PYRROLIZIDINE ALKALOIDS - DIFFERENT ACQUISITION AND USE PATTERNS IN APOCYNACEAE AND SOLANACEAE FEEDING ITHOMIINE BUTTERFLIES (LEPIDOPTERA, NYMPHALIDAE)

Pyrrolizidine alkaloids (PAs) often serve as chemical mediators of pla nt-herbivore-predator interactions. Butterflies (Danainae and Ithomiin ae) and moths (Arctiidae) usually acquire PAs from plant sources (lava l host plants, flowers or withered leaves visited by adults - pharmaco phagy) and thereby become chemically protected against predators; they also use PAs as pheromone precursors. Study by GC-MS of PAs in three species of Ithomiinae butterflies, their larval host plants and adult alkaloid sources showed three different acquisition patterns: (1) larv ae of the primitive Tithorea harmonia sequester PAs from their food pl ant Prestonia acutifolia (Apocynaceae: Echitoideae), and adults may al so acquire these alkaloids from plant sources; (2) larvae of the more derived Aeria olena feed on Prestonia coalita, in whose leaves no PAs were detected. but freshly emerged adults sometimes contain PAs and ma les intensively seek and sequester these alkaloids in plant sources; a nd (3) larvae of the still more advanced Mechanitis polymnia feed on s everal PA-free Solanum species, and adult males sequester the alkaloid s from various plant sources. Males and females of all three species c ontain mostly two PAs, the diastereoisomeric retronecine monoesters ly copsamine and intermedine, stored in the N-oxide form. Larval host pla nts and adult plant sources showed a large array of PA structures, the most abundant and frequent being lycopsamine and its diastereoisomers intermedine, echinatine, rinderine and indicine, and the deoxy-analog ues supinine and amabiline. Bioassays with wild caught and freshly eme rged adults suggest that protection against predation by the orb weavi ng spider Nephila clavipes may be dependent on PA concentration and ma ybe some spider idiosyncrasies, but freshly emerged Aeria olena withou t PAs are also liberated by Nephila, suggesting other protective compo unds. The role of this spider as a selective pressure for PA acquisiti on by ithomiines is not clear. (C) 1996 The Linnean Society of London