Effect of agroecosystem diversity on natural enemies of maize stemborers in coastal Kenya

Abstract

A study was conducted at Mtwapa in the northern coastal area of Kenya during the long and short rainy seasons of 1999 and 2000 to assess the benefits of agroecosystem diversification—through agroforestry and intercropping—on the activity of natural enemies of maize stemborers. Treatments consisted of maize and cowpea intercrops or maize monocrops planted within hedgerows of Leucaena leucocephala and Gliricidia sepium. The plots were mulched or unmulched and insecticide-treated or not. The maize stemborers encountered, in order of abundance, were Chilo partellus, Chilo orichalcociliellus and Sesamia calamistis. The egg parasitoids Trichogramma spp. and Telenomus spp. were recovered from stemborer eggs. Ants, ladybird beetles, earwigs and crab spiders were found predating on the eggs. The larval parasitoids recovered included Cotesia sesamiae, Cotesia flavipes and Goniozus indicus, and the pupal parasitoid was Pediobius furvus. Mean rates of stemborer egg parasitism were generally high (> 70%) while larval and pupal parasitism rates were low (< 10%) for all the treatments. The observed rates of parasitism did not support the natural enemies hypothesis, which predicts that natural enemy activity increases with increasing agroecosystem diversity. Predation, larval and pupal mortality rates were generally low in all the treatments (< 10%), with no significant differences between treatments.