Determining the age of female mosquitoes may be crucial to halting the spread of diseases like malaria

A recent project at The Queensland Institute of Medical Research, Australia found that determining the age of female mosquitoes may be crucial to halting the spread of diseases like malaria that kill 2 million people annually.

The difference between a mosquito living for only 1 week, versus 2 to 3 weeks, means everything when it comes to transmission of pathogens which cause dengue fever, Ross River virus, and malaria. Old or geriatric mosquitoes are the most risky in terms of transmission - young mosquitoes may be infected, but they cannot pass the parasites on to a new host.

"Given the resurgence of diseases such as dengue, not only in northern Australia but throughout tropical areas, scientists need to distinguish between the dangerous and the benign," said QIMR's Leon Hugo, who has completed his PhD thesis on the lifespan of a mosquito.

For many years scientists have sought clues to a mosquito's age from the female mosquito's reproductive system, as it is only the females that bite. Subtle changes to the structure of mosquito ovaries occur over time. By removing these organs and looking at them under a microscope, "mosquito obstetricians" have been able to estimate the age of individual mosquitoes. However,removing mosquito ovaries to observe these structural features is a painstakingly delicate process, and few entomologists can do it.

Leon and his collaborators at UQ have developed biochemical-based methods as practical solutions to the problem. First, they measured the quantity of certain chemicals in the exoskeleton or skin of mosquitoes, and found that some of these increase or decrease with age. Based on promising results from previous studies involving the mosquito's cousin, the fruit fly, they also investigated the activity of certain mosquito genes as markers of age. Leon has applied these methods to the dengue mosquito, and a malaria mosquito common throughout Australasia, and scientists can now discriminate between young mosquitoes, and the old risky ones.

With global warming increasing the range of mosquitoes, and the fact that vaccines for dengue and malaria are years away, innovative and practical approaches to disease prevention are essential right now. Leon's work will be used directly in new mosquito control approaches, like introducing life-shortening mosquito parasites, or more broadly to describe the risk of epidemics.