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Natural variation in virulence of the entomopathogenic fungus Beauveria bassiana against malaria mosquitoes.

Valero-Jiménez CA, Debets AJ, van Kan JA, Schoustra SE, Takken W, Zwaan BJ, Koenraadt CJ - Malar. J. (2014)

Bottom Line: All 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.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.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Genetics, Wageningen University, P,O Box 309, 6700, AH Wageningen, The Netherlands. claudio.valero@wur.nl.

ABSTRACT

Background: Insecticide 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.

Methods: Laboratory 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.

Results: All 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.

Conclusions: This 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.

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Related in: MedlinePlus

Hazard ratios for fungal infection using isolate IMI391510 as a baseline. Dot symbols represent the isolates that were not significantly different from the reference isolate IMI391510. Triangle/square symbols show isolates that were more/less virulent than the reference isolate. Whiskers represent the 95% CIs. 1st or 2nd indicates the result of the first or second biological replicate of an isolate.
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Fig2: Hazard ratios for fungal infection using isolate IMI391510 as a baseline. Dot symbols represent the isolates that were not significantly different from the reference isolate IMI391510. Triangle/square symbols show isolates that were more/less virulent than the reference isolate. Whiskers represent the 95% CIs. 1st or 2nd indicates the result of the first or second biological replicate of an isolate.

Mentions: Hazard ratios (HR) were estimated relative to the mortality pattern of the reference isolate, IMI391510. This isolate was tested in detail during earlier laboratory and field trials [11, 23], and thus constituted a relevant reference point. Virulence was classified in three groups: (1) isolates for which the HR was significantly higher than the HR of the reference isolate (these were termed ‘highly lethal’ (HL)); (2) isolates that were not significantly different compared the reference isolate (these were termed ‘lethal’ (L)); and, (3) fungal isolates that had significantly lower HR than the reference isolate (these were termed ‘slightly lethal’ (SL)). The majority of the 29 isolates was classified as lethal, although at least three were HL isolates and five were SL isolates (Figure 2). Virulence varied widely, as depicted by the extremes: isolate 8028 was on average 3.7 times more virulent and isolate 2861 was on average 2.7 times less virulent than the reference isolate IMI391510. All of these isolates (8028, IMI391510 and 2861) were tested within the same bioassay (Figure 1F) removing any possibility of temporal bias.Figure 2


Natural variation in virulence of the entomopathogenic fungus Beauveria bassiana against malaria mosquitoes.

Valero-Jiménez CA, Debets AJ, van Kan JA, Schoustra SE, Takken W, Zwaan BJ, Koenraadt CJ - Malar. J. (2014)

Hazard ratios for fungal infection using isolate IMI391510 as a baseline. Dot symbols represent the isolates that were not significantly different from the reference isolate IMI391510. Triangle/square symbols show isolates that were more/less virulent than the reference isolate. Whiskers represent the 95% CIs. 1st or 2nd indicates the result of the first or second biological replicate of an isolate.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4364330&req=5

Fig2: Hazard ratios for fungal infection using isolate IMI391510 as a baseline. Dot symbols represent the isolates that were not significantly different from the reference isolate IMI391510. Triangle/square symbols show isolates that were more/less virulent than the reference isolate. Whiskers represent the 95% CIs. 1st or 2nd indicates the result of the first or second biological replicate of an isolate.
Mentions: Hazard ratios (HR) were estimated relative to the mortality pattern of the reference isolate, IMI391510. This isolate was tested in detail during earlier laboratory and field trials [11, 23], and thus constituted a relevant reference point. Virulence was classified in three groups: (1) isolates for which the HR was significantly higher than the HR of the reference isolate (these were termed ‘highly lethal’ (HL)); (2) isolates that were not significantly different compared the reference isolate (these were termed ‘lethal’ (L)); and, (3) fungal isolates that had significantly lower HR than the reference isolate (these were termed ‘slightly lethal’ (SL)). The majority of the 29 isolates was classified as lethal, although at least three were HL isolates and five were SL isolates (Figure 2). Virulence varied widely, as depicted by the extremes: isolate 8028 was on average 3.7 times more virulent and isolate 2861 was on average 2.7 times less virulent than the reference isolate IMI391510. All of these isolates (8028, IMI391510 and 2861) were tested within the same bioassay (Figure 1F) removing any possibility of temporal bias.Figure 2

Bottom Line: All 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.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.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Genetics, Wageningen University, P,O Box 309, 6700, AH Wageningen, The Netherlands. claudio.valero@wur.nl.

ABSTRACT

Background: Insecticide 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.

Methods: Laboratory 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.

Results: All 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.

Conclusions: This 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.

Show MeSH
Related in: MedlinePlus