Universal Journal of Agricultural Research 8(2): 41-45, 2020 http://www.hrpub.org DOI: 10.13189/ujar.2020.080203 Effectiveness of Entomopathogenic Nematodes against the African White Rice Stem Borer Maliarpha separatella Rag Vincent Kega 1,* , Muo Kasina 2 , Florence Olubayo 3 , John Huria Nderitu 3 1 Kenya Agricultural and Livestock Research Organization, Industrial Crops Research Centre, Mwea, Kenya 2 Kenya Agricultural and Livestock Research Organization, National Sericulture Research Centre, Kenya 3 Department of Plant Science and Crop Protection, College of Agriculture and Veterinary Services, University of Nairobi, Kenya Received December 23, 2019; Revised January 30, 2020; Accepted February 7, 2020 Copyright©2020 by authors, all rights reserved. Authors agree that this article remains permanently open access under the terms of the Creative Commons Attribution License 4.0 International License Abstract The efficacy of three entomopathogenic nematodes (EPN) species Steinernema carpocapsae Weiser, Steinernema karii Waturu, Hunt & Reid, Heterorhabdtids indica Poinar, Karunaka & David and two EPN isolates collected from Coastal Kenya (EX MOMBASA) and Rift valley (EX NAKURU) was evaluated against larvae of African white rice stem borer, Maliarpha separatella Rag. The experiment was carried out using no- choice modified filter paper bioassay at KARI-Mwea. Whatman filter paper was substituted with white cotton cloth discs. The activity of the biological agents under study was determined at 25°C and 65% relative humidity, with concentrations of 50, 100 and 200 infective juveniles (IJs) per one M. separatella third instar larva. The larvae were confined in 60mm plastic petri dishes in darkness as the larvae spend their entire life inside the rice stems. The mortality rate was determined at 24, 48, 72 and 96 hours after application of the nematode suspension. Significant virulence was obtained with all the nematode species at 200 infective juveniles (IJs). There was low mortality at 50 and 100 concentration rates. All the EPNs significantly reduced M. separatella larvae after 48 hours in the following order H. indica> EX NAKURU> S. carpocapsae> EX MOMBASA >S. karii. The number of nematodes from the infected cadavers after 48 hours post infection was H. indica (553), EX –MSA (294), EX-NKU (242), S. karii (168) and S. carpocapsae (157). S. karii took the longest time (96 hours) to kill all the test insects. In conclusion, the study shows that EPNs are effective against M. separatella and could be used within an integrated pest management strategy for the pest. There is need to carry out further studies to determine effective dosages under field conditions. Keywords Entomopathogenic Nematodes, Efficacy, African White Rice Stem Borer, Maliarpha separatella 1. Introduction The control of pests and diseases including Maliarpha separatella at Mwea irrigation scheme is through use of pesticides following a calendar based spraying regime developed by Mwea Integrated Agricultural Development Centre (MIAD). However, use of pesticides is associated with various problems. For farmers, the most serious are the acquisition of pest resistance to the chemicals, secondary pest outbreaks, and health hazards associated with the application of chemicals. For consumers, the main problems are pesticide residues in food and environmental degradation [16]. Due to these factors, research towards developing alternative control strategies is warranted and the use of entomopathogenic nematodes (EPNs) in irrigated rice ecologies offers a viable alternative. Most of EPN formulations used in biological control of insect pests are from two Families namely Steinernematidae and Heterorhabditidae in order Rhabtida [1]. The formulations consist of third stage infective juvenile (sometimes referred to as IJ or dauer). It is non-feeding, developmentally arrested and the only EPN life stage that exists outside the host insect. The IJ seeks insect hosts, and after entering, they release an associated mutualistic bacterium, Xenorhabdus for Steinerernematids and Photorhabdus for Heterorhabditids, respectively [1]. The nematode-bacterium complex usually causes host mortality within 24- 48 hours [2]. The nematodes provide shelter to the bacteria, which, in turn, kill the insect host and provide nutrients to the nematode [1]. The bacteria CITE THIS PAPER [1] Vincent Kega , Muo Kasina , Florence Olubayo , John Huria Nderitu , "Effectiveness of Entomopathogenic Nematodes against the African White Rice Stem Borer Maliarpha separatella Rag," Universal Journal of Agricultural Research, Vol. 8, No. 2, pp. 41 - 45, 2020. DOI: 10.13189/ujar.2020.080203.