Infochemical terminology: based on cost-benefit analysis rather than origin of compounds?

The involvement of chemicals in interactions between individual organisms has been recognized for many years. The current terminology of these so-called semiochemicals developed over a 25 year period and the definition of each category was proposed in a specific context. As a result, the definitions of the various categories are heterogeneous. The present definition of semiochemicals (Nordlund & Lewis, 1976) includes toxins and nutrients. We distinguish between (a) toxins and nutrients, which are themselves to the benefit or detriment to the interacting organisms and (b) information conveying chemicals (infochemicals). Through the response they elicit these latter chemicals are to the benefit or detriment of the receiving organism. Toxins and nutrients may also convey information. If so, we propose to refer to these chemicals as toxin or nutrient when poisonous or nutritious aspects are considered and as infochemical when their role as information carrier is considered. Semiochemical terminology according to Nordlund & Lewis (1976) is based to a large extent on the origin of the compounds in specific interactions. Only those interactions are regarded where one of the interactants is the producer or emitter of the chemical. However, if an infochemical plays a role in the interaction between two individuals, it is by no means certain that either of the two is the actual producer or emitter. The producer or emitter may be a different organism from the same or even from another trophic level but is clearly associated to at least one of the interactants. Arguments are given to eliminate the origin criterion from the terminology and to use the cost-benefit criterion as the sole determinant of infochemical subdivisions.