Insecticide Resistance in Spodoptera exigua (Lepidoptera: Noctuidae) Populations in Shallot Areas of Java, Indonesia

The beet armyworm, Spodoptera exigua (Hübner), is a major insect pest in shallot in Java, Indonesia. To control this insect, farmers rely on the use of a narrow spectrum of insecticides leading to resistance development. The objective of this study was to determine the level of resistance of S. exigua populations from different areas of Java to the most widely used insecticides, chlorfenapyr, methomyl, and emamectin benzoate, as well as to cyantraniliprole which was recently introduced in Indonesia. Spodoptera exigua populations were collected from three major shallot production areas in Java, the Districts of Brebes, Nganjuk, and Bantul. Based on the LC50 values, resistance ratios of S. exigua populations compared to the most susceptible population from the sub-district Pundong in Bantul varied from very low to very high: 1.1- to 113.8-fold for chlorfenapyr, 16.4- to 223.6-fold for methomyl, and 1.5- to 51.7-fold for emamectin benzoate. Spodoptera exigua populations from the same location were more susceptible to cyantraniliprole, with a resistance ratio of 4.0- to 12.1-fold. These findings indicate that the field populations of S. exigua collected from major shallot areas in Java were resistant to chlorfenapyr and methomyl and less resistant to emamectin benzoate, whereas they were still susceptible to cyantraniliprole. The populations from Brebes and Nganjuk were more resistant to chlorfenapyr, methomyl, and emamectin benzoate than those collected from Bantul. To prevent the further increase of resistant of S. exigua populations, IPM principles need to be applied including the alternate use of insecticides with different modes of action.