Pathogenicity and performance of two candidate isolates of Metarhizium anisopliae and Beauveria bassiana (Hypocreales: Clavicipitaceae) in four liquid culture media for the management of the legume pod borer Maruca vitrata (Lepidoptera: Crambidae)

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Research Papers

Introduction

Cowpea Vigna unguiculata (L.) Walp. (Fabaceae) is the most important grain legume crop in sub-Saharan Africa (Adati et al., 2008; Dugje et al., 2009). It is highly proteinaceous, well adapted to different soil types and intercropping systems, and resistant to drought with proven ability to improve soil fertility and prevent erosion (Adati et al., 2008; Dugje et al., 2009). The sale of stems and leaves as animal feed during the dry season is a major source of income for smallholder farmers across Africa (Langyintuo et al., 2003; Adati et al., 2008; Dugje et al., 2009). Despite its importance in improving food security and alleviating poverty, growers consider cowpea production risky due to the plethora of insect pests that attack the crop (Singh and Allen, 1979; Singh and Emden, 1979; Jackai and Daoust, 1986; Adati et al., 2008). Moreover, infestation can cause up to 100% yield loss if not effectively controlled (Dugje et al., 2009). Among these different insect pests, the legume pod borer Maruca vitrata (Fabricius) (Lepidoptera: Crambidae) is regarded as one of the most important pests, causing yield losses of 20-100% (Karel, 1985; Sharma, 1998; Ranga Rao and Shanower, 1999; Sharma et al., 1999; Srinivasan, 2012). For example, in Kenya, losses of up to 80% are common on different varieties of cowpea (Okeyo-Owuor et al., 1983). Infestation starts in the terminal shoots, later spreading to the reproductive structures with the larvae feeding on floral buds, flowers and pods (Jackai, 1981; Sharma, 1998). Currently, the majority of smallholder farmers who produce the bulk of cowpea across Africa rely exclusively on chemical insecticides to combat damage due to M. vitrata with little guidance on their use and application frequency. The direct consequences of inappropriate application and overuse are destruction of indigenous natural enemies, pesticide resistance and human and environmental hazards (Okeyo-Owuor et al., 1983; Ekesi, 1999; Ton, 2000; Ulrichs et al., 2001; Chopra et al., 2005). Resistance by M. vitrata to commonly used insecticides, including organochlorines, organophosphates, carbamates and synthetic pyrethroid compounds has been documented in Kenya (Okeyo-Owuor et al., 1983), Benin (Atachi and Sourokou, 1989), Nigeria (Ekesi et al., 1995)...