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

268on moderately resistant and susceptible genotypes. These observationsindicated a high non-preference for the genotypes thus further confi rmingtheir high level of resistance to S. calamistis. Low consumption index isan indication that less food was consumed or that the insect did notuse the consumed food properly. According to Alghali and Osisanya(1982), the degree of utilization of food consumed depends upon thedigestibility of the food and the effi ciency of conversion of the ingestedfood into body substances. In the present study, although there wereno signifi cant differences among genotypes with respect to growthrate, the digestibility of food ingested was low on resistant genotypes S511-1, S5 27-1 and S5 9-1, leading to antibiosis. However, the effi ciencyof conversion of the ingested food into body substances was higher inthese genotypes. This indicates that the digestible portion of ingestedfood from susceptible genotypes that was metabolised for energy tomaintain life was low. It may be concluded that the susceptible S520-2 and Tzmi 407 were not necessarily suitable for the growth ofS. calamistis. Similar observations have been made on other species(Alghali and Osisanya, 1982; Alghali and Saxena, 1988). Thus, thereis an urgent need to carry out detailed nutritional analyses of theseresistant and susceptible genotypes to determine the plant charactersinfl uencing the consumption of S. calamistis third instar larvae on stemtissues. In addition, the characters involved in the conversion of ingestedfood into body substances need to be identifi ed. Proper identifi cationand understanding of these two sets of plant characters could be apowerful tool for the management of S. calamistis.The different profi les obtained in this study showed genotypicvariation for the level of responses, which, in turn, suggests genotypicvariation in the plant characters responsible for a response. Therefore,if the plant characters are heritable, they may be manipulated throughappropriate breeding techniques to increase resistance in the genotypesevaluated in this study, or in populations developed from the genotypeswith high resistance and other suitable characters. Among the genotypesevaluated in the study, only S5 9-1 showed very low grades in theprofi les obtained from both choice and no-choice scenarios. Theseresults explain its high resistance to S. calamistis. On the contrary, S520-2 and Tzmi 407 elicited three responses in the medium to very highgrade in one scenario, and four responses in the medium to high gradein the second. It may, therefore, be concluded that S5 9-1 is resistant,while S5 20-2 and Tzmi 407 are susceptible to S. calamistis.AcknowledgementsThis research was fi nanced by the African Maize Stress (AMS)Project. We are grateful to the Institute of Agricultural Research forDevelopment (IRAD) and IITA for their technical support. We also wish