ADULT ACQUIRED RESOURCES AND CYANOGENESIS IN HELICONIUSBUTTERFLIES.

Márcio Zikán Cardoso
Dept. of Zoology, The University of Texas, Austin, TX 78712, USA.

Pollen feeding provides adult Heliconius butterflies with a steadysupply of amino acids that supports egg production and extended adult lives.I here report a new use for the pollen in Heliconius butterflies:as provider of precursors for synthesis of cyanogenic glycosides. Thesecyanoglucosides (linamarin and lotaustralin) are synthesised from the aminoacids valine and isoleucine and are considered the primary means of defenceof warning coloured Heliconius. Adults and larvae incorporate radiolabelledamino acids into cyanogenic glycosides via de novo synthesis, but evidencethat pollen derived amino acids had an effect on adult cyanogenesis hasnever been provided. Heliconius charitonia is a poor pollen collectorand is palatable, preumably becaused of low intake of amino acidsduring adult life. Freshly emerged individuals were randomly assigned totwo diet treatments: one consisting of amino acids normally present intheir pollen in a 20% sugar solution and a second consisting solely of20% sugar. Individuals from each diet treatment were kept in separate enclosuresin a greenhouse for 20 days. They were then assayed for cyanide concentrationthrough colourimetric analysis of individual butterflies. Amino acid fedadults showed significantly higher levels of these chemicals than individualskept on the sugar treatment. On the other hand, H. ethilla did notshow any difference between the two treatment groups. It seems that inthis species, larval obtained amino acids probably provide for their cyanogenesis,while adult obtained nitrogen is probably directed toward reproduction.This is the first experimental evidence tying adult acquired resourcesand palatability in the Heliconiinae.