Keynote Lecture “Pyrrolizidine alkaloids – medicine for insects?”

Since toxicity is not a character but an effect of a chemical on a certain organism, it not only depends on the dose but also on the receiver. 1,2-dehydropyrrolizidine ester alkaloids (PAs), although harmful secondary plant chemicals for vertebrate animals including humans, do have beneficial effects for particular, adapted insects. Some actively gather PAs from dead or injured plant tissues by a peculiar behaviour performed independently of, and in addition to feeding: PA-pharmacophagy ([Fig. 1]).

Fig. 1 Self-medicating milkweed butterflies. Males of Tirumala petiverana and Amauris ochlea (Lepidoptera: Nymphalidae: Danainae) taking up pyrrolizidine alkaloids from a wound at an inflorescence of Heliotropium indicum (a) and from a dish containing pure PAs (b) to potentially increase their chances of survival and biological fitness.

This talk will discuss examples of PA-pharmacophagy and their peculiarities. PA-pharmacophagy is not necessary for maintaining life but serves (potentially) to increase chances of survival and/or biological fitness, sometimes also providing such a benefit for sex partners and/or offspring. It is not an insect- plant relationship in the common sense, but an insect-chemical relationship, often shown by one sex only and never continuously engaged, only temporarily. Similar behaviours for taking advantage of natural products not essential for life are also known from other insects (animals).

Are we dealing with self-medication? This term is used for taking chemicals capable of curing an acute pathological situation, preventing a disease, or boosting general well-being. When insects are in focus, insufficient understanding about their state of health, sentience and welfare makes any definition of self-medication challenging. However, behavioural activities that relate to specific chemicals not essential for living and gathered from peculiar sources, are distinct from general activities of the species and performed only temporarily, and serve to enhance chances of survival and/or biological fitness, can surely be regarded as self-medication, too.

Publication History

Article published online:
16 November 2023