Populations of the Brown Planthopper, Nilaparvata lugens (Stål) (Homoptera: Delphacidae), and Its Predators on Rice Varieties with Different Levels of Resistance

Abstract

Rice varieties with different levels of resistance were evaluated in the green-house and insectary to determine their effect on populations of brown planthoppers, Nilaparvata lugens. In the absence of predators, N. lugens mortality was highest on the resistant (R), intermediate on the moderately resistant (MR), and lowest on the susceptible (S) varieties. When predators were added to the cages, N. lugens mortality increased on all varieties but was highest on the R varieties. When the effect of varietal resistance on N. lugens mortality was eliminated by using Abbott's formula, predation by the spider, Lycosa pseudoannulata, was highest on the R varieties at a ratio of 20 N. lugens per spider. In a field study, N. lugens populations at 40 days after transplanting were lowest on the R varieties, whereas predator populations were similar on all varieties irrespective of their level of N. lugens resistance. The prey-predator ratio on the R varieties was, thus, most favorable for effective biocontrol. The field test indicated that moderate levels of N. lugens resistance were beneficial when combined with activity of natural enemies because N. lugens populations remained below the economic threshold in the R and MR varieties, whereas the economic threshold was surpassed on the S varieties.