Author : Aganon, Teotimo M.

Summary : Insect pest colonization and succession were studied and the most susceptible stage to insect damage of soybean was determined. Evaluation of the different insect control strategies in soybean was conducted at the Experimental Area of the Research and Extension Office, Central Luzon State University, Mu¤oz, Nueva Ecija, the Philippines, from January 1987 to May 1988. The crop was colonized as early as 5 days after planting (DAP) by Phaneroptera furcifera Stal., Attractamorpha psittacina de Haan, and Epilachna philippinensis Dieke. Two days later, Ophiomyia phaseoli Tyron appeared. On the second week, lepidopterans like Lamprosema indicata Fabricius, Homona coffearia Nietner, Spodoptera litura Fabricius, Chrysodeixis chalcites Esper, Catachrysops onejus Fabricius, and Stomopteryx subsecievella (Zeller) were noted. At 32 DAP Etiella zinckenella Treitschke was noted. The most critical stages when crop was damaged by insect was during the pod filling (53 DAP) and beginning of seed formation (60 DAP). Plants that were defoliated during the late vegetative and reproductive stages had a higher percent yield reduction than those which were defoliated at early stage. The highest effect of defoliation on yield was at the beginning of seed formation stage. As the degree of defoliation increased, yield loss correspondingly increased. Levels of simulated pod injury significantly affected yield as manifested by increased yield loss from 0 to 100 percent pod injury level. Damage at podding, pod filling, and seeding showed significantly higher yield losses than damage at full seeding. Monocrotophos at the rate of 500 g ai/ha plus deltamethrin at 20 g ai/ha (recommended insecticides) outyielded all other insecticide treatments but it proved inferior in terms of return on investment (ROI) over the application of deltamethrin at 10 g ai/ha. Dipel (Bacillus thuringiensis var. kurstaki) at the rate of 20 grams/16 liters water was the most profitable of all treatments.