Observant home gardener Ria de Grassi recently noticed four buckeye caterpillars chomping away on her firecracker plant (Russelia equisetiformis). Not aware that this plant was considered a host plant for butterfly larvae, Ria snapped a few photos and sent them to UC Davis butterfly expert Dr. Arthur Shapiro for confirmation. Not only did he confirm her discovery of a new larval host plant for buckeye butterflies, he wrote a note about it for publication in the winter issue of the News of the Lepidopterists’ Society (see below).

It goes to show you that observant home gardeners are important citizen scientists – you never know what discoveries are waiting to present themselves. Now there’s yet another reason to love the firecracker plant; not only is it a low-water, long-blooming plant that hummingbirds love, it also appears to be larval host plant for buckeye butterflies!

by Dr. Art Shapiro, UC Davis professor of evolution and ecology

The Buckeye, Junonia coenia, uses the garden ornamental Russelia equisetiformis (Plantaginaceae) (“Firecracker Plant”) as a larval host in California

The common Buckeye, Junonia coenia (Nymphalidae), like many species of the very distantly-related Nymphalid genus Euphydryas, oviposits and feeds on a variety of plants that produce iridoid glycosides (Bowers and Puttick, 1986; Gardner and Sternitz, 1988; Bowers, 1984). The pattern of usage suggests that iridoids are necessary stimulants to oviposition and larval feeding but can be overridden by the presence of other chemicals that act as deterrents. It should not be surprising to find these butterflies using novel hosts that produce iridoids. Shapiro and Hertfelder (2009) reported the Variable Checkerspot, Euphydryas chalcedona, breeding spontaneously and repeatedly on Butterfly Bush (Buddleja) in the Sierra Nevada foothill county of Mariposa and the same phenomenon has now been reported in Mendocino County, in the North Coast Range (K. Hall, in litt.). In 2010 Shapiro and Biggs reported the Buckeye breeding spontaneously on the emergent aquatic plant Hippuris vulgaris (Hippuridaceae, an iridoid-producing member of the “Scroph clade”).  On 10 July 2017 one of us (RdG) discovered four Buckeye larvae feeding on the ornamental terrestrial shrub Russelia equisetiformis in her garden in Davis, Yolo County, in the California Central Valley. Russelia equisetiformis is named for a superficial vegetative resemblance to a Horsetail (Equisetum), but it is a flowering plant (cultivated for its abundant red, tubular, hummingbird-pollinated flowers) formerly placed in Scrophulariaceae and, in the wake of DNA-based reclassification of the “scroph clade,” now in Plantaginaceae. It in fact produces a variety of iridoid glycosides, one of them entirely novel (Ochi et al., 2012). We have been unable to find any previous records of the Buckeye on this plant, which is native to Mexico and Guatemala but very widely planted as an ornamental (occasionally as a container plant) in California and the Southwestern United States. It is occasionally cited in horticultural sources as vulnerable to damage by unidentified caterpillars.

LITERATURE CITED

BOWERS, M.D. 1984. Iridoid glycosides and host-plant specificity in larvae of the buckeye butterfly, Junonia coenia (Nymphalidae). J. Chem. Ecol. 10: 1567-1577.

BOWERS, M.D. & G.M. PUTTICK. 1986. Fate of ingested iridoid glycosides in Lepidopteran herbivores. J. Chem. Ecol. 12: 169-178.

GARDNER, D.R. & F>R> STERNITZ. 1988. Hostplant utilization and iridoid-glycoside sequestration by Euphydryas (Lepidoptera: Nymphalidae). J. Chem. Ecol. 14: 147-168.

OCHI,M., K. MATSUNAMI, H. OTSUKA & Y. TAKEDA. 2012. A new iridoid glycoside abd NO production inhibitory activity of compounds isolated from Russelia equisetiformis. J. Nat. Med. 66: 227-232.

SHAPIRO, A.M. & K. BIGGS. 2010. Use of Hippuris, an emergent aquatic plant, as a larval host by the buckeye, Junonia coenia, in Northern California.  J. Res. Lepid. 42: 79-83.

SHAPIRO, A.M. & K. HERTFELDER. 2009. Use of Buddleja as host plant by Euphydryas chalcedona in the Sierra Nevada foothills, California. News Lep. Soc. 51: 27, 39.

ARTHUR M. SHAPIRO, Center for Population Biology, University of California, Davis, CA 95616 amshapiro@ucdavis.edu

RIA DE GRASSI, de Grassi Consulting, Davis, CA 95616 <>

CAPTIONS FOR FIGURES

Fig.1. Larva of the Buckeye, Junonia coenia, on garden Russelia, Davis, CA.

Fig.2. Habit of Russelia equisetiformis in flower.