Biological control agents and levels of parasitism of Agrotis segetum (Lepidoptera: Noctuidae) in grain production regions of South Africa

Résumé

The management of the cutworm, Agrotis segetum (Denis & Schiffermüller) (Lepidoptera: Noctuidae), is challenging since the larvae spend most of their life cycle hiding underneath weeds or in the soil. Crop producers often report poor efficacy of chemical control, necessitating the development of alternative control strategies. Although many species of parasitoids and entomopathogenic nematodes (EPNs), have been reported from around the world where this pest occurs, no comprehensive list of these species exists, and little is known about their occurrence and impact as biological control agents in South Africa. A literature search yielded 75 parasitoid species, and six EPN species that parasitise A. segetum eggs and larvae. To assess the levels of parasitism in South Africa, cutworm populations were sampled from 14 different geographical regions, reared in a laboratory and monitored for parasitism and other mortality factors. The overall parasitism level recorded in this study was high (43.6%), with Macrocentrus collaris (Spinola) (Hymenoptera: Braconidae) being the most common (39.2%) parasitoid species, followed by Gonia bimaculata Wiedemann (Diptera: Tachinidae) (3.2%) and Periscepsia carbonaria (Panzer) (Diptera: Tachinidae) (1.2%). Entomopathogenic viruses were responsible for 26.1% of larval mortalities, while EPNs (Mermithidae) and entomopathogenic fungi caused 15.7% and 3.2% of mortalities, respectively. The incidence of parasitism, particularly by M. collaris, suggest that parasitoids could play a role in the suppression of A. segetum populations.

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