Abstract
BackgroundInsecticide resistance is greatly hampering current efforts to control malaria and therefore alternative methods are needed. Entomopathogenic fungi have been proposed as an alternative with a special focus on the cosmopolitan species Beauveria bassiana. However, few studies have analysed the effects of natural variation within fungal isolates on mosquito survival, and the implications and possible exploitation for malaria control.MethodsLaboratory bioassays were performed on adult female mosquitoes (Anopheles coluzzii) with spores from 29 isolates of B. bassiana, originating from different parts of the world. In addition, phenotypic characteristics of the fungal isolates such as sporulation, spore size and growth rate were studied to explore their relationship with virulence.ResultsAll tested isolates of B. bassiana killed An. coluzzii mosquitoes, and the rate at which this happened differed significantly among the isolates. The risk of mosquitoes dying was around ten times higher when they were exposed to the most virulent as compared to the least virulent isolate. There was significant variation among isolates in spore size, growth rate and sporulation, but none of these morphological characteristics were correlated, and thus predictive, for the ability of the fungal isolate to kill malaria mosquitoes.ConclusionsThis study shows that there is a wide natural variation in virulence of isolates of B. bassiana, and that selecting an appropriate fungal isolate is highly relevant in killing and thus controlling malaria mosquitoes, particularly if used as part of an integrated vector management strategy. Also, the wide variation observed in virulence offers the opportunity to better understand the molecular and genetic mechanisms that drive this variation and thus to address the potential development of resistance against entomopathogenic fungi.
Highlights
Insecticide resistance is greatly hampering current efforts to control malaria and alternative methods are needed
Production of Beauveria bassiana All isolates of B. bassiana used in this study were obtained from the USDA-ARS Collection of Entomopathogenic Fungal Cultures (ARSEF) (Table 1) except for isolate IMI 391510, which was kindly provided by the Bioprocess Engineering Department (Wageningen University, The Netherlands)
Bioassays on Anopheles coluzzii All B. bassiana isolates tested were pathogenic to An. coluzzii with mortalities of at least 92.5% by day 14 (Figure 1)
Summary
Insecticide resistance is greatly hampering current efforts to control malaria and alternative methods are needed. An effective way to alleviate the burden of malaria is to control its vector (anopheline mosquitoes) using insecticides. This can be achieved either through the use of insecticide-treated bed nets (ITNs) or through indoor residual spraying of Spores of hypocrealean entomopathogenic fungi are able to infect insects, including mosquitoes, via attachment to the insect’s epicuticle [7]. Spores will penetrate the insect’s cuticle by forming a germ tube and appressorium. The latter structure uses mechanical pressure and produces cuticledegrading enzymes for further penetration [8,9]. Sporulation of the fungus takes place a few days later, depending on environmental conditions [10]
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