Fast acting. Long lasting. 3 Monthly treatments. Kills fleas, ticks and mosquitoes plus flea eggs. Hartz Advanced Care 4 in 1 Flea & Tick Drops Plus+ For Dogs and Puppies Weighing 31 to 45 lbs. contains 2 special ingredients. The first ingredient, Phenothrin, is specifically designed to kill adult fleas, ticks and mosquitoes. The second ingredient, (S)-Methoprene, is designed to kill flea eggs and larvae. This combination provides your pet with complete protection. Why is it important to kill flea eggs and larvae? Fleas spend virtually all their life on your pet and they produce a vast number of eggs, which drop off the pet and develop in the environment. Once you see fleas on your pet, there is already an infestation of pre-adult flea stages in your home. Hartz Advanced Care 4 in 1 Flea & Tick Drops Plus+ For Dogs and Puppies Weighing 31 to 45 lbs. is specifically designed to kill adult fleas, flea eggs and larvae, thereby breaking the flea life cycle and making your pet flea free.