Impact of armyworm Spodoptera litura (Lepidoptera: Noctuidae) attack: Damage and loss of yield of three soybean varieties in South Sulawesi, Indonesia

This study aims to elucidate the relationship between the larval armyworm Spodoptera litura F. population density (0, 2, 4, and 6 per plant) with leaf damage level and yield loss in three soybean varieties, Anjasmoro, Argomulyo, and Grobogan. S. litura larvae were introduced both in the plant’s vegetative phase (20 and 30 days after planting) and its generative phase. This research used a split-plot design with the varieties as the main plots and the larval population as the subplot, with five replications. The results showed that the highest leafdamage was in the Anjasmoro, 6.5% to 8.87% in the vegetative phase and 6.95-7.81% in the generative phase. Meanwhile, Argomulyo had 5.96% to 6.68% and 5.78% to 6.39% of damage in both phases, and Grobogan was less susceptible, with 5.90% to 5.98% and 5.28% to 6.17% at the vegetative phase and generative phase, respectively. The highest decline in seed yield was in Argomulyo (0.81% and 0.79% in the vegetative and generative phase) and the lowest was Anjasmoro (0.66% and 0.64% in the vegetative and generative phase). For the population density, the highest level of soybean varieties seed yield loss in South Sulawesi was with 6 larvae per plant, which was at 23.44% in the vegetative phase and 23.48% in the generative phase. Among the varieties, the highest of seed yield loss was with Argomulyo (14.93%) and the lowest at Anjasmoro (11.30%). It can be concluded that the relationship between the S. litura larvae population density and the decrease of seed yield is quite strong (90.2% to 96.4% for vegetative phase and 94.8% to 96.4% for generative phase).