Spermless mozzies could help fight Malaria

Releasing spermless male mosquitoes could help reduce outbreaks of malaria, according to a study published this week in the journal PNAS.

Malaria causes over a million deaths every year, 90% of which occur in Sub-Saharan Africa.  It is caused by the microscopic parasite Plasmodium, which is transmitted between human hosts by female Anopheles mosquitoes.  As there is no widely available vaccine, attempts to limit outbreaks in susceptible populations have focussed on controlling the numbers of mosquitoes using insecticides.  These strategies are becoming less successful as mosquitoes develop resistance to the chemicals used.

Researchers from Imperial College London have been investigating ways of reducing the numbers of malarial mosquitoes by hindering their reproduction.  Their work focussed on Anopheles gambiae, the most common vector species in Africa.  Females of this species mate only once in their lifetime, after which they lay a large number of eggs and are no longer receptive to males.

The researchers created sterile male mosquitoes that did not produce sperm by injecting individual embryos with fragments of RNA to silence the zpg gene involved in sperm development.  When mated to these spermless males, females showed the same post-mating behavioural responses as they did with fertile males.  Dr Flaminia Catteruccia from Imperial College London said "These females did not seem to realise they had not received sperm, so they behaved as normal.  They started laying [sterile] eggs and completely switched off their receptivity to further matings."

The mass release of these spermless males could be a good way to control mosquito numbers, and thus reduce malaria transmission, in high-risk areas.  However, there is still much work to be done.  Dr Catteruccia said "Our method is not immediately transferable to the field because the way we target sperm is a laborious process: we have to inject every individual mosquito. In the future there may be more high-throughput techniques, but these have not yet been developed."