ENTOMOPATHOGENIC BACTERIA: XENORHABDUS SPP AND PHOTORHABDUS SPP FROM STEINERNEMA KARII AND HETERORHABDITIS INDICA FOR THE CONTROL OF MOSQUITO LARVAE
Keywords:Entomopathogenic nematodes, Xenorhabdus, Steinernema karii, Photorhabdus, Heterohabditis indica, biocontrol, mosquito larvae
Mosquitoes are vectors of multiple diseases of man through transmission of various pathogens. Malaria, caused by Plasmodium,results in over 429,000 deaths annually. Primary methods of mosquito control are demanding, both economically and logistically, necessitating exploration of bio-control agents that are specific, safe, sustainable and easy to produce. The search for and use of entomopathogenic bacteria could have a significant impact on mosquito control. The objective of this study was to determine the virulence of entomopathogenic bacteria Xenorhabdus spp and Photorhabdus spp, isolated from two entomopathogenic nematodes (EPNs) strains Steinernema karii and Heterorhabditis indica respectively, against mosquito larvae. Mosquito larvae were collected from set up breeding vessels and maintained in distilled water in the laboratory. Bacterial symbiots from S. karii and H. indica were isolated and streaked on MacConkey and NBTA plates. Pure colonies of S. karii’s Photorhabdus spp and H. indica’s Xenorhabdus spp were obtained and characterization done through colony and cell morphological observation, biochemical and bioluminescence tests, and are preserved in the Jomo Kenyatta University of Agriculture and Technology laboratory. The pure cultures were multiplied in LB medium. Treatment concentrations were prepared from cells plus metabolites (cells/ml), cells-only (cells/ml) and metabolites-only (serial dilutions) for each of the bacterium and a combination of both. Ten 4th instar mosquito larvae were treated with each of the concentration. Highest mortality for each category of treatment; cells-only (70%), metabolites-only (100%) and cells plus metabolites (95%), was achieved by using both bacteria. Within 48 hours, all metabolites-only treatments achieved 50% mortality. There was a significant difference between the various treatments and the mosquito larvae mortality rate (ANOVA; F=11.76, df=2; P=0.000038). To our knowledge, this is the first time that cells, metabolites and combination of both from Photorhabdus spp, Xenorhabdus spp and both bacteria has been evaluated against mosquito larvae. These bacteria have shown effective virulence thus potential application as an alternative to primary methods of mosquito control in the fight against malaria.