Missing Mosquitoes

Tanzanian mosquito populations are declining, and scientists don’t know why.

Jef Akst
Jef Akst

Jef Akst is managing editor of The Scientist, where she started as an intern in 2009 after receiving a master’s degree from Indiana University in April 2009 studying the mating behavior of seahorses.

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Aug 29, 2011

WIKIMEDIA COMMONS, CDC

Parts of Africa are seeing an unexplained and dramatic drop in mosquito populations, according to a paper published last month in Malaria Journal. Coincidently, malaria also seems to be on the decline, with reports from Tanzania, Eritrea, Rwanda, Kenya and Zambia all pointing to significant decreases in disease incidence, reports BBC News. At least part of this is likely due to control measures, such as bed nets treated with insecticides, but the new data suggest that other factors may be at play.

For the last decade, Danish and Tanzanian scientists have been monitoring mosquito populations in Tanzania. In 2009, they caught just 14 Anopheles mosquitoes in 2,368 traps, down from more than 5,000 in 2004. And these particular data came from villages that weren’t using bed nets.

The scientists suggest the dwindling mosquito populations may be due to the changing rainfall patterns, which could disrupt...

Without knowing the cause of the decline, it’s impossible to say whether the mosquito populations will rebound, and if so, when. If they do, there is concern for the children who have not been exposed to the parasite as a result of the decline in mosquitos, and thus have not acquired natural immunity due to exposure. "If the mosquito population starts coming up again, and my own assumption is that it will, it is most likely we will have an epidemic of malaria with a higher level of disease and mortality especially amongst these children who have not been exposed," Meyrowitsch told the BBC.

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