Chemical strategies of social parasites

Dead Acromyrmex queen
An Acromyrmex host queen that tried to walk into a foreign leaf-cutting ant colony was ripped apart by host workers

Social parasites enter social insect colonies and harm their fitness. In case of the leaf-cutting ant parasite Acromyrmex insinuator, the host is essentially castrated. Of course the host colonies try to avoid this type of fate. Their nestmate recognition systems are sensitive enough to detect and reject most intruders (see the image for what happens to an intruding queen). Insects mostly communicate via chemicals, and nestmate recognition is using a chemical blend that is as specific to their colony as a coloured football jersey is to a team.

Social parasites, in turn, often evolved chemical adaptations to bypass host nestmate recognition. One of these adaptations is “chemical camouflage”, where parasites use host chemical substances to “dress” just as host workers, which then take the parasites for one of their own.

Another strategy, termed “chemical insignificance”, consists in parasites not bearing any relevant chemicals: if you met someone without a jersey, you wouldn’t know which team he is on either.

Even though the two strategies have previously been proposed to work in synergy (Bagnères et al 1996 Science 272:889–892; Lenoir et al 2001 Annu Rev Entomol 46:573–599)⁠, they are typically considered separately and researchers try to find out which of the two strategies a parasite uses. In our experiments with Acromyrmex insinuator, we found evidence for both strategies. I think this actually makes a lot of sense and I would expect the two strategies to be synergistic: If you want to dress up as a member of another team, it would be wise not to wear your own jersey under that of the other team because it would look odd and you own jersey may still be spotted. It could be similar for Acromyrmex insinuator parasites: they don’t produce any recognition-relevant substances themselves, so they have it easy to acquire their host-specific nest odour without any interference of a non-fitting odour.

Nehring V, Dani FR, Turillazzi S, et al (2015) Integration strategies of a leaf-cutting ant social parasite. Anim Behav 108:55–65. doi: 10.1016/j.anbehav.2015.07.009

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