Natural Enemies of Fall Armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae) in Different Agro-Ecologies

Fall armyworm (FAW) Spodoptera frugiperda (J.E. Smith) and southern armyworm (SAW) Spodoptera eridania (Stoll) have become major threats to crops in Africa since 2016. African governments adopted emergency actions around chemical insecticides, with limited efforts to assess the richness or roles of indigenous natural enemies. Field surveys and laboratory studies were conducted to identify and assess the performance of parasitoids associated with spodopterans in Cameroon. FAW was the most abundant spodopteran pest. Telenomus remus (Nixon), Trichogramma chilonis (Ishi), Charops sp. (Szépligeti), Coccygidium luteum (Cameron), Cotesia icipe (Fernandez & Fiaboe), and Cotesia sesamiae (Cameron) are the first records in the country on spodopterans. Telenomus remus, T. chilonis, C. icipe, and Charops sp. were obtained from both FAW and SAW; C. luteum and C. sesamiae from FAW. The distribution of spodopterans, their endoparasitoids, and parasitism rates varied with host, season and location. In the laboratory, T. remus showed significantly higher parasitism on FAW than SAW, and significant differences in the development parameters between the two host eggs, with shorter development time on FAW. It induced significant non-reproductive mortality on FAW but not on SAW. Developmental parameters showed that C. icipe has a shorter development time compared to other larval parasitoids. Implications for conservative and augmentative biocontrol are discussed.

Spodoptera eridania (southern armyworm).

Spodoptera eridania is a polyphagous generalist feeder recorded on 200 plants species belonging to 58 botanic families. It is native to the USA and occurs throughout southern USA, Central and South America, and the Caribbean (Pogue, 2002). Due the fact that S. eridania occurs all across the USA and is present in many host plants, several regions around the world are in risk of invasion due to the global trade of vegetables, ornamental and aromatic plants, which can transport larvae and eggs. Even though it is not established in Europe, it has been detected on imported plants from the New World (Karsholt, 1994). The detection of S. eridania in Africa, demonstrates its high dispersal ability, indicating the importance of closely monitoring this species.

Insecticidal Activity of a Vip3Ab1 Chimera Is Conferred by Improved Protein Stability in the Midgut of Spodoptera eridania

Vip3A proteins are important for the control of spodopteran pests in crops, including Spodoptera frugiperda (fall armyworm). Native Vip3Ab1 controls S. frugiperda, but it is ineffective against S. eridania (southern armyworm), a major pest of soybean in South America. Recently, a Vip3Ab1 chimera with a modified C-terminus was described, Vip3Ab1-740, which has increased potency against S. eridania while maintaining activity against S. frugiperda. As S. frugiperda and S. eridania are differentially susceptible to Vip3Ab1, experiments were conducted to identify and understand the mechanism by which this expanded potency is conferred. The role of protein stability, processing, and in vivo effects of Vip3Ab1 and Vip3Ab1-740 in both of these species was investigated. Biochemical characterization of the midgut fluids of these two species indicated no obvious differences in the composition and activity of digestive enzymes, which protease inhibitor studies indicated were likely serine proteases. Histological examination demonstrated that both proteins cause midgut disruption in S. frugiperda, while only Vip3Ab1-740 affects S. eridania. Immunolocalization indicated that both proteins were present in the midgut of S. frugiperda, but only Vip3Ab1-740 was detected in the midgut of S. eridania. We conclude that the gain of toxicity of Vip3Ab1-740 to S. eridania is due to an increase in protein stability in the midgut, which was conferred by C-terminal modification.

Complete Genome Sequence of an Alphabaculovirus from the Southern Armyworm, Spodoptera eridania

We report the complete genome sequence of a baculovirus from the moth Spodoptera eridania, the southern armyworm. The genome sequence is 149,090 bp and exhibits the greatest degree of sequence similarity with genomes from alphabaculoviruses isolated from other moths of the genus Spodoptera.