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First report of the infection of insecticide-resistant malaria vector mosquitoes with an entomopathogenic fungus under field conditions.

Howard AF, N'Guessan R, Koenraadt CJ, Asidi A, Farenhorst M, Akogbéto M, Knols BG, Takken W - Malar. J. (2011)

Bottom Line: The results show that B. bassiana infection caused significantly increased mortality with the daily risk of dying being increased by 2.5 × for the fungus-exposed mosquitoes compared to the control mosquitoes.However, the virulence of the B. bassiana conidia decreased with increasing time spent exposed to the field conditions, the older the treatment on the net, the lower the fungus-induced mortality rate.This work shows promise for the use of B. bassiana fungal conidia against insecticide-resistant mosquitoes in the field, but further work is required to examine the role of environmental conditions on fungal virulence and viability with a view to eventually making the fungal conidia delivery system more able to withstand the ambient African climate.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratory of Entomology, Wageningen University and Research Centre, P.O. Box 8031, 6700 EH Wageningen, The Netherlands. afv.howard@gmail.com

ABSTRACT

Background: Insecticide-resistant mosquitoes are compromising the ability of current mosquito control tools to control malaria vectors. A proposed new approach for mosquito control is to use entomopathogenic fungi. These fungi have been shown to be lethal to both insecticide-susceptible and insecticide-resistant mosquitoes under laboratory conditions. The goal of this study was to see whether entomopathogenic fungi could be used to infect insecticide-resistant malaria vectors under field conditions, and to see whether the virulence and viability of the fungal conidia decreased after exposure to ambient African field conditions.

Methods: This study used the fungus Beauveria bassiana to infect the insecticide-resistant malaria vector Anopheles gambiae s.s (Diptera: Culicidae) VKPER laboratory colony strain. Fungal conidia were applied to polyester netting and kept under West African field conditions for varying periods of time. The virulence of the fungal-treated netting was tested 1, 3 and 5 days after net application by exposing An. gambiae s.s. VKPER mosquitoes in WHO cone bioassays carried out under field conditions. In addition, the viability of B. bassiana conidia was measured after up to 20 days exposure to field conditions.

Results: The results show that B. bassiana infection caused significantly increased mortality with the daily risk of dying being increased by 2.5 × for the fungus-exposed mosquitoes compared to the control mosquitoes. However, the virulence of the B. bassiana conidia decreased with increasing time spent exposed to the field conditions, the older the treatment on the net, the lower the fungus-induced mortality rate. This is likely to be due to the climate because laboratory trials found no such decline within the same trial time period. Conidial viability also decreased with increasing exposure to the net and natural abiotic environmental conditions. After 20 days field exposure the conidial viability was 30%, but the viability of control conidia not exposed to the net or field conditions was 79%.

Conclusions: This work shows promise for the use of B. bassiana fungal conidia against insecticide-resistant mosquitoes in the field, but further work is required to examine the role of environmental conditions on fungal virulence and viability with a view to eventually making the fungal conidia delivery system more able to withstand the ambient African climate.

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Survival of Anopheles gambiae s.s. VKPER exposed in WHO cone bioassays to B. bassiana-treated netting. Lines represent netting left in field conditions for 1 (solid black), 3 (solid grey) and 5 (dashed black) days before testing. Mean cumulative proportional survival (±SEM) for control-exposed mosquitoes (open circles) is compared to B. bassiana-exposed mosquitoes (solid squares).
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Figure 3: Survival of Anopheles gambiae s.s. VKPER exposed in WHO cone bioassays to B. bassiana-treated netting. Lines represent netting left in field conditions for 1 (solid black), 3 (solid grey) and 5 (dashed black) days before testing. Mean cumulative proportional survival (±SEM) for control-exposed mosquitoes (open circles) is compared to B. bassiana-exposed mosquitoes (solid squares).

Mentions: The mean (±SE) temperature and humidity during the bioassay exposure periods were 29.2°C (±0.44) and 90.6%RH (±1.52), with ranges of 27.2-32.1°C and 78->95%RH respectively. Confirming previous results from the laboratory [10,11], B. bassiana was pathogenic to An. gambiae s.s. VKPER strain mosquitoes when exposed under field conditions (Figure 3). Significantly increased mortality for the B. bassiana-exposed mosquitoes (when compared to the control mosquitoes) was seen when the treatment on the nets was 1, 3 and 5 days old (Table 1). Despite being significantly different from the control for all the time points, the virulence of the B. bassiana-treated net held in field conditions significantly reduced with increased time in the field; mosquito mortality caused by the one day old fungal treatment on the net was significantly higher than the mortality caused by the 3-day old (HR = 1.33, p = 0.013) and 5-day old fungal treatments (HR = 1.49, p < 0.001). These results indicate a drop off of effectiveness with increasing time the fungal conidia spend exposed to ambient field conditions even over this relatively short trial period.


First report of the infection of insecticide-resistant malaria vector mosquitoes with an entomopathogenic fungus under field conditions.

Howard AF, N'Guessan R, Koenraadt CJ, Asidi A, Farenhorst M, Akogbéto M, Knols BG, Takken W - Malar. J. (2011)

Survival of Anopheles gambiae s.s. VKPER exposed in WHO cone bioassays to B. bassiana-treated netting. Lines represent netting left in field conditions for 1 (solid black), 3 (solid grey) and 5 (dashed black) days before testing. Mean cumulative proportional survival (±SEM) for control-exposed mosquitoes (open circles) is compared to B. bassiana-exposed mosquitoes (solid squares).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3045381&req=5

Figure 3: Survival of Anopheles gambiae s.s. VKPER exposed in WHO cone bioassays to B. bassiana-treated netting. Lines represent netting left in field conditions for 1 (solid black), 3 (solid grey) and 5 (dashed black) days before testing. Mean cumulative proportional survival (±SEM) for control-exposed mosquitoes (open circles) is compared to B. bassiana-exposed mosquitoes (solid squares).
Mentions: The mean (±SE) temperature and humidity during the bioassay exposure periods were 29.2°C (±0.44) and 90.6%RH (±1.52), with ranges of 27.2-32.1°C and 78->95%RH respectively. Confirming previous results from the laboratory [10,11], B. bassiana was pathogenic to An. gambiae s.s. VKPER strain mosquitoes when exposed under field conditions (Figure 3). Significantly increased mortality for the B. bassiana-exposed mosquitoes (when compared to the control mosquitoes) was seen when the treatment on the nets was 1, 3 and 5 days old (Table 1). Despite being significantly different from the control for all the time points, the virulence of the B. bassiana-treated net held in field conditions significantly reduced with increased time in the field; mosquito mortality caused by the one day old fungal treatment on the net was significantly higher than the mortality caused by the 3-day old (HR = 1.33, p = 0.013) and 5-day old fungal treatments (HR = 1.49, p < 0.001). These results indicate a drop off of effectiveness with increasing time the fungal conidia spend exposed to ambient field conditions even over this relatively short trial period.

Bottom Line: The results show that B. bassiana infection caused significantly increased mortality with the daily risk of dying being increased by 2.5 × for the fungus-exposed mosquitoes compared to the control mosquitoes.However, the virulence of the B. bassiana conidia decreased with increasing time spent exposed to the field conditions, the older the treatment on the net, the lower the fungus-induced mortality rate.This work shows promise for the use of B. bassiana fungal conidia against insecticide-resistant mosquitoes in the field, but further work is required to examine the role of environmental conditions on fungal virulence and viability with a view to eventually making the fungal conidia delivery system more able to withstand the ambient African climate.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratory of Entomology, Wageningen University and Research Centre, P.O. Box 8031, 6700 EH Wageningen, The Netherlands. afv.howard@gmail.com

ABSTRACT

Background: Insecticide-resistant mosquitoes are compromising the ability of current mosquito control tools to control malaria vectors. A proposed new approach for mosquito control is to use entomopathogenic fungi. These fungi have been shown to be lethal to both insecticide-susceptible and insecticide-resistant mosquitoes under laboratory conditions. The goal of this study was to see whether entomopathogenic fungi could be used to infect insecticide-resistant malaria vectors under field conditions, and to see whether the virulence and viability of the fungal conidia decreased after exposure to ambient African field conditions.

Methods: This study used the fungus Beauveria bassiana to infect the insecticide-resistant malaria vector Anopheles gambiae s.s (Diptera: Culicidae) VKPER laboratory colony strain. Fungal conidia were applied to polyester netting and kept under West African field conditions for varying periods of time. The virulence of the fungal-treated netting was tested 1, 3 and 5 days after net application by exposing An. gambiae s.s. VKPER mosquitoes in WHO cone bioassays carried out under field conditions. In addition, the viability of B. bassiana conidia was measured after up to 20 days exposure to field conditions.

Results: The results show that B. bassiana infection caused significantly increased mortality with the daily risk of dying being increased by 2.5 × for the fungus-exposed mosquitoes compared to the control mosquitoes. However, the virulence of the B. bassiana conidia decreased with increasing time spent exposed to the field conditions, the older the treatment on the net, the lower the fungus-induced mortality rate. This is likely to be due to the climate because laboratory trials found no such decline within the same trial time period. Conidial viability also decreased with increasing exposure to the net and natural abiotic environmental conditions. After 20 days field exposure the conidial viability was 30%, but the viability of control conidia not exposed to the net or field conditions was 79%.

Conclusions: This work shows promise for the use of B. bassiana fungal conidia against insecticide-resistant mosquitoes in the field, but further work is required to examine the role of environmental conditions on fungal virulence and viability with a view to eventually making the fungal conidia delivery system more able to withstand the ambient African climate.

Show MeSH
Related in: MedlinePlus