A battle of armies: massive attack of natural enemies to the true armyworm Mythimna unipuncta (Haworth, 1809) (Lepidoptera: Noctuidae) in forage crops

Abstract

Understanding the interactions between plant-host-parasitoid plays a major role in insect pest management. Farmers in the southeastern United States rely on pasture systems for cattle milk and beef production, but the benefits of parasitoids and predators on major lepidopteran pests on pasture lands are still overlooked. Here, we aimed to identify and quantify the effect of parasitism on the true armyworm Mythimna unipuncta (Haworth, 1809) (Lepidoptera: Noctuidae) attacking teff grass Eragrostis tef (Zucc.) Trotter (Poaceae) and crabgrass Digitaria sanguinalis (L.) Scop. (Poaceae) in western Kentucky. In early August of 2023, 547 larvae of M. unipuncta were collected from experimental plots of teff, crabgrass, and the adjacent clover field. Larvae were weighed, and the number of attached tachinid eggs was recorded. The highest infestation of M. unipuncta was found on teff grass (34 ± 6 larvae/m2). We found 11 insect species of four families associated with the true armyworm, including parasitoids (n = 7), hyperparasitoids (2), and predators (2). The incidence (%) of parasitoid species was dominated by Winthemia rufopicta Bigot, 1889 (Diptera: Tachinidae) (91%), followed by Glyptapanteles militaris (Walsh, 1861) (Hymenoptera: Braconidae) (3%). The highest mortality of M. unipuncta was observed in larvae collected from crabgrass and teff grass samples (94% and 89%, respectively). This study underpins the importance of natural biocontrol on key pests and expands our understanding of multiparasitism on M. unipuncta in forage grasses of western Kentucky, showing that their collective impact can suppress the populations of noctuids in teff and crabgrass systems. Our results contribute to the basics of integrated pest management in forage systems.

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