Field observations on Chilo infestation of 100 promising sorghum lines showed that there are six levels of relationship affecting plant colonization and damage level by stem-borers: non-preference for oviposition (E 302, E 303, IS 1044, IS 1151, IS 2162, IS 4660, IS 17739, IS 18328, IS 18349, IS 18479, and IS 18489); feeding of the first larval instars on young leaves (reduced on E 302, E 303, IS 1044, IS 2162, IS 2209, IS 18349 and IS 18427); causing of ‘dead hearts’ by young larval instars due to extensive feeding in stems of young plants (lower for IS 2162, IS 2263, IS 18328, IS 18349); tunnelling (extent and location) of older instars in stems (low in IS 4660, IS 18427 and IS 18479); tolerance of plants to leaf damage (in spite of high damage, plants form panicles) (IS 2205); and tolerance of plants to larval feeding in stems (in spite of high tunnelling, the plants form seeds). The effect of a number of cultivars showing different levels and mechanisms of resistance on the Chilo behaviour and biology was studied in depth under field conditions.

The results of five experiments on maize resistance to Chilo partellus, suggest that there are at least five levels of relationships affecting plant colonization, larval survival and damage level: non-acceptance for oviposition shown by Inbred D and G and CIMMYT lines 125, 33, 324 and 178 (s3). Preferred Inbred A was oviposited 2–3 times higher. Feeding of young larval instars on young leaves or leaf sheaths, reduced on CIMMYT lines 324, 125 and 33; concentration of feeding of young larval instars on the upper growing part of plant, extensive on the highly susceptible Inbred A and reduced on all resistant lines tested; penetration of young larval instars into stem, reduced on CIMMYT lines 34 and 125 and Inbred G; and feeding of older larval instars in stem, reduced on CIMMYT lines 324, 178, 125 and Inbred G.