Population dynamics of corn borer in relation to corn varieties

Results revealed that corn borer larva had the most number of both Cargill and Pioneer 3246, with mean averages of 37.50 and 36.75, respectively. In Cornworld and IPB 911, the mean averages were 26.50 and 18.0, respectively. Results of the study showed that at early whorl-stage, corn borer larva was highest in Cargill. It increased at mid-whorl to silking stages in other corn varieties. However, there was a decrease in number during the maturity stage. The total mean of corn borer larva was found highest in Cargill with 37.50, followed by Pioneer 3246, Cornworld, and IPB 911 with 36.75, 26.50, and 18.0, respectively. No corn borer eggmass was observed in IPB 911 and Cornworld varieties during all crop stages. However, eggmasses were noted in Cargill at mid-whorl up to tasseling stages; and in Pioneer at late whorl to silking stages. Likewise, no corn borer pupa was observed at early whorl up to late whorl stages in all corn varieties. However, it was noted in cornworld at tasseling and at Cargill and Pioneer 3246 at silking stage, and increased during maturity stage in all corn varieties. Pioneer 3246 and Cargill obtained the same mean of 13.75, followed by Cornworld with a mean of 8.0. IPB 911 obtained the lowest mean of 5.0. Corn borer was not present in all corn varieties at early whorl, mid-whorl, and maturity stages. It was noted only in Cargill both at late-whorl and tasseling stages, and in Pioneer at silking stage. Other corn pests such as corn earworm and cutworms were also present in all corn varieties at different growth stages, except at maturity stage. Corn earworm was highest in number in Pioneer 3246 with an average of 7.25, followed by Cargill, Cornworld, and IPB 911 with a total mean of 6.75, 2.25 and 2.0 respectively. Cutworm incidence was highest in Cargill variety with a total mean of 4.75. Predators such as coccinelid beetles, spiders, and long-horned grasshoppers were also present in all corn varieties at different growth stages. Coccinelid beetles, which prey on corn borer eggmasses and aphids, were found highest in Cornworld variety which gained a total mean of 37.25; followed by Cargill and Pioneer 3246 which earned the same average of 32.50; and was found lowest in IPB 911 which had a mean average of 31.0. Spiders, which prey on many different insect species, were highest in Cargill with an average of 10.25 followed by Cornworld, Pioneer, and IPB 911, which gained averages of 9.25, 7.25 and 5.25, respectively. Long-horned grasshoppers, which as also predators of many insect pests, were highest in IPB 911 with a total mean of 3.0 followed by Cargill and Cornworld with the same average of 2.5 and lowest in Pioneer 3246 with a mean of 1.5. The dominant weeds present in the area were: Paspalum distichum (maliit na kalabaw), Cyperus rotundus (mutha), and Amaranthus spinosus (kulitis). Statistical analysis showed no significant differences among the treatments. This suggests that in spite of the considerable number of corn borer larva, Pioneer 3246 obtained the highest yield of 8.1 t/ha. IPB 911 and Cargill followed, with means of 7.4 t/ha and 7.3 t/ha, respectively. The lowest yield was noted in Cornworld variety, which gave an average of 6.9 t/ha. Pioneer 3246 was a tolerant variety, which can produce satisfactory grain yield in spite of borer infestation