Nelida E. GOMEZ*, Ludger WITTE, and Thomas HARTMANN
Institut für Pharmazeutische Biologie der Technischen Universität Braunschweig.
Mendelssohnstraße 1, D-38106 Braunschweig, Germany
Cassidinae larvae construct and carry an arched structure made of waste material (exuviae and feces) covering their dorsa. When larvae are tactically stimulated shields are held up, swatted heavily, and directed toward the site of stimulation. Larval shields have been shown to be effective against some predators in natural habitats. However, there is still speculation about the presence and origin of repellent or deterrent substances in cassidine larval fecal shields. We have examined the fecal shield of Eurypedus sp and its host plant Cordia curassavica, (Boraginaceae) from both field and green-house collections For this investigation a micro-method for extracting essential oil was established. Quantification was carried out by on-column gas chromatography.
Larval fecal shields of Eurypedus sp. contained essential oil derived from C. curassavica. Three out of seven plant monoterpenes (i.e. ß-terpinene, camphene, and ß-pinene) and of the many plant sesquiterpenes caryophyllene, appeared in fecal shields. Oxidised mono- and sesquiterpenes which were not found in the host plant were also detected in the shields. All samples from the wild yielded higher concentrations of essential oils than those from the green house. Young leaves from both sites contained higher amounts of these volatiles than older leaves (cassidine larvae normally feed on young leaves) On a dry weight basis larval fecal shields from both sites contained only half the amount of essential oil as compared to young leaves. Questions about the presence of these volatiles substances and their role in the defense of cassidine larvae and their time of residency in the shields are due to be answered.