Investigating a Photolytic Metabolite in the Nocturnal Grasshopper Schistocerca ceratiola (Orthoptera: Acrididae)

The rosemary grasshopper, Schistocerca ceratiola Hubbell and Walker (Orthoptera: Acrididae), is unusual because it is one of only two known species of monophagous grasshoppers in North America and is nocturnal. S. ceratiola is a specialist herbivore of Florida rosemary, Ceratiola ericoides Michuax. Ceratiolin, the most abundant secondary metabolite in the plant, represents the only known example of a photoactivated allelopathic compound. Ceratiolin decomposes in sunlight to yield hydrocinnamic acid and other undescribed breakdown products. Due to the monophagous behavior, ceratiolin is ingested every time S. ceratiola feeds. Coupled with the nocturnal behavior of S. ceratiola, a connection to the photolytic properties of ceratiolin warrants investigation. We hypothesize that the breakdown products of ceratiolin represent potentially noxious compounds and S. ceratiola may exhibit nocturnal feeding behavior to avoid ingesting ceratiolin in sunlight where it readily decomposes. To our knowledge, this is the first chemical ecology study of a specialist herbivore of C. ericoides and a possible connection between the nocturnal behavior of S. ceratiola and ceratiolin. Qualitative analysis by liquid chromatography and tandem mass spectrometry was performed on the regurgitant, hemolymph, and frass of S. ceratiola to determine whether ceratiolin is confined to the gut or if it transports to the hemocoel. We also analyzed samples for the presence of hydrocinnamic acid to determine whether ceratiolin decomposes after it has been ingested. We detected ceratiolin in the regurgitant and frass. We did not detect hydrocinnamic acid in the regurgitant, hemolymph, or frass. Our results indicate that ceratiolin is confined to the grasshopper gut. We discuss more than one opportunity for future chemical ecology studies in this system.