PYRROLIZIDINE ALKALOIDS IN THE ARCTIID MOTH HYALURGA-SYMA

The arctiid moth Hyalurga syma (subfamily Pericopinae) sequesters pyrr olizidine alkaloids (PAs) from its larval food plant Heliotropium tran salpinum (Boraginaceae). Colorimetric quantification of total PAs in t he 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. F ood-plant leaves were found to contain the diastereoisomeric retroneci ne esters indicine (IIIa), intermedine (IIIb), and lycopsamine (IIIc), and the heliotridine ester rinderine (IIId) only as minor constituent s, whereas 3'-acetylrinderine (IVc) (68% of total PAs) and the respect ive 3'-acetyl esters of indicine (IVa) and intermedine (IVb) (both 17% ) were the major alkaloids. Supinine (IIa) is detectable in traces onl y. The PA mixtures in eggs, larvae, pupae, and imagines of Hyalurga we re identical: indicine, intermedine, and lycopsamine accompanied by co nsiderable amounts of supinine and amabiline or coromandalinine (IIb/I Ic) were the major components. Only larvae were found to store small q uantities of a 3'-acetyl derivative. Rinderine and its 3'-acetyl ester were never found in the insects. Low concentrations of the arctiid-sp ecific PA callimorphine (I) were present in larvae, pupae, and imagine s. 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 respec tive retronecine esters cannot be excluded. Some trials with the orb-w eaving 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.