Control of the beet armyworm, Spodoptera exigus (Huebner), on welsh onion [Allium fistulosum] by synthetic sex pheromone at Yodo district, Kyoto [Japan]

Control effect of the synthetic sex pheromone against Spodoptera exigua (Huebner) (Lepidoptera: Noctuidae), a pest of welsh onion, was examined at Yodo district, Kyoto city. The pheromone sealed in a polyethylen tube, Yotocon S (Shin-etsu Chemical Co. Ltd.), was set in the welsh onion field (2.8 ha) at the rate of 180 tubes/10a from last June to December, 1994. The effect of communication disruption of the pheromone was monitored by the pheromone trap and the mating test using tethered virgin females in the onion field. And the rate of damage to welsh onion by larvae was biweekly examined in both treated and untreated fields from June to December. In addition, a light trap was set at 13m height of the building near the field for checking the adult flight activity during the season. The results of the pheromone trap catches and the mating test showed that the pheromone was effective in disrupting their communication. The rate of damage to the plant in the treated field was flower than that of untreated fields from June to September. However, the control effect was decreasing from October when the species was high in density. This may be due to the invasion of mated females and larvae into the treated fields from untreated ones outside, or through accidental introduction by man at transplanting. At the pheromone traps adult males began to collect from April and they gradually increased in number from June, and they were still in a high number up to October. In contrast, at the light trap the adult males and females were first collected at last of August and they were intensively caught form mid September to November. The flight activity of this species may increase in autumn