Some peculiar aspects of danaid/plant relationships
1978
Rothschild, Miriam | Marsh, Neville
The two South American subspecies Danaus plexippus megalippe and D. plexippus erippus were reared on Asclepias curassavica (Oxford strain). The former became more emetic (tested on the pigeon) than extracts of the food plant, while the latter was much less so. The cardiac glycosides stored by D. p. erippus were insufficient to exert a characteristic digitalis-like effect on the isolated rat's heart. In our greenhouse both adult butterflies sequester pyrrolizidine alkaloids (PAs) from the juices of Senecio and Heliotropium and it is suggested that, for danaids as a group, especially Euploea and Amauris, the PAs may constitute the principal predator deterrents. In addition, it was shown that these butterflies themselves secrete cardioactive substances which can be demonstrated in larva and pupa reared on artificial diet (lacking leaf powder) if tested on the isolated rat's heart. These substances are not emetic, but, since they are lacking in cryptic species of Lepidoptera, it is thought that they may function as part of the Danaids' defence mechanism.
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