It's a numbers game. Male mosquitoes are pollinators, so their presence in the environment as far as vectors of disease go is basically nil.
Once a male mates with a female, the females eggs are already fertilized, so the presence of normal male mosquitoes doesn't matter...as long as the genetically modified mosquitoes considerably outnumber the normal male mosquitoes.
Once a male mates with a female, the females eggs are already fertilized, so the presence of normal male mosquitoes doesn't matter...as long as the genetically modified mosquitoes considerably outnumber the normal male mosquitoes.