What type of hormones signal responses between different organisms?

Pheromones are chemical signals produced by one organism that can influence the behavior or physiology of another organism of the same species. These substances are typically released into the environment and can affect a variety of behaviors such as mating, foraging, and territory establishment. Pheromones play a crucial role in communication between organisms, especially in social insects like ants and bees, where they can signal alarm or recruitment.

While endocrine hormones are responsible for communication within an organism's body, and neurotransmitters function in transmitting signals between nerve cells, they do not facilitate inter-organism communication in the same manner as pheromones. Cytokines primarily act within the immune system to modulate responses among cells, which also does not represent the inter-organism signaling characteristic of pheromones. Thus, it is the unique function of pheromones that makes them the correct answer to the question regarding signaling responses between different organisms.