Responses of selected corn varieties to Asian corn borer

The damage caused by Asian corn borer (ACB), Ostrinia furnacalis Guenee, exerts heavy toll on corn production. ACB damage results in 20-80 percent yield loss and complete crop failure during severe infestation. Moreover, the presence of different ACB ecotypes in corn growing areas such as Camarines Norte poses a problem in the usefulness of resistant cultivar. Mostoles et al. (CSSAC) monitored the ACB from June 2004 to April 2005 to determine the field infestation cycle, quantify the damage, and assess the infective ability of ACB ecotypes through the field responses of selected corn varieties. The researchers determined the occurrence of variable populations or different strains of ACB through examination of the field reaction of varieties (NK8840, 'Tiniguib', 'Lagkitan', Philippine Super Sweet, C818, and APB911) to the local ACB population. Standard cultural management practices were followed to minimize experimental error. Infestation during the WS [wet season] was greater than in the DS [dry season] as manifested by the greater number of larvae and pupae; pinholes, slot hole, and lesion; higher percentage of broken stalks and tassels; and many borer holes and tunnels. The weather condition was favorable to the survival of ACB adult. Higher population of insect pest was evident at 50 days after planting (DAP) and lowest at 30 DAP. Natural enemy population were higher at 40-50 DAP and lowest at 30 DAP. Significant damage differed among the varieties. Tiniguib and NK8840 were preferred for oviposition and larval feeding during the early whorl. At the late whorl and tasselling stages, the Philippine Super Sweet was preferred and has the highest larval count and number of pinholes, damaged ears, borer holes, and tunnels. NK8840 and C818 had the least damage. Lagkitan and Tiniguib had higher percentage of broken tassels and stalks while NK8840, IPB 911, and C818 showed the lowest. Zero parasitization of ACB egg mass, larva, and pupa was observed although predators such as Chryson sp., mantispidae, earwigs, odonatans, and hymenopterans were many. Grain yield was highest in NK8840, C818, and IPB911 while Philippine Super Sweet has the lowest yield. Yield loss was 30-66 percent, with Philippine Super Sweet corn having the biggest yield loss and NK8840 and C818, the least. Since the study was conducted only in two-season production in Camarines Sur, there is a need to conduct another trial in other parts of the Bicol Region to confirm the results. There is also a possibility that different ACB ecotypes exists in other areas that may affect corn production.