A substance transmitted in chemical communication between individuals of different species that benefits the sender or both the sender and receiver (Daly et al. 1998, Jolivet 1998). A chemical substance, produced or acquired by an organism, which, when it contacts an individual of another species in the natural context, evokes in the receiver a behavioural or physiological reaction adaptively favourable to the emitter (Coppel and Mertins 1977). An allelochemic that induces a response in an individual of another species, e.g. an insect, that is beneficial to the emitting organism. Many allomones are essentially defensive, i.e. toxic or repugnant to potential attackers. However, a scent that attracts bees and therefore facilitates pollination is also an allomone (Maxwell and Jennings 1980). See ‘kairomone’, ‘parapheromone’, ‘pheromone’, ‘synomone’, ‘semiochemical’.