The mosquito, mankind’s blood-sucking nemesis, has a new enemy: gardening.
Researchers in Mali have discovered that removing the flowers of a common shrub kills off malaria-transmitting mosquitoes by starving them of a vital food source.
The invasive plant Prosopis julifora is native to Central and South America but was introduced to Africa in the 1970s as a way of tackling deforestation. Unfortunately it also provided a major new food source for adult mosquitoes.
So experts from Universities in Mali, Israel and the United States experimented by removing the flowers of the bush to see if it would cut local mosquito numbers.
They studied nine villages: six where the flowering shrub was in abundance and three where it didn’t grow at all.
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In three of the shrub-invaded villages they chopped off the flowers. By monitoring the number of mosquitoes caught in traps in the villages they found that ‘gardening’ had reduced their numbers by nearly 60% compared to the villages where the flowers were left alone.
In fact, the number of mature female mosquitoes, the ones that spread malaria, dropped to levels similar to the villages without the shrubs.
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Mature mosquitoes spread malaria to humans by passing on parasites when they bite. Younger mosquitoes in turn become infected when they bite the same human and ingest their parasite-infested blood.
It takes about 10 days for the young infected mosquito to become infectious to humans, which in insect lifespan makes them pretty old - effectively grandmas. And while these aged mosquitoes are partial to a bit of blood, they rely on flower nectar as their main energy source.
The flowers of the Prosopis julifora shrub grow for much longer than those on native plants, meaning mosquitos have a food source for longer too. Take that away and many mosquitos die off.
Although the researchers caution that ‘gardening’ might not be as effective in more lush parts of the world where plant nectar is readily available, Africa has a disproportionately high share of the world’s malaria deaths.
In 2015, the continent was home to 90% of the world’s malaria cases and 92% of malaria deaths.