Effects of Releases of the Egg Parastoid Uscana lariophaga Steffan (Hymenoptera: Trichogrammatidae) on Cowpea [Vigna unguiculata (L.) Walp.] Pods Artificially Infested with the Bean Weevil Callosobruchus maculatus Fabricius (Coleoptera: Chrysomelidae: Br

Abstract

Background : Cowpea production and storage are constrained by Callosobruchus maculatus, whose field infestation can continue after harvest. Aims : This study aimed to evaluate the efficacy of releasing the egg parasitoid Uscana lariophaga Steffan, 1954 against Callosobruchus maculatus (Fabricius, 1775) on cowpea (Vigna unguiculata (L.) Walp.) pods under greenhouse-like conditions. Site of the Study : The study was conducted at the experimental site of Joseph Ki-Zerbo University in Ouagadougou, Burkina Faso. Methodology : Four release regimes of U. lariophaga adults were evaluated. Two females per pot were released at 43 and 50 days after sowing (DAS) in U1; at 43, 50 and 57 DAS in U2; at 43, 50, 57 and 64 DAS in U3; and at 43, 50, 57, 64 and 71 DAS in U4. Each cage contained eight pots, corresponding to 32, 48, 64 and 80 females released in U1, U2, U3 and U4, respectively. A parasitoid-free cage served as the control (U0). Results : Cowpea pod infestation by C. maculatus increased progressively, reaching 57.5–67.5% at harvest. The highest number of eggs was recorded in U0 (66.75 eggs at 78 DAS), and egg numbers differed significantly among sampling dates (F = 29.22, P < 0.0001). The lowest mean number of eggs was recorded in U4, particularly between 50 and 57 DAS. Overall parasitism rates differed among release regimes, reaching 64.77% in U1 and 64.35% in U4. These rates were higher in U1 and U4 than in U2 and U3, with no significant difference between U1 and U4. At harvest, seed infestation was lower in U4 (2.96%) than in the control (5.70%), representing a 48.1% reduction. Conclusion : The five-release regime (U4) showed the greatest potential for reducing C. maculatus infestation and may therefore represent a promising biological control strategy.