Anopheles gambiae mosquitoes are the main transmitters of malaria, which affects around 200 million people every year. The females mate only once during their lives.
They store the sperm from this single mating in an organ called the spermatheca, from which they repeatedly take sperm over the course of their lifetime to fertilise the eggs that they lay. The female needs the sperm to stay healthy whilst they are in storage in the spermatheca, so that they are viable each time she uses them to reproduce.
The new research shows that the sperm are partly protected by the actions of an enzyme called HPX15. When the researchers interfered with HPX15 in female A gambiae mosquitoes in the laboratory, the females fertilised fewer eggs and therefore produced fewer offspring. This is the first time that scientists have discovered a mechanism that preserves the function of sperm in A gambiae.
The researchers, from Harvard School of Public Health, the University of Perugia and Imperial College London, believe that their insight could ultimately lead to a new weapon in the fight against malaria. This would work by disabling HPX15 to reduce female fertility and through that, reduce the number of malaria-carrying mosquitoes in circulation.
“Malaria kills over 650,000 people every year and we need to find new ways of tackling it, partly because mosquitoes continue to evolve ways of resisting our efforts,” Dr Robert Shaw, one of the lead authors of the research, said. “We are interested in cutting the numbers of malarial mosquitoes by impairing their ability to reproduce, and our new study suggests a way that we might be able to do this.
“There is no single magic bullet for tackling malaria, but making mosquitoes less fertile could provide us with a valuable weapon against the disease,” said Shaw. The study suggests that HPX15 may protect the stored sperm against potentially damaging molecules called free radicals, which are particularly abundant after a female takes a blood feed.
Ensuring that the sperm are healthy after blood-feeding is important for the female’s fertility as she reproduces after each feed, fertilising her eggs with sperm released from the spermatheca. The study was published in the journal Proceedings of the National Academy of Sciences.