Some Research Goals at El Bosque Nuevo, Costa Rica
Pharmacophagy has been described as the syndrome where insects (animals) search for certain secondary (plant) substances directly, take them up and utilize them for a specific purpose other than primary metabolism or merely host recognition.
Quite well-understood examples for pharmacophagy with respect to pyrrolizidine alkaloids (PAs) are butterflies (Danainae, Ithomiinae) and moths (Arctiidae) but certain Orthoptera (Pyrgomorphidae: Zonocerus), Coleoptera (Chrysomelidae: Gabonia) and Diptera (Chloropidae) also exhibit elaborate associations with PAs. (more)
Pyrrolizidine alkaloids (1,2-dehydropyrrolizidine alkaloids)(PAs) represent a large group of ester alkaloids of diverse structure. They are built by a necin alcohol and a necin acid which form mono- or diesters or macrocyclic diesters and occur in nature (in plants and in insects storing PAs from plants) as N-oxides. In vertebrates, 1,2-dehydropyrrolizidines are metabolized to pyroles which have hepatotoxic and other hazardous effects. PAs are known from about 600 species of plants in the Asteraceae (Eupatorieae, Senecioneae), Apocynaceae, Boraginaceae and Fabaceae, and, so far, about 400 structures have been elucidated. A plant usually produces a mixture of different PAs, and PAs often are unequally distributed within a given plant.
PA-containing plants are – when withered or dry – the sources of PAs for PA-pharmacophagous insects. We not only search for new sources of PAs (PA-containing plants) but study intraindividual distribution and quantitative variation of PAs.
Ctenuchiinae are in the focus of our studies at EBN. We try to identify patterns of their morphological, chemical, and ecological features. Also, we use some as bioindicators for finding new natural sources of PAs.
Aposematism, Batesian and Müllerian Mimicry. Almost all PA-pharmacophagous species are aposematic in appearance (colours, behaviours) and involved in mimicry rings – due to storage of PAs as defensive chemicals. Ctenuchines are members of particularly complex mimicry rings, involving not only other Lepidoptera but Hymenoptera, Diptera and Coleoptera, too. We want to learn details about the mimicry complexes.
Pheromone communication. Males of many PA-pharmacophagous Lepidoptera use PAs as precursors for the biosynthesis of courtship pheromones. Ctenuchines exhibit a particularly great diversity in the structure of androconial organs which are expressed as expandable hair tufts on the wings and legs, as flocculent-producing pouches or as protrudable coremata in the abdomen. We do comparative morphological as well as chemical studies of androconial organs.
Biology of early stages. Better understanding of the biology of the early stages of Ctenuchines and, in particular, their larval hostplants is a crucial element in unravelling the chemoecology of these moths. Aposematism and mimicry is most likely not 'just' due to gathering PAs as adults. Which other defensive chemicals are involved?
Antagonists. Being aposematic and generally unpalatable does not mean that there are no (specialized) predators and/or parasitoids.
Thus, we aim to gain an understanding of the diversity of the ctenuchine community at EBN, in particular the diversity of forms, life-styles, androconia, tymbal organs, pheromones, .... and gather chemoecological data of general relevance for insects associated with PAs.
- search for natural sources of PAs
- do an inventure of the ctenuchine moths at EBN by baiting with PA-plants and pure PAs, also by netting and by light trapping
- do an inventure of hymenopteran, dipteran and coleopteran (co-)mimics
- identify diurnal and nocturnal reproductive activities
- identify sex-bias in PA-pharmacophagy / attraction to light
- study functional morphology, particularly androconial (and tymbal/tympanal) organs, as a basis for behavioural studies and for phylogentic considerations
- identify mimicry relationships, giving particular attention to sympatricity of species
- study chemicals produced by androconial organs (especially PA-derived ones) as a basis for behavioural studies and for phylogentic considerations
- search for larval hostplants of PA-pharmacophagous insects
- to make cultures possible and thus experimental studies on communication, and
- to learn about sequestration of secondary chemicals from hostplants
- develop sustainable rearing methods for particularly beautiful ctenuchine species and eventually market them for butterfly exhibits
Selected references on our studies of Insects and PAs
Boppré M (1999) 'Drug-addicted' insects in Africa. Metamorphosis 10: 3-15. lesen / read
Pharmacophagy and its diverse functional aspects is introduced using examples from studies on relationships between insects and pyrrolizidine alkaloids (PAs) in Africa. Remaining open questions are outlined, emphasizing the overriding need for natural history information from the field on 'PA-insects' and 'PA-plants'.
Häuser CL, Boppré M (1997) Pyrrolizidine alkaloid-related pharmacophagy in neotropical moths. Pp 291-296 in Ulrich H (ed.) Tropical Biodiversity and Systematics. Proc Intern Symp Biodiversity and Systematics in Tropical Ecosystems. D-Bonn: ZFMK. lesen / read
Baiting tests with pure pyrrolizidine alkaloids (PAs) in Costa Rica, French Guiana, and Peru attracted more than 1,000 ctenuchid and arctiid moths representing 98 species. In combination with literature data on the attractivity of dry PA-containing plants, more than 200 moth species pharmacophagous for those substances can be assumed to exist in the neotropics, which is higher than the numbers hitherto recorded from the Old World tropics. The need for more comprehensive surveys in the neotropics for an evolutionary understanding of PA-related pharmacophagy is emphasized.
Boppré M (1997) Pharmacophagy in adult Lepidoptera: the diversity of a syndrome. Pp 285-289 in Ulrich H (ed.) Tropical Biodiversity and Systematics. Proc Intern Symp Biodiversity and Systematics in Tropical Ecosystems. D-Bonn: ZFMK. lesen / read
The multiplicity of facets involved in non nutritional relationships between adult Lepidoptera and plants containing pyrrolizidine alkaloids are briefly discussed, emphasizing aspects of specificity and (specific, individual and temporal) variation and their consequences, e.g., for understanding mechanisms of chemical defence and sexual communication in an evolutionary context.
Boppré M (1990) Lepidoptera and pyrrolizidine alkaloids: exemplification of complexity in chemical ecology. J Chem Ecol 16: 165-185. lesen / read
Pyrrolizidine alkaloids (PAs) are defensive secondary metabolites found in numerous plant groups. Various insects belonging to different orders have special requirements for these compounds and sequester them from such plants for their own defence and often as pheromone precursors. The fitness of these insects depends on PAs and, in some cases, PAs even act as regulators of androconial organ development.
This paper discusses selected behavioural, chemical, physiological, and phylogenetic aspects of insect PA relationships, and raises questions about the complex interactions of the variety of PA-related adaptations as they occur amongst a diverse array of species. Although many superficial similarities are recognized, few generalizations can yet be drawn. However, insect PA relationships not only exemplify basic features of chemical ecology but illustrate a multiplicity of aspects and adaptations which we should expect to find in any thorough study of insect-plant relationship.
Boppré M, Pitkin BP (1988) Attraction of chloropid flies to pyrrolizidine alkaloids (Diptera: Chloropidae). Entomol Gener 13: 81-85. lesen / read
Both sexes of several species of Chloropidae in 4 genera (Melanochaeta, Chlorops, Eutropha, Oscinella) and 2 subfamilies (Chloropinae, Oscinellinae) have been found visiting pyrrolizidine alkaloid (PA)1 baits and ingesting these secondary plant chemicals. Some of the same species have also been observed visiting decaying plants and flowers containing PAs.
Boppré M (1986) Insects pharmacophagously utilizing defensive plant chemicals (pyrrolizidine alkaloids). Naturwissenschaften 73: 17-26. lesen / read
Insects of several orders (mainly Lepidoptera) gather pyrrolizidine alkaloids independent of feeding behaviour. By storing these secondary plant metabolites the insects gain protection from predators, and in various species the plant chemicals are used as precursors for the biosythesis of male pheromones; in Creatonotos they even regulate specifically the development of the androconial organs. The variety of aspects involved in this link between chemical defence and sexual communication as well as its consequences are dis¬cussed.
Boppré M, Schneider D (1985) Pyrrolizidine alkaloids quantitatively regulate both scent organ morphogenesis and pheromone biosynthesis in male Creatonotos moths (Lep.: Arctiidae). J Comp Physiol 157: 569-577. lesen / read
Males of Creatonotos gangis and C. transiens possess coremata ('scent organs') of drastically varying sizes (Figs. 2, 3), which release R(-)-hydroxydanaidal (Fig. 1A) in varying amounts. Both the size of the organs and their pheromone content depend on the in¬gestion of pyrrolizidine alkaloids (PAs; Fig. 1 B, C) by the larvae. There is a direct correlation between amounts of PAs ingested and and the size of the organs (Fig. 4). It is the absolute amount of PAs ingested which determines the expression of corematal size, structurally different PAs have identical effects (Table 2); PAs are no essential dietary factors for the general development of the moths (Table 1), and the morphogenetic effect is restricted to the coremata. The findings are discussed in terms of developmental, ecological and functional aspects.
Boppré M (1984) Redefining "pharmacophagy". J Chem Ecol 10: 1151-1154. lesen / read
Boppré M (1981) Adult Lepidoptera "feeding" at withered Heliotropium plants (Boraginaceae) in East Africa. Ecol Entomol 6: 449-452.
Boppré M (1978) Chemical communication, plant relationships, and mimicry in the evolution of danaid butterflies. Entomol exp appl 24: 264-277. lesen / read
The knowledge on pheromone biology in danaid butterflies, on relations between adult danaids and pyrrolizidine alkaloid-containing plants, and on relations between danaid larvae and cardiac glycoside-containing foodplants is briefly reviewed and hypotheses on the phylogenetic origin and development of these penomena are discussed.