Do male Aedes mosquitoes bite?
Some residents have been alarmed by large swarms of mosquitoes at Project Wolbachia sites, with others reportedly experiencing an increase in mosquito bites.
Project Wolbachia, which has been rolled out at 13 sites islandwide, involves releasing male mosquitoes infected with the Wolbachia bacteria to control the population of female Aedes aegypti mosquitoes, which spread dengue.
When the male Wolbachia-carrying Aedes aegypti mosquitoes mate with urban female Aedes aegypti mosquitoes that do not carry Wolbachia, their resulting eggs do not hatch.
The Straits Times looks at reasons behind a rise in bites and debunks some common misunderstandings.
Q: What are some possible reasons behind more mosquito bites at Project Wolbachia release sites?
A: Associate Professor Alex Cook from the National University of Singapore's Saw Swee Hock School of Public Health said the higher biting rate could be perceived, rather than actual - much like when someone talks about head lice, one's scalp may start to itch.
"Following a release, male mosquitoes may be visible, therefore triggering thoughts about mosquitoes, so that when a mosquito does bite, it is remembered and mentally associated with the release," he added.
Dr Ruklanthi de Alwis, deputy director of the Centre for Outbreak Preparedness at Duke-NUS Medical School, said the increasing number of mosquito bites is unlikely to be due to Project Wolbachia. The project reduces only Aedes aegypti mosquito populations, while Singapore has other species that bite people.
These include Aedes albopictus, Culex quinquefasciatus and some Anopheles species.
"It is possible that the current heat, humidity and rain may have resulted in increases in these other mosquito populations," added Dr de Alwis, who is also an assistant professor with Duke-NUS' Emerging Infectious Diseases Programme.
Q: Do male Aedes aegypti mosquitoes bite?
A: No, they do not. According to the National Environment Agency website, these mosquitoes, regardless of whether or not they carry the Wolbachia bacteria, feed only on plant juices such as nectar for survival and energy.
The female Aedes mosquito bites in order to get protein for her eggs, said Prof Cook.
"This is why the lab-grown mosquitoes for release are checked for their sex before release: explicitly to avoid releasing a mosquito that bites someone. While the sexing process is not completely perfect, its accuracy is nevertheless astonishing," he added.
Q: Aside from the Aedes aegypti mosquitoes, do other mosquito species cause dengue?
A: Among the range of mosquito species that Singapore is home to, only the Aedes albopictus species is also known to spread dengue, said Prof Cook.
"It has a rather different ecology to the Aedes aegypti species... the Aedes aegypti species is anthropophilic (has a preference for human habitats) and is frequently found around our homes and in built-up areas, whereas the Aedes albopictus is a nature lover that is more common in forests, parks and low-rise areas. We do find them around homes, but not at the levels of the Aedes aegypti," he said.