terflies, their enthusiasm for these chemi- 

 cals is independent of their nutritional re- 

 quirements. 



Creatonotos moths exhibit some strik- 

 ing similarities to danaine butterflies. 

 Males possess eversible scent organs, 

 called coremata, that emit a dihydropy- 

 rrohzine derived from pyrrolizidine alka- 

 loids, and they, too, stockpile unconverted 

 PAs for protection and transfer them to fe- 

 males. However, there are some basic dif- 

 ferences. Both male and female Creatono- 

 tos feed on PA plants, gathering the 

 protective compounds together with food, 

 and they do so only as larvae (the short- 

 lived adults do not feed at all). So while 

 milkweed butterflies accumulate PAs as 

 adults only, Creatonotos moths hatch with 

 a fixed amount of pheromone and protec- 

 tive chemicals. In both groups, the degree 

 of protection varies from individual to in- 

 dividual, as does the amount of male 

 pheromone. 



The dihydropyrrolizines of many da- 

 naines and Creatonotos are structurally 

 identical, but their roles in influencing the 

 behavior of conspecifics are quite differ- 

 ent. In most butterflies and moths, males 

 expand flieir scent organs only in the final 

 phase of courtship, after the sexes have 

 come together through sight (butterflies) 

 or smell (moths). Creatonotos males, in 

 contrast, display their organs for hours, 

 starting at dawn, whether any females are 

 around or not. The pheromones the males 

 release appear to lure both females and 

 males, leading to the establishment of 

 mating aggregations, or leks. Since Cre- 

 atonotos females also produce phero- 

 mones to lure males (as is typical among 

 moths), the genus appears to use two 

 markedly different means of bringing the 

 sexes together 



We have not yet been able to conduct a 

 detailed field study of these rare, noctur- 

 nal, and quite small moths, but one aspect 

 of their biology has already added a fasci- 

 nating element to the complex story of 

 plant alkaloids and insects. In the field, 

 some Creatonotos individuals have gigan- 

 tic coremata, exceeding the insects' wing- 

 span; others of the same species have 



Male milkweed butterflies and male 

 Creatonotos moths use pyrrolizidine 

 alkaloids for protection and in the 

 synthesis of sex pheromones. The 

 butteifiies emit pheromones from 

 glandular organs known as hairpencils, 

 below. The size of a moth 's scent organs, 

 or coremata, right, depends on the 

 amount of PAs it gathered as a lan'a. 



Photographs by Michael Boppre 



coremata so tiny fliey are almost invisible; 

 and yet others exhibit intermediate sizes. 

 In file laboratory we have experimented 

 with feeding Creatonotos larvae different 

 amounts of pure PAs and have demon- 

 strated a direct correlation: the more PAs a 

 moth took up while it was a larva, the 

 larger its coremata and the more PA-de- 

 rived pheromone it produces. (No other 

 part of the moth is affected by these di- 

 etary changes.) 



Available phylogenetic evidence indi- 

 cates that adaptations to utilize pyrro- 

 lizidine alkaloids evolved several times in 

 various insect groups. Certain leaf beetles, 

 grasshoppers, and chloropid flies, for in- 

 stance, as well as numerous other species 

 of butterflies and moths, seek out these 

 chemicals independent of feeding. Experi- 

 ments have demonstrated that these in- 

 sects are attracted to the alkaloids, whether 

 they are presented in the form of dry plants 

 or laboratory dishes impregnated with the 

 chemicals. Not all these insects possess 

 male scent organs, so the chemicals' role 

 as a pheromone precursor is Hmited, and 

 not all insects that need them to produce 

 pheromones use them in the same way in 

 sexual communication. By improving 

 their chances of survival and perhaps by 

 increasing their reproductive success, 

 however, aU do better with PAs. For these 

 insects at least, purloining plant poisons 

 pays off. D 



32 Natural History 1/94 



