Combined Effects of Sampling Dates, Insecticide Treatment and Cropping System on Bruchids (Coleoptera: Chrysomelidae: Bruchinae) Oviposition and Egg Parasitism by Uscana lariophaga Steffan, 1954, (Hymenoptera:Trichogrammatidae) in Cowpea Vigna unguicula
Koï Wenceslas Kam *
Université Yembila Abdoulaye TOGUYENI, Institut Supérieur du Développement Durable, BP 54 Fada N’gourma, Burkina Faso and Laboratoire d'Entomologie Fondamentale et Appliquée, UFR/SVT, Université Joseph KI-ZERBO, Burkina Faso, 06 BP 9499 Ouagadougou, Burkina Faso.
Jean Christophe Koussoube
Laboratoire d'Entomologie Fondamentale et Appliquée, UFR/SVT, Université Joseph KI-ZERBO, Burkina Faso, 06 BP 9499 Ouagadougou, Burkina Faso and Centre Universitaire de Tenkodogo/Université Thomas Sankara, 12 BP 417 Ouagadougou 12, Saaba, Burkina Faso.
Marcellin Yamkoulga
Laboratoire d'Entomologie Fondamentale et Appliquée, UFR/SVT, Université Joseph KI-ZERBO, Burkina Faso, 06 BP 9499 Ouagadougou, Burkina Faso and Laboratoire de l’Environnement et des Ecosystèmes Forestiers, Agroforestiers et Aquatiques (Labo EcoFAA), Centre National de la Recherche Scientifique et Technologique (CNRST), BP 7047, Ouagadougou, Burkina Faso.
Antoine Waongo
Centre National de la Recherche Scientifique et Technologique (CNRST), Institut de l’Environnement et de Recherches Agricoles (INERA), Département Productions Végétales (DPV), Laboratoire de Protection et Défense des Cultures (LAPRODEC), 04 BP 8645, Ouagadougou 04, Burkina Faso.
Zakaria Ilboudo
Laboratoire d'Entomologie Fondamentale et Appliquée, UFR/SVT, Université Joseph KI-ZERBO, Burkina Faso, 06 BP 9499 Ouagadougou, Burkina Faso.
Antoine Sanon
Laboratoire d'Entomologie Fondamentale et Appliquée, UFR/SVT, Université Joseph KI-ZERBO, Burkina Faso, 06 BP 9499 Ouagadougou, Burkina Faso.
*Author to whom correspondence should be addressed.
Abstract
Background: Cowpea production is affected by bruchid infestation, while the indigenous egg parasitoid Uscana lariophaga contributes to natural mortality of bruchid eggs.
Aims: This study aimed to evaluate the combined effects of cowpea Vigna unguiculata (L.) Walp. phenology, insecticide application and cropping system on the oviposition dynamics of Callosobruchus maculatus (F.) and Bruchidius atrolineatus Pic. and on egg parasitism by the indigenous parasitoid Uscana lariophaga Stef.
Study Design: A 3 × 2 factorial arrangement was used, comprising three cropping systems (cowpea monocrop, cowpea–millet intercrop and cowpea–sorghum intercrop) and two insecticide regimes (untreated control and insecticide-treated), with four independent plots per combination, giving 24 plots in total.
Place and Duration of Study: The experiment was conducted at Gampela, approximately 20 km from Ouagadougou, in the North Sudanian agroecological zone of Burkina Faso, over two consecutive growing seasons.
Methodology: Field experiments were conducted using cowpea, cultivar KVX 61.1. In each cropping system, insecticide-applied and control plots were monitored. Twenty-five cowpea pods were marked weekly and subsequently examined for bruchid egg laying and eggs parasitised by the indigenous parasitoid U. lariophaga Stef.
Results: Insecticide application significantly reduced oviposition by both bruchid species across cropping systems and years (P < .001). In control monocrop plots, mean oviposition by C. maculatus reached 60 eggs at 71 DAS, compared with 20.75 eggs in treated plots, while B. atrolineatus reached 122 and 24.75 eggs, respectively. Similar reductions occurred in both intercropping systems. Parasitised egg numbers were generally higher in untreated plots and varied with sampling date, cropping system and year.
Conclusion: The 64–71 DAS period was critical for bruchid oviposition. Integrating cowpea phenology and cropping-system configuration into insecticide timing while conserving U. lariophaga may improve integrated management of cowpea bruchids.
Keywords: Cowpea, Vigna unguiculata, bruchids, Callosobruchus maculatus, Bruchidius atrolineatus, Uscana lariophaga, egg parasitism, insecticide treatment, cropping systems, host-plant phenology, integrated pest management