Summary. Larvae of
Trichoplusia ni Hübner (Lepidoptera: Noctuidae) that ingested latex from
Asclepias curassavica L. (Asclepiadaceae) often regurgitated and convulsed with spasms before becoming immobile and unresponsive. Some larvae required
over a day to recover sufficiently to feed. Latices from four other plant species in three families were all deterrent, but
none caused detectable poisoning. The toxicity of
A. curassavica latex was evidently due to cardenolides because pure cardenolides had similar effects when ingested by
T. ni. Other species of noctuid caterpillars (
Rachiplusia ou Guenée,
Anagrapha falcifera Kirby, and
Autographa precationis Guenée) sometimes also suffered spasms and temporary immobility when fed
A. curassavica latex. A more distantly related noctuid,
Spodoptera ornithogalli, was deterred by the latex, but showed no overt physiological responses at the dosage tested.
T. ni larvae failed to develop on intact leaves of
A. curassavica, on leaves with latex canals deactivated by midrib severance, and on excised leaves. Similarly, larvae reared on excised
A. syriaca L. leaves to the final instar died when transferred to
A. curassavica leaves with either intact or severed midribs. The final instar larvae sometimes suffered from spasms and immobility even
when confined on leaves with depressurized canal systems. Evidently, cardenolides stored outside the latex system suffice
to poison larvae. We conclude that cardenolides in
A. curassavica have potent physiological effects on some generalist caterpillars and that the presence of these compounds both inside and
outside laticifers effectively protects the plant.
Received 30 June 1999; accepted 18 October 1999
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