How do rattleboxes protect ornate moths?

By Chelsie Vandaveer

September 18, 2002

There are thirteen rattleboxes (Crotalaria species Linnaeus) in Florida; four are native and nine are introduced. The common name comes from the loose seeds in the dried pods. The exotic species are generally found in disturbed habitats (cattle pastures and old fields) where they pose a threat when forage is low. Crotalaria contain pyrrolizidine alkaloids, primarily monocrotaline and usaramine. The toxins cause liver, lung, and cardiovascular damage, but are so distasteful that grazing animals usually avoid the plants.

The ornate moth (Utetheisa ornatrix Linnaeus) is a native species which has adapted to at least two of the exotic rattleboxes, Crotalaria retusa and C. pallida. Brightly patterned in coral pink, white, and black, the ornate moth is diurnal (active during the day). The coloration keeps 'educated' predators away.

In a study at Archbold Biological Station, a team led by Thomas Eisner (Cornell University, 2000) found that the ornate moth caterpillars ingest the pyrrolizidine alkaloids (PA) as they feed on the rattleboxes. In the males, a portion of the alkaloids is converted into a pheromone, hydroxydanaidal, some is reserved for his protection, and remainder becomes part of the spermatophore (sperm packet). The ornate moth's spermatophore contains sperm, nutrients, and alkaloids.

The PAs ingested by the female caterpillars will be transferred to protect the eggs. When a female ornate moth is ready to mate, she is chemically defenseless since her PAs are now in the eggs. She releases a pheromone to attract the male ornate moths. The male moths then release their pheromones during the courtship flight. Unlike the male's pheromone, the female's is not derived from the alkaloids.

The male's pheromone apparently serves as a chemical clue to the amount of PAs (and protection), he will transfer to her. She picks the male and within minutes of mating, the alkaloids spread through the female's body. She has enough sperm to fertilize hundreds of eggs and additional nutrients to lay healthy eggs.

The Institut National de Recherche Agronomique has a great photograph of the ornate moth. To view the photograph, click on the link:

http://www.inra.fr/Internet/Produits/PAPILLON/arctiid/texteng/u_ornatr.htm

The Institute for Systematic Botany, University of South Florida has photographs of Crotalaria retusa and Crotalaria pallida taken by Betty Wargo and Bob Bierman. To view the photographs, click on the links:

http://www.plantatlas.usf.edu/images.asp?plantID=1669

http://www.plantatlas.usf.edu/images.asp?plantID=1425#

Click on the thumbnails to enlarge the images.