Plants are not only used as energy and nutrient resources for herbivores. Plants can be ingested because of their activity against host parasites and other pathogens. This so-called medicinal role of plants is well reported in ethnopharmacology and under-reported in wild animals. More studies on wild animals are needed because any plant in the world contains bioactive compounds, and probably all plants, no matter how toxic they are, experience herbivory. For example, we tested the activity of extracts and essential oils from Papaver rhoeas and Echium plantagineum against a selection of laboratory pathogens because Great bustards Otis tarda preferred these plants during the mating season, with male fecal droppings showing a higher frequency of P. rhoeas particles than the fecal droppings of females. We hypothesized that P. rhoeas could be helpful for males in the mating season if any part of this plant harbors bioactivity against parasites and other pathogens. Males’ immune system is weakened during the mating season because of their investment in secondary sexual characters and sexual display. As a first exploration of the bioactivity of these plants, we evaluated extracts of both plants against a sample of laboratory models, including a flagellated protozoon (Trichomonas gallinae), a nematode (Meloidogyne javanica) and a fungus (Aspergillus niger). Non-polar and polar extracts of the aerial parts of P. rhoeas, especially the extracts of flowers and capsules, and the extracts of leaves and flowers of E. plantagineum showed activity against nematodes and trichomonads. The bioactivity of plants against parasites could explain the foraging behavior of stressed animals. The chemical communication underpinning the capacity of fauna to recognize those plants is far less known.

Background: Diets combine food types according to some trade-offs, as for example maximising nutrients and minimising toxins. But some diets include elements because of their activity against the host parasites and other pathogens. This so-called medicinal role of food is under-reported in the literature, either because toxic elements in diets of livestock and wildlife are infrequent, or because their activity against parasites and pathogens has not been fully documented. We contribute to fill this knowledge gap by testing the activity of extracts and essential oils from Papaver rhoeas and Echium plantagineum against a selection of laboratory pathogens. These plants are strongly selected by great bustards Otis tarda during the mating season. Results: During this season we found a significantly higher frequency of P. rhoeas in male than in female faeces. The activity of different extracts of these plants against some laboratory models including a flagellated protozoan (Trichomonas gallinae), a nematode (Meloidogyne javanica) and a fungus (Aspergillus niger) was evaluated. We found activity against nematodes and trichomonads in non-polar and polar extracts of the aerial parts of P. rhoeas, especially the extracts of flowers and capsules, and E. plantagineum, especially the extracts of leaves and flowers.Conclusions: Both plants showed anti-parasitic activity, a result compatible with the hypothesis that great bustards eat plants for non-nutritional purposes, likely to assist them in coping with parasites and other pathogens, and P. rhoeas could be especially helpful for males during the mating season, when their immune system is weakened by the investment in secondary sexual characters and sexual display. The self-medication properties of plants and animals included in diets should be considered in studies of foraging behaviour, habitat selection, and even conservation biology of wildlife.

Arthropods and specifically beetles can synthesize and/or sequester metabolites from dietary sources. In beetle families such as Tenebrionidae and Meloidae, a few studies have reported species with toxic defensive substances and antiparasitic properties that are consumed by birds. Here we have studied the antiparasitic activity of extracts from beetle species present in the habitat of the Great Bustard (Otis tarda) against four pathogen models (Aspergillus niger, Meloidogyne javanica, Hyalomma lusitanicum, and Trichomonas gallinae). The insect species extracted were Tentyria peiroleri, Scaurus uncinus, Blaps lethifera (Tenebrionidae), and Mylabris quadripunctata (Meloidae). M. quadripunctata exhibited potent activity against M. javanica and T. gallinae, while T. peiroleri exhibited moderate antiprotozoal activity. The chemical composition of the insect extracts was studied by gas chromatography coupled with mass spectrometry (GC-MS) analysis. The most abundant compounds in the four beetle extracts were hydrocarbons and fatty acids such as palmitic acid, myristic acid and methyl linoleate, which are characteristic of insect cuticles. The presence of cantharidin (CTD) in the M. quadripunctata meloid and ethyl oleate (EO) in T. peiroleri accounted for the bioactivity of their extracts.