Improving the biodiversity of ponds and lakes in malaria-endemic regions could offer a powerful and sustainable way to control malaria.

 

A common mosquito-controlling strategy is to apply biological insecticides, such as Bacillus thuringiensis israelensis (Bti) — a bacterium that produces toxins that target mosquito larvae. Because of this precise impact, Bti treatment preserves more biodiversity than chemicals such as DDT, which are lethal to most species.

 

But Bti breaks down in the environment after a few days, making secondary mosquito outbreaks possible if there are no natural predators or competitors to keep mosquito larvae levels low.

 

Now researchers from two German institutions have shown how diverse communities of mosquito-eating crustaceans — tiny plankton-like creatures from the same family as crabs — can keep the larval populations in check by out-competing them.

 

The authors say their work shows for the first time that crustaceans can be more effective at sustainably suppressing mosquito larval populations than Bti treatment.

 

To carry out the study, the researchers introduced mosquito populations to several artificial ponds at a test site in Leipzig, Germany, containing crustacean communities of varying numbers and species diversity. In each test, the team measured the numbers of mosquito larvae and the stage of their life cycle they had reached over time. After 21 days, they also added Bti to assess its effect on the larvae in the presence of the crustaceans.

 

The research, published in this month's edition of the Journal of Vector Ecology, shows that mosquito populations decreased significantly in the ponds when there was a high diversity of crustaceans. The insects also became as much as ten times more sensitive to the Bti toxin in such ponds. But this effect was hardly detectable in the ponds with the most diverse and fully developed crustacean populations as the number of mosquito larvae was so low.