The potential for using entomopathogenic nematodes and fungi in the management of the maize weevil, Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae)

Maize (Zea mays L.) is an important cereal crop that is cultivated globally. In storage, maize is infested by the maize weevil (Sitophilus zeamais Motchulsky). In sub-Saharan Africa where maize is an important staple crop, infestation by S. zeamais is severe. Chemical pesticides have been the key pest management tools for this pest but these practices come with consequences such as insect resistance to pesticides, food and environmental contamination, and depletion of non-target species. These challenges associated with use of chemical pesticides may be overcome by controlling this pest with natural enemies such as entomopathogens. In the laboratory, this study evaluated the pathogenicity of six entomopathogenic nematodes (EPN) - Heterorhabditis bacteriophora Poinar (Lewiston, and Oswego strains); H. indica Poinar, Karunakar, and David (Homl strain), H. georgiana (K22), Steinernema feltiae (SN), and S. carpocapsae (All), and two fungi namely, Beauveria bassiana (GHA) and Metarhizium brunneum (F52) to adult weevils (S. zeamais). All nematodes used in the study were pathogenic to adult weevils. However, S. carpocapsae was the most virulent to the adult weevils. High doses (1 x 10(9) conidia/mL) of the fungi application caused significant weevil mortality compared to the control. Subsequently, in a novel approach, this study established the basis for effective storage of maize by treating storage bags (jute bags) with wettable powder of B. bassiana (2.13 x 10(7) conidia/mm(2)) and then exposing adult weevils to the treated jute bags. The results showed that adult weevils that walked for 30 min on the treated jute bags recorded 100% mortality at 14 days post-inoculation. Thus, there is the potential for using a wettable powder of B. bassiana to protect maize from S. zeamais during storage in jute bags.