Spodoptera exigua (Hübner) is an important pest with wide host range including cabbage, beans, potato etc. We evaluate the virulence of Beauveria bassiana ARP14, B. bassiana GHA, and Isaria japonica with concentration of 1×108 conidia/mL against larval stage of S. exigua using glass scintillation vial. Lethal median time (LT50) of these three fungi was not found significantly different in both fourth and second instar. Infection rate was higher in fourth instar than second instar. Infection rate was highest by B. bassiana ARP14 (84.0%) followed by B. bassiana GHA (63.6%) and I. japonica (45.8%) in fourth instars of S. exigua. Our results suggest that B. bassiana ARP14 can be a new component of integrated pest management of S. exigua.

Control thresholds for the management of beet army worm, Spodoptera exigua (Lepidoptera : Noctuidae) were evaluated on welsh onion of two different planting time. Two inoculation times were tested for each planting and the number of inoculated larva was 5, 10, 20, 40 per twenty plants. The injured rate of leaves was 33.5% to 10.9% at 7th September at 40 to 5 larva inoculation plot on the five days planting. That of leaves was 20.5% at 40 larva on the twenty days planting. The yields of welsh onion on non-inoculation plot were 4,395 ㎏ per 10a. The rate of reduced yields was 49.2%(1,774.2 ㎏) and 36.5%(2,220.5 ㎏) at 40 larva inoculation on the 5 and 20 days planting, respectively. The linear relationships between population density and yield reduction were as following, it was Y=-43.474X + 3419.6 (R² = 0.9698) for 5 days and Y=-32.977X + 3518.9 (R² = 0.9928) for 20 days. Based on these results the control threshold level was estimated to be 1.8 larva for 5 days and 4.6 larva for 20 days per 20 plant. The more damaged leaves by S. exigua larva, the more yield reduction on welsh onion.