Dinamika Populasi Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae) pada Pertanaman Bawang Merah di Dataran Rendah

Abstract

Population Dynamics of Spodoptera oxigua (Hiibner) (Lepidoptera: Noctuidae) on Shallot Fields in Low-land The research was conducted in sub-district of Ciledug (Cirebon) with the objectives to study the infestation and larval population development of onion armyworm, Spodoptera exigua (Hiibner) (Lepidoptera: Noctuidae), on shallots grown in lowland. Monitoring of egg masses and leaf damage were made at 3-4 days interval while of larvae at 1 week interval. Outbreak took place during the dry season of August-October 1995 when population density reached 0.8 egg mass and 23 larvae per hill, and subsequently all hills were heavily damaged. Throughout the rainy season of December 1995-February 1996, egg masses and larvae were dz@cult to find. Results of hand-picking showed that larvalpopulation during dry season was 78 times higher than those of rainy season. Larvae exhibited body color variations. During the epidemics 80% of the larvae were dark whereas during the endemics only lo%, the rest were light green. Level of egg parasitization was 0.9% caused by Trichogramma sp. (Hymenoptera: Wchogrammatidae) and Telenomus sp. (Hymenoptera: Scelionidae), and larval parasitization 5.7% caused by Microplitis sp. (Hymenoptera: Braconidae), Euplectrus sp. and Stenomesius sp. (Hymenoptera: Eulophidae), and Peribaea sp. (Diptera: Tachinidae). Low level of parasitization together with the abundance of food supply and dry season were believed to be the main factors contributing to the population outbreaks. Hand-picking of egg masses and larvae conducted regularly, as practiced by the farmer p u p in the village of Dukuh Wringin (Brebes), should be adopted as a key activity for mitigating S. exigua infestation during dry season; and therefore, this practice should be disseminated to fanners in other areas.