Apparently you don't need to bother about male mosquitoes, because they're all veggies and, rather poofily, feed off nectar from flowers and don't go looking for human blood like the girls do.
What is this 'frequency of the male mosquito?' Well, it could be the frequency of its wing-beat, but Internet sources estimate this to be, for the male mosquito, only 600-900Hz.
Some Internet sources say the female wing-beat frequency is higher, some say it's lower, but all sources are agreed that it is by the differing frequency of the wing-beat that male and female mosquitoes recognise eachothers' presence.
Having involved myself in researching web-based bollox about mosquitoes, I find a study from the UK-based Cochrane Collaboration, described as a non-profit health research organisation, which reports findings by Ahmadali Enayati, a professor at Mazandaran University of Medical Sciences in Iran, that 'conclusively showed the electronic repellents did not ward off female mosquitoes'.
Well, bugger that. Twelve and a half quid down the khazi.
Incidentally, there are blood-suckers apart from female mosquitoes. On a couple of US websites I find the device I have just bought being flogged for £3.50. BA's price? £12.50.