^^,^^**^-^ 



'V?**-- 



'^'^'Sss'iQB.r.^-. 



■^^ 



V 





'*;■■■■ 1 



why does she seem to use them in select- 

 ing a mate? 



As the research teams of Thomas Eisner 

 and Keith S. Brown, Jr., have demon- 

 strated, male milkweed butterflies transfer 

 more than just sperm to the female during 

 copulation: included in the ejaculate is a 

 mass of pyrrolizidine alkaloids, previously 

 collected by the adult male from plants. 

 This nuptial gift varies from male to male: 

 the more of the alkaloids a male has taken 

 in, the more his personal perfume will 

 smell of dihydropyrroUzines and the more 

 PAs he has to offer a female. Thus, if a 

 male's aroma is an indication of the size of 



the nuptial gift he is likely to present, the 

 female may have a meaningful basis for 

 choosing a mate: the more alkaloids she 

 can get from the male, the more she will 

 possess to protect herself and to incorpo- 

 rate into her eggs for their protection, too. 

 Studies of the chemical ecology of 

 milkweed butterflies led to a better under- 

 standing of other insects that utihze PA- 

 containing plants as grocery stores and 

 pharmacies at the same time. The larvae of 

 several tiger moth species (family Arcti- 

 idae) store PAs for their protection, and 

 some also use them as pheromone precur- 

 sors. Although many are speciahzed to 



feed on PA plants exclusively, not aU are 

 capable of detecting PAs directly. Among 

 the most interesting of the PA moths are 

 those such as Creatonotos species, which 

 respond to PAs behavioraUy, as danaines 

 do. The larvae of these moths can feed and 

 develop perfectly well on a variety of 

 shrubs, including some that contain PAs 

 and others tiiat do not. Under experimental 

 conditions, however, these caterpillars 

 show a definite interest in flie alkaloids, 

 feeding eagerly on almost any material, 

 mcluding fiberglass disks, as long as the 

 material has been first impregnated with 

 the chemicals. As with the milkweed but- 



31 



