Eri silkworm larvae, Samia cynthia ricini (Boisd.) (Lepidoptera: Saturniidae), were fed with leaves of ten different provenances of physic nut (Jatropha curcas L., Euphorbiaceae) from Africa, Asia and the Americas. Only those from Veracruz (Mexico) and Santa Lucia (Nicaragua) enabled the insects to complete their life cycles. The most suitable provenance, Santa Lucia, showed lower pupation rates, adult emergence rates, cocoon, chrysalis and cocoon cortex weights, longer development times and lower fertility than moths reared on castor leaves (Ricinus communis L., Euphorbiaceae). A combination of Sta. Lucía leaves during the first four larval stages and castor for the fifth instars showed a significant improvement on Sta. Lucía regarding cocoon, chrysalis and cocoon cortex weight, larval and pupal development time as well as oviposition frequency and number of eggs. The same combination in reverse order did not improve performance compared with the diet consisting of only Sta. Lucía leaves. No correlation could be found between eri silkworm feeding on the leaves and phorbol ester content of the seeds, which indicates that different mechanisms are accountable for the lack of eri silkworm development and the toxicity of seeds to humans and livestock.