Efficacy study of selected maize (Zea mays L.) genotypes against the Asian corn borer, Ostrinia furnacalis (Guenee)

Laboratory and screen house studies were conducted to assess the efficacy of selected twenty-six maize varieties against Asian corn borer (ACB), Ostrinia furnacalis (Guenee). Hierarchical tree based on resistance parameters clearly revealed that the twenty-six maize varieties are best classified into three groups, viz. resistant, intermediate, and susceptible. In laboratory test, the varieties RCS2, RCS4, RCS5, 'IPB Var13', Bt2, Bt3, and Bt4 were consistently identified as highly resistant. Further examinations in stalk feeding assay showed that the resistant varieties had sharp decline in larval survival (LS) on the 2nd to the 5th day of larval feeding in stalk tissue. On the other hand, the susceptible varieties showed high LS across the 5-day feeding duration. This research highlighted that resistant maize varieties were mainly attacked below the ear nodes and internodes, with the most frequent observation on the 8th node below the ear node but had zero attack on the crucial ear node. Meanwhile, both the intermediate and the susceptible varieties were attacked on the ear node, with the feeding attacks distributed throughout the whole plant. This research provided further evidence that ACB resistance is available in Philippine native maize varieties. These experiments corroborate with previous results that transgenic maize expressing the Cry1Ab protein is lethal to ACB larvae. High resistance observed from the non-Bt 'IPB Var13' suggests that natural resistance is present. This research have presented that Bt varieties (Bt2, Bt3, Bt4) together with RCS2, RCS4 and 'IPB Var13' were the consistently resistant varieties in both laboratory and screen house assays. The plant resistance indices used in this study can effectively screen different varieties of maize in the Philippines. Further experimentations would be needed to determine the mechanism involved in the resistance and susceptibility of maize varieties infested with ACB.