Yes, those aphids can be a nuisance at times.
And all it takes is one lone female to come into contact with your plants, either by flight(in their winged stage) or even hitching a ride on your clothing, into your grow area.
But one of the features of female aphids that allows them to reproduce so damn fast is their ability to give live birth, so that they can skip the egg stage.
And also females don't need a male around to fertilize their eggs, a biological reproductive process known as parthenogenesis.
http://en.wikipedia.org/wiki/Parthenogenesis
Aphids can reproduce parthenogenetically, which is basically an asexual reproduction method where a female aphid can give live birth to clones of herself, without any input from a male aphid.
dvg