 15.5 times higher, respectively, than on old maize stubbles in upland fields planted during the previous year. Grain yields as well as the marketable ear index were 1.1-2 times higher in the dry season than in the long and short rainy seasons, indicating the importance of IVs for dry season maize production in Cameroon.