An entomopathogenic fungus and a natural extract benefit rice (Oryza sativa) by suppressing populations of insect pests while keeping high populations of their natural enemies

Abstract

Sustainable and environmentally safe pest management often involves the use of natural enemies as an alternative to chemical means. For successful management of pests by natural enemies, a balanced population between insect pests and their natural enemies should be achieved. In this study, we compared such population balances in rice fields of Cambodia under the following conditions: no insecticide (NI), chemical pesticide-based conventional practice (CP), the use of a biopesticide (Beauveria bassiana, Bb), and the use of an orange oil extract (Oo). Treatment effects were evaluated by monitoring 17 species of insect pests and 15 species of natural enemies at two sites for two seasons. In the NI treatment, the level of natural enemies was the highest, however, the pest population density was also higher in this treatment than in the Bb and the Oo treatments, resulting in a low grain yield similar to that in the CP treatment notably in one trial. The Bb and the Oo treatments showed the lowest insect pest populations, although the Oo treatment had little impact on the populations of natural enemies. These results suggest that contributions of Bb and Oo treatments to decreasing pest populations were greater than those of the NI and the CP treatments, and that the Bb and the Oo treatments resulted in a favorable balance between populations of insect pests and their natural enemies. A high level of white earhead caused by stemborers resulted in significant yield losses in one trial. Among the four treatments in the trial, the Bb treatment resulted in the highest grain yield, and importantly, this treatment depressed the insect pest populations without much affecting the populations of their natural enemies. Overall, the results of this study suggest that the use of biopesticides in rice paddies is effective to keep the well-balanced population between insect pests and natural enemies by decreasing the serious pests such as stemborer and leaf folder that directly affect rice grain yields.