Relative abundance of fall armyworm ( <i>Spodoptera frugiperda</i> (J.E. Smith)) and maize stalk borer, <i>Busseola fusca</i> (Fuller) in Southern Ethiopia

Abstract Background: The fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), poses a significant threat to maize production in Africa. The impact of its invasion on the native maize stem borer, Busseola fusca (Fuller), the most important pest of maize in sub-Saharan Africa, has been a subject of high interest. Methods: Field surveys were conducted in 12 localities in southern Ethiopia in 2022 and 2023. Data on infestation, population density, and crop injury variables were collected. Farmers’ interviews assessed the use and storage period of maize residues, a key factor in the survival of B. fusca . Intraguild predation assays were conducted by introducing S. frugiperda and B. fusca neonate larvae at different times. Results: FAW larvae were the most abundant (60.3–98.1%) compared to B. fusca in all the study districts. The highest abundance of B. fusca was recorded in Meskan and Mareko (19.4–39.7%). Plant injuries caused by B. fusca were low, with 0.19–1.77 exit holes/plant, and 0.31–2.54% of tunneled stalk. Fewer than 0.67 larvae of B. fusca survived when introduced within 5 days after FAW infestation, followed by 1.50 and 1.17 larvae/plant when introduced after 7 and 8 days, respectively. Fewer than 0.33 B. fusca larvae per plant survived when FAW neonate larvae were introduced 3 days after B. fusca infestation. The number of B. fusca larvae that survived when introduced 9 and 12 days after FAW infestation was not significantly different from treatments without FAW (3.83 larvae/plant). Over 80% of farmers in Sidama and Wolaita store maize residues for animal feed and firewood for a few months, thereby eliminating potential sources of B. fusca infestation. In Meskan, the storage period extends until April. Conclusion: Our study highlights the displacement of the native maize stem borer, B. fusca , by the invasive FAW. The reduction in the maize residue storage period and predation by FAW contributed to the decline in the abundance and significance of B. fusca . However, B. fusca could still pose serious damage in areas like Meskan, where crop residues are stored for animal feed and firewood until the next cropping period.