evidence: It is difficult to protect your dog from mosquitoes, especially if the dog spends much time outside. You can reduce outdoor exposure to mosquitoes by not walking your dog in the early morning or early evening hours. Those are the hours when mosquitoes are most active. Sensitive animals, including puppies, should be housed in closed or screened buildings, and the mosquitoes inside killed with safe insecticide. Imidacloprid is a topical drug that can be used on dogs (but not cats) to repel adult female mosquitoes for up to 4 weeks. Mosquitoes are not attracted to light, so "bug zappers" do not help control mosquitoes; they may actually be harmful because they destroy insects that prey on mosquitoes.