Farmers’ awareness of bean leaf beetles (Ootheca spp.) and the virulence of Aspergillus flavus and Metarhizium Anisopliae against these pests in Uganda

Abstract

The common bean (Phaseolus vulgaris L.) is a widely grown crop and plays a key role of food and income security in Uganda. However, production of the crop is constrained by field insect pests including bean leaf beetles (BLBs) (Ootheca spp.). The overall objective of the study was to contribute to common bean productivity through controlling BLBs by establishing a strategy involving atoxigenic Aspergillus flavus (L-strain) and Metarhizium anisopliae. A survey to determine farmers’ perceptions and knowledge of BLBs was conducted in 16 sub/counties selected from Arua, Hoima, Lira and Lwengo districts. Bioassays involving A. flavus (L-strain) and M. anisopliae were conducted at the Entomology and Plant Pathology Laboratory at the National Crops Resources Research Institute (NaCRRI), Namulonge, Wakiso, Uganda to determine the virulence of the two entomopathogenic fungi (EPF) on adult BLBs (Ootheca mutabilis S.). Ootheca mutabilis were collected over two cropping seasons in two years in two sub/counties selected from Arua and Lira districts. The study showed that more farmers in Arua and Lira know the local names of BLBs and the major sign of crop damage (holes on leaves) than their counterparts in Hoima and Lwengo districts. Other signs of crop damage like premature senescence and wilting of young plants were least known in the study districts. Farmers in the study districts had limited knowledge on where BLBs come from, where they lay eggs and where they go after beans have been harvested. The current magnitude of bean leaf beetle infestation was ranked as severe in Arua and Lira, moderate in Hoima and minor in Lwengo. The first planting season was reported to experience high populations of BLBs in all the study districts. All farmers in the study districts know alternative host plants for BLBs; however, there is a variety host plants in Arua and Lira compared to Hoima and Lwengo. The use of synthetic insecticides to control BLBs was perceived to be the most effective method for the pests. Delayed sowing was perceived effective and moderately effective, and was mainly practiced in Arua and Lira. The main challenges to bean leaf beetle control were lack of knowledge of the effective control methods for the pests and fake chemicals on market. The bioassays showed that A. flavus (L-strain) and M. anisopliae are equally lethal, and virulent to adults of O. mutabilis (in terms of LC50); however, M. anisopliae has a lower LT50 (2.1 ± 0.4 days) than atoxigenic A. flavus (3.6 ± 0.2 days). The study recommends; promotion of cost-effective practices of controlling BLBs (e.g., crop rotation with non-host crops, and post-harvest tillage), updating of information packages and retooling of extension service providers with relevant information on BLBs, and conducting further studies on the virulence of atoxigenic A. flavus and M. anisopliae involving other developmental stages of O. mutabilis under field conditions.