Self-medication in insects: current evidence and future perspectives

Abstract:
1. Self-medication is an ability to consume or otherwise contact biologically active organic compounds specifically for the purpose of helping to clear a (parasitic) infection or reduce its symptoms. Consumption of these compounds may either take place before the infection is contracted (prophylactic consumption) or after the infection is contracted (therapeutic consumption). 2. An important insight is that self-medication is a form of adaptive plasticity, and as such, consumption of the medicinal substance when uninfected must impose a fitness cost (otherwise the substance would be universally consumed). This distinguishes self-medication from several closely related phenomena such as microbiome effects or compensatory diet choice. 3. A number of recent studies have convincingly demonstrated self-medication within several different, distantly-related, insect taxa. Here I review evidence of self-medication in the wooly bear caterpillar Grammia incorrupta Edwards, the armyworm Spodoptera Guenee, the fruit fly Drosophila melanogaster Meigen, the monarch butterfly Danaus plexippus Kluk, and the honey bee Apis mellifera Linnaeus. 4. These studies show not only that self-medication is possible, but that the target of the medication behaviour may in some cases be kin rather than self. They also reveal very few general patterns. I therefore end by discussing future prospects within the field of insect self-medication.