Contraptions that claim to repel mosquitoes by bombarding them with high-pitched frequencies don't work, a new international study suggests.

'There was no evidence in the field studies to support any repelling effects of EMRs hence no evidence to support their promotion or use.'—Ahmadali Enayati, researcher

The researchers tested manufacturers' claims that electronic mosquito repellents (EMRs) repel female mosquitoes and accordingly protect people from bites and disease such as malaria and West Nile virus.

The study — released online Wednesdayby the U.K.-basedCochrane Collaboration, a non-profithealth research organization— details the findings of 10 field studies conducted in different regions around the globe with various species of mosquitoes.

Lead researcher Ahmadali Enayati, a professor at Mazandaran University of Medical Sciences in Iran, said the studies conclusively showed the electronic repellents did not ward off female mosquitoes.

Female mosquitoes feed on human blood to produce their eggs while male mosquitoes feed on nectar from flowers.

"There was no evidence in the field studies to support any repelling effects of EMRs, hence no evidence to support their promotion or use," he said in the study.

The study alsosaid that in 12 of the 15 experiments, the landing rates of mosquitoes on subjects was in fact higher than in control groups.

The authors suggested that EMRs may be ineffectivebecause female mosquitoes can't hear very well, according toother studies.