THIS ARTICLE is incredibly helpful. Check out “Safe Mosquito and Insect Repellent for Dogs and Cats.” From the article (the intro and bullet points of topics covered):
“Furry haircoats help somewhat, but dogs and cats get bitten by mosquitoes, flies and other insects just like we do. Biting insects are not only bothersome; they may transmit deadly diseases such as heartworm and West Nile Virus. …