Entomology was the study of insects. One who specialized in the field was known as an entomologist.
When Cutler thanked T'Pol for allowing her to join the landing party on a Minshara-class planet, T'Pol waved it off as it was a favor, and explained that "You were selected because your specialty is entomology. This planet has a diverse insect population." (ENT: "Strange New World")
Jake Sisko tutored Mardah in entomology in 2370. Nog thought that she was studying "bugs" to learn how to be a chef. (DS9: "Sanctuary", "Playing God")