Infestation and damage on three maize cultivars by the stalk-borer Chilo partellus (Swinhoe) in relation to their yield in western Kenya

The effects of infestation and damage by the stalk-borer, Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae), were studied in the field on the grain yield of the following maize cultivars: Inbred A (susceptible), ICZ2-CM (resistant) and Katumani Composite B (a commercial early maturing cultivar). Borer infestation levels (egg-population density and larval-pupal population density) and damage levels (foliar damage and stalk damage) were significantly lower during the long rainy season of 1984 than 1985, On Inbred A, oviposition by the moths during the pre-flowering and flowering stages was much more important in causing a reduction in the grain yield than that during the post-flowering stage of the crop. There was no correlation with grain yield on ICZ2-CM and Katumani. The larval-pupal population density on Inbred A (but not on ICZ2-CM or Katumani), had a significant negative correlation with grain yield. Foliar damage and stalk-tunnelling by the borer only affected the grain yield of Inbred A. Under artificial infestation, the grain yield of Katumani is reduced significantly by the borer attack, but under natural infestation it escapes due to its early maturity. By comparison, ICZ2-CM has inherent resistance to C. partellus and Infestation and damage by the borer have no effect on grain yield.