Vol. 15(1), pp. 113-121, January, 2020 DOI: 10.5897/AJAR2019.14391 Article Number: 4EC707B62779 ISSN: 1991-637X Copyright ©2020 African Journal of Agricultural Author(s) retain the copyright of this article http://www.academicjournals.org/AJAR Research Full Length Research Paper Management of the legume pod borer Maruca vitrata Fabricius (Lepidoptera: Crambidae) with field applications of the entomopathogenic fungus, Beauveria bassiana and a mixed formulation of the baculovirus MaviMNPV with emulsifiable neem oil Joelle Toffa Mehinto1,2*, Yeyinou Laura Estelle Loko1, Ouorou Kobi Douro Kpindou2, Elie Ayitondji Dannon2, Karimou Zanzana2, Parfait Kassa2, Appolinaire Adandonon3 2 and Manuele Tamò 1Laboratory of Applied Entomology, Faculty of Sciences and Technology of Dassa (FAST-Dassa), National, University of Sciences Technologies Engineering and Mathematics of Abomey (UNSTIM), BP 14, Dassa, Benin. 2International Institute of Tropical Agriculture, 08 BP 0932 Cotonou, Benin. 3School of Crop and Seed Production and Management (EGPVS), University of Agriculture of Ketou (UAK), 08 BP1055 Cotonou, Benin. Received 12 August, 2019; Accepted 4 November, 2019 The present study assessed the effectiveness of the entomopathogen fungus Beauveria bassiana in comparison with neem oil combined with the baculovirus MaviMNPV and a synthetic insecticide deltamethrin for the control of Maruca vitrata Fabricius under field conditions. The trial was conducted in six villages at Glazoue and Djakotomey, two districts in Benin. Four treatments consisting of (1) untreated control, (2) neem + MaviMNPV, (3) B. bassiana and (4) deltamethrin were arranged in a complete randomized block design with three replicates. Reproductive organs of cowpea plants were sampled for estimating population of M. vitrata. In spite of the importance between-field variations observed, bio-pesticides significantly reduced the population density of M. vitrata as well as its damage level. Similarly, grain yields were improved in sprayed cowpea compared to the untreated control, regardless of the experimental zone. In Glazoue, yields ranged from 724.06 ± 5.04 kg/ha (deltamethrin) to 933.03 ± 8.7 kg/ha (B. bassiana). In Djakotomey, 649.1±4.7, 611.07±5.1, 583.19±4.04 and 217.11±3.9 kg/ha were recorded for deltamethrin, B. bassiana, neem + baculovirus, and untreated control, respectively. The possibilities of the using bio-pesticides as efficient IPM components in cowpea are discussed. Key words: Cowpea pests, bio-pesticides, Beauveria bassiana, neem, baculovirus MaviMNPV, deltamethrin. INTRODUCTION Cowpea Vigna unguiculata L. (Walp) is one of the most regions of the world (Singh et al., 2002). It is also a important grain legumes in tropical and sub-tropical multipurpose crop grown as food and feed. Cowpea is 114 Afr. J. Agric. Res. cultivated worldwide with an estimated annual production close to cowpea, it was not possible to transfer the of 5.4 million tons with Africa producing nearly 5.2 million desirable genes into cultivated cowpea varieties because (FAOSTAT, 2015). Cowpea provides the cheapest of a strong cross-incompatibility at both pre and post- source of protein for human consumption (Ajeigbe and fertilization levels. Also, various cultural practices have Singh, 2006). Cowpea also is rich in vitamins and been tested but required additional chemical application minerals. Its leaves are also consumed as fresh to achieve efficient control (Oso and Falade, 2010). vegetables, while the plant after harvest is a valuable Hence, the only alternative to overcome damage by the source of fodder for cattle. The plant tolerates drought, cowpea pod borer M. vitrata remains biological control. It performs well in a wide variety of soils, and being a consists of using various living organisms such as legume, it replenishes low fertility soils through deposited predators, parasitoids and entomopathogens to control organic matter. Also, legumes play a key role in soil pests while maintaining biodiversity and reducing fertility improvement through biological nitrogen fixation production costs (Scholz et al., 1998; Girling, 1992). (Ajeigbe and Singh, 2006). Cowpea is grown mainly by Among the entomopathogenic organisms identified for small-scale farmers in developing regions. M. vitrata, the virus Maruca vitrata multiple In Benin, cowpea is the most cultivated and consumed nucleopolyhedrovirus (MaviMNPV) was highly specific to grain legume. In 2014, about 93488 tons of cowpeas M. vitrata (Lee et al., 2007). It was isolated from dead were produced in Benin on 115,000 ha (FAOSTAT, M. vitrata larvae in Taiwan, and was tested with 2015). It plays a role in human nutrition especially in success in West Africa against M. vitrata (Lee et al., rural areas characterized by unbalanced diet. However, 2007; Tamo et al., 2010; Sokame et al., 2015; Muhammad the production is low and only 6.12 Kg of cowpea grain et al., 2017). Likewise the entomopathogenic fungi such were supplied per capaiata per year (FAOSTAT, 2015). as Beauveria bassiana (Balsamo) Vuillemin Indeed, various constraints seriously limit cowpea (Hypocréales: Ophiocordycipitacea) are known for their production. Of these, biotic constraints namely damage ability to infect a wide range of insects including M. by insect pests remain the most important affecting vitrata (Srinivasan et al., 2014). In fact, the Beauveria both yield and quality of the harvested products (Egho, genus is mainly based on the special mode of conidial 2010). Of these, the legume pod borer, Maruca vitrata formation. Phialides carrying conidia are elongated Fabricius (Lepidoptera, Crambidae) is reported to cause sometimes spherical (Tanada and Kaya, 1993). In Africa serious damage on cowpea. The incidence of larvae of and particularly in Benin, B. bassiana has been used to the pest is all the more serious as each larvae attacks infect a wide range of insects in the field (Godonou et al., several organs of the same plant: Flowers, leaves, flower 2009; Douro Kpindou et al., 2011). Preliminary studies buds and green pods before migrating to another plant conducted in the laboratories of the International (Liao and Liu, 2000). The caterpillars destroy both Institute of Tropical Agriculture (IITA-Benin) on the third cowpea flowers and pods causing yield losses up to 80% and fourth instars of M. vitrata using the (Tamò et al., 2003). Indeed, its larvae, brown, yellow or entomopathogenic fungi, B. bassiana (isolate Bb115) light green at hatching, darken as they pass from one have shown that they are effective at various doses on stage to another. They are hairy, blackheaded with dark the pest (Douro Kpindou et al., 2011; Toffa Mehinto et al., brown spots on the body (Datinon, 2005). Several 2014a). The effect of B. bassiana was compared with that methods have been developed or tested against M. of Decis, a chemical pesticide commonly used in vitrata with chemical pesticides being the most used cowpea production in Benin and Neem + Virus already control means (Jackai, 1995). Chemicals application is no used in the biological control of cowpea pests (Sokame more attractive considering the so many side effects et al., 2015). including environmental pollution and human health This study aims to assess the effectiveness of the hazards, pest resistance and resurgence, secondary pest entomopathogen fungus B. bassiana in comparison with outbreaks and loss of biodiversity (Ekesi et al., 2002; the combination of neem oil and the virus MaviMNPV as Atachi et al., 2007). Alternative control methods such as alternative to synthetic chemicals in the context of pests’ host plant resistance and cultural control practices were management in cowpea. not much effective to keep insect pests populations below economic thresholds. Investigation on cowpea MATERIAL AND METHODS selection did not yield in lines demonstrating a satisfactory level of resistance to the pod. Only Vigna Experimental sites vexillata (L.) A. Rich, a wild Vigna was identified as highly resistant to M. vitrata. Although V. vexillata is The works described below were conducted at the laboratory *Corresponding author. [email protected] Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License Mehinto et al. 115 of insect pathology of the International Institute of Tropical Farmers' fields Agriculture (IITA), Benin Station (6°28N and 2°21E, 15 m altitude), near Cotonou, Benin, in climate chamber with a mean Six cowpea producers were selected from each of six sub- temperature of 26 ± 0.50°C and a relative humidity of 65.5 ± 5%. municipalities of Glazoue (Ouedeme) and Djakotomey The experiments were conducted also in two agro ecological (Djakotomey 1). The field experiments consisted of four zones of Central (Glazoue/Ouedeme) and Southern Benin treatments: Untreated control (no pesticide), cowpea treated with (Djakotomey/Djakotomey 1). Sites that hosted the experiments were Topbio (neem) + virus (MaviMNPV), cowpea treated with used to grow cowpea with different cropping systems. The climate Deltamethrin and cowpea treated with B. bassiana (isolate Bb at both sites is of Sudano-Guinean or subequatorial type, with two 115). Each treatment was repeated three times in a randomized 2 dry seasons alternating with two rainy seasons. The average rainfall complete block design (RCB) with experimental units of 100 m (10 ranged between 700 and 1100 mm per year at Djakotomey with m × 10 m). Cowpea was sown at 75 cm × 25 cm. Plants were temperature