PYRROLIZIDINE ALKALOIDS IN THE ARCTIID MOTH HYALURGA-SYMA

The arctiid moth Hyalurga syma (subfamily Pericopinae) sequesters pyrrolizidine alkaloids (PAs) from its larval food plant Heliotropium transalpinum (Boraginaceae). Colorimetric quantification of total PAs in the larvae, pupae, and adults of Hyalurga revealed mean values of about 286-445 mug per individual (1.4-2.6% of dry weight). The PA mixtures found in the moth and its larval food plant were evaluated by GC-MS. Food-plant leaves were found to contain the diastereoisomeric retronecine esters indicine (IIIa), intermedine (IIIb), and lycopsamine (IIIc), and the heliotridine ester rinderine (IIId) only as minor constituents, whereas 3'-acetylrinderine (IVc) (68% of total PAs) and the respective 3'-acetyl esters of indicine (IVa) and intermedine (IVb) (both 17%) were the major alkaloids. Supinine (IIa) is detectable in traces only. The PA mixtures in eggs, larvae, pupae, and imagines of Hyalurga were identical: indicine, intermedine, and lycopsamine accompanied by considerable amounts of supinine and amabiline or coromandalinine (IIb/IIc) were the major components. Only larvae were found to store small quantities of a 3'-acetyl derivative. Rinderine and its 3'-acetyl ester were never found in the insects. Low concentrations of the arctiid-specific PA callimorphine (I) were present in larvae, pupae, and imagines. The differences in the PA patterns of the insects and their larval food plant suggest that Hyalurga is capable of modifying plant-derived PAs by inversion of the 7-OH configuration (conversion of the necine base heliotridine into retronecine), and perhaps the inversion of the 3'-OH [conversion of (+)-trachelanthic acid into (-)-viridifloric acid], although the possibility of a selective sequestration of the respective retronecine esters cannot be excluded. Some trials with the orb-weaving spider Nephila clavipes, a common neotropical predator, showed that both freshly emerged and field-caught adults of Hyalurga syma are liberated unharmed by the spider. The liberation could be related to the presence of PAs in the moths.19466967