Trail-following behavior and natural history of the social caterpillar of <i>Arsenura armida </i>in Costa Rica (Lepidoptera: Saturniidae: Arsenurinae).
Arsenura armida (Cramer) is a large, social Neotropical saturniid caterpillar that is common in the tropical dry forest of the Area de Conservación Guanacaste in northwestern Costa Rica. This aposematic caterpillar feeds side-by-side in highly visible nomadic groups in the crowns of at least three distantly-related tree species in early instars. In the last two instars, it rests in equally visible groups on the tree trunks in the day while ascending to the tree crown to feed at night. This species may to be unique among arsenurines in exhibiting these traits; all known caterpillars of other species in this subfamily are cryptic, and none is known to be social. Laboratory studies show that larval trail-following is elicited by surface cuticular material collected by wiping from the venter and dorsum of the abdomen of A. armida caterpillars. Crude extracts of somatic tissue also elicited trail-following. This is the first published demonstration of pheromone-based trail-following by a saturniid. The long-lived trail marker used by this species appears to be a component of the cuticle and is passively deposited from the posterio-ventral region of the abdomen as larvae travel over the host plant. Unlike other social Lepidoptera such as tent caterpillars, these trails are not deposited on silk, but rather directly on the plant substrate. A, armida larvae are capable of discriminating between extract-derived artificial trails differing in strength by a factor of 2 or greater. The trail marker is highly persistent on paper. In the laboratory, a 24-hour-old trail is nearly as attractive as a freshly deposited trail.
