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Journal of the Lepidopterists' Society 40(2), 1986, 130
OVIPOSITIONAL RESPONSE OF EUREMA NICIPPE (PIERIDAE) TO PHYLLANTHUS TENELLUS (EUPHORBIACEAE)
The host plants for Eurema spp. are mostly members of the legume subfamilies Mi-mosoidae and Caesalpinoidae. Most of the other members of the pierid subfamily Co-liadinae feed on other plants in the legume family (Fabaceae) (Howe 1975, The butterflies of North America, Doubleday, New York). All records associated with Eurema larvae in the collection at the University of Florida are for various species of Cassia (Caesalpinoidae) (Habeck, unpubl. data). Thus I was surprised to observe adult female Eurema nicippe (Cramer) alight in a dense patch of the exotic Euphorbiaceae Phyllanthus te-nellus Roxb. and display what appeared to be ovipositional behavior. During a three-hour period (0930-1230 h) on 7 October 1985 near Gainesville, Florida, I observed 46 instances of this behavior; I expected to find eggs on the Phyllanthus stems visited by the butterflies, and actually found 6 eggs. These were kept in petri dishes with fresh Phyllanthus; hatching larvae did not feed and wandered around the dishes. When offered leaves of Cassia chamaecrista L. (partridge-pea) three days later they immediately began feeding.
The leaves and growth form of Phyllanthus tenellus, a frequent weed of moist, shaded disturbed ground, strikingly resemble a usual host plant in northern Florida, Cassia chamaecrista (pers. observ. and Kimball 1965, The Lepidoptera of Florida, Division of Plant Industry, Florida). Cassia chamaecrista has pinately compound leaves, while the small leaves of Phyllanthus tenellus are closely arranged in a single plane along elongate side branchlets. This suggests that E. nicippe locates its host plant first by sight, but that because oviposition is infrequent on this incorrect host plant, secondary chemotactic responses are involved.
Another common host of Eurema spp. (including E. nicippe) in Florida is Aeschy-nomene americana L. (joint vetch), also a legume, but a distant relative of Cassia. Few of the other legume species are used by Eurema spp. The morphology of A. americana also strongly resembles that of Cassia chamaecrista. I propose that Aeschynomene has become a regular host plant of Eurema because of continued ovipositional mistakes on this common plant, and the taxonomic relatedness of Aeschynomene and Cassia. Could Phyllanthus eventually become a host plant for Eurema nicippe? If taxonomic relatedness is necessary for host switching to occur, probably not. But if biochemical similarity or an altered detoxifying system are possible, then host switching across wider taxonomic barriers might occur. If not, an improved host recognition in Eurema butterflies should evolve.
Within the genus Cassia there is a great variety of leaf morphologies. This diversity in leaf morphology could have evolved in response to the several genera and many species of Cassia-feeding pierids that rely on visual clues for host finding.
Michael J. Plagens, 4407 E. Lee, Tucson, Arizona 85712.
Date of Issue (Vol. 40, No. 2): 23 October 1986