SENTRY PurrScriptions Plus Squeeze-on is formulated with an adulticide called Etofenprox. When applied monthly, PurrScriptions Plus kills adult fleas, deer ticks and repels mosquitoes, including the mosquito that carries West Nile virus, for up to one month. This product also includes pyriproxyfen, an insect growth regulator that kills flea eggs and larvae for up to three months per application.