Ninety percent of the species are female and they supplement their gene pool by mating with members of other species. They achieve this by releasing a retrovirus on nearby planets that infects the host male and begins adjusting his DNA. The host then starts to become Taresian and is drawn to Taresia where he is welcomed and told (incorrectly) that he has always been Taresian and that the species reproduce by implanting Taresian embryos in females of other species. The unsuspecting males are then separated from their shipmates and their every whim is catered for by the women of Taresia. Each male is then married to three females who mate with him. Unfortunately, the amount of DNA removed in the mating will kill the unsuspecting male, hence the Taresians' elaborate deception.
This deception was uncovered by the crew of the USS Voyager in 2373 when Ensign Harry Kim was infected by the Taresian retrovirus. He discovered the body of one of the previous males and escaped the planet.
Because the nearby Nasari disapprove of the Taresian mating process, the Taresians are at war with the Nasari. Despite the Nasari being quite powerful, Taresian ships are quite capable of holding them off. (VOY: "Favorite Son")