In areas where malaria mosquitoes have become resistant to chemical pesticides, mosquito-killing fungi can be an effective tool. Fungal spores can effectively infect and kill malaria mosquitoes, even those that are resistant to pesticides. Moreover, the mosquitoes become more susceptible to the pesticides as the fungal infection increases. Researchers from Wageningen University and their colleagues from South Africa have published an article on this effect in the prestigious journal PNAS (Proceedings of the National Academy of Sciences) of this week.
Malaria mosquitoes are becoming increasingly resistant to pesticides. As a result, malaria is difficult to control. Besides the existing chemical pesticides such as DDT and pyrethroids, which are applied indoors and on mosquito nets, there are few options for mosquito control. The use of insect-killing fungi is a novel biological control method for malaria mosquitoes that was developed in 2005 in cooperation with Wageningen researchers. The spores of the fungi can infect mosquitoes upon contact and kill them within several days. Moreover, a fungal infection reduces the mosquito's appetite and slows the development of malaria parasites inside the mosquito.
Together with her colleagues in South Africa, the Wageningen researcher Marit Farenhorst tested these fungi for the first time on various species of pesticide-resistant malaria mosquitoes. In the laboratory in Johannesburg, the research team compared the effectiveness of fungi on mosquitoes that are susceptible to insecticides and their relatives who are resistant. The fungus Beauveria bassiana was able to kill both susceptible and resistant malaria mosquitoes. This indicates that malaria mosquitoes that are resistant to the pesticide are not resistant to the fungus.
In addition, the team studied to what extent mosquitoes that are infected with the fungus are also susceptible to pesticides. To this end, resistant mosquitoes were infected with spores of the fungi Beauveria bassiana or Metarhizium anisopliae. After three days of incubation, they were tested for their resistance to the pesticides permethrin and DDT. Both fungus species increased the mosquitoes' susceptibility to these agents; more mosquitoes died after exposure to the chemicals when they were infected with fungus. The researchers believe that the toxins excreted by the fungi undermine the mosquitoes' resistance mechanism.
Biological mosquito control
The results show the potential of fungi as an effective and sustainable biological control agent for malaria mosquitoes. Due to the increasing problem of pesticide resistance in Africa, they offer a crucial alternative for current control methods.