Wednesday, December 12, 2007 - 10:17 AM

Biological control in rice: Testing the role of manure in enhancing predation

Yolanda H. Chen, and Carmencita C. Bernal, International Rice Research Institute, Crop and Environmental Sciences Division, DAPO 7777, Metro Manila, Philippines

Tropical irrigated rice is a system of extraordinary biological diversity and a high level of natural biological control. There is mounting evidence that adding animal manure further enhances biological control, by supporting detritivorous insects that become prey to terrestrial predators. Later in the season, terrestrial predator populations then switch to feed on insect pests. In order to develop clear and simple guidelines for resource-poor farmers in the developing world, our study examined if manure inputs could enhance biological control in general. Our goals were to: 1) determine the relative importance of manure inputs and host plant resistance on stem borer damage, and 2) examine the relationship between manure inputs and biological control of three common pests: the rice leaffolder, Cnaphalocrocis medinalis, the brown planthopper, Nilaparvata lugens, and the yellow stem borer, Scirpophaga incertulas. The study consisted of fertilizer treatments (composted chicken manure or chemical fertilizer), and four varieties (IR56, IR62, IR70, and IR72) that varied in their resistance to insect pests. Egg masses and sentinel insects were introduced into subplots. Manure inputs lowered stem borer damage, but the difference between fertilization treatments varied among varieties. Higher manure inputs improved biological control in general, by decreasing the abundance and damage of all pests. Given that animal wastes are a growing source of pollution in developing countries, channeling animal manure into rice production has the potential to increase biological control and sustain environmental quality.

Species 1: Lepidoptera Crambidae Scirpophaga incertulas (yellow stem borer)
Species 2: Hemiptera Delphacidae Nilaparvata lugens (brown planthopper)
Species 3: Lepidoptera Pyralidae Cnaphalocrocis medinalis (rice leaffolder)