Maize planting time and arthropod abundance in southern Mindanao, Philippines. I. Population dynamics of insect pests

Abstract

Monthly plantings conducted over 4 years in a rainfed triple maize cropping system in southern Mindanao, Philippines, revealed the Asian corn borer (ACB) Ostrinia furnacalis (Guenée) as the most important insect pest. Of minor importance and being restricted to one crop stage were rice seedling maggot Atherigona oryzae Malloch, thrips Thrips palmi Karny and Megalurothrips usitatus (Bagnall), corn leafhopper Cicadulina bimaculata (Evans), corn earworm Helicoverpa armigera (Hübner), and corn leaf aphid Rhopalosiphum maidis (Fitch). Farmers escape damage from ACB, seedling maggot, and thrips by planting the first crop in April. Planting of the second crop should be shifted from August to September to avoid ACB damage. Pest damage was low during the third crop, thus planting time is not an important consideration. Additional information on ACB bionomics was revealed in the study. Mean egg mass size was 36 eggs (range 1 – 169). Oviposition was found to be positively correlated with cumulative rainfall over the previous 3 – 8 weeks indicating that females seek healthy crops. Most (70%) oviposition occurred over a 4-week period in the 39 crops studied as a single peak between late-whorl through mid-tasseling stages when developing larvae would be more assured of feeding on the more nutritious pollen. The strong attraction of maize at early tasseling along with heavy parasitism in older maize become population synchronizing agents in the year round cropping study area, although less perfect than winters in temperate regions. Yield loss in southern Mindanao ranged from 20 to 49% which was more closely correlated with larval tunnels than moth exit holes. Correlations were significant only when damage was related to yield loss but not yield.