Sabotaging Behavior and Decision-Making in Larvae of the Queen Butterfly Danaus gilippus

Abstract

Sabotaging behavior and decision-making during ontogeny in herbivorous insects remain largely underappreciated. Insects that use hosts bearing articulated laticifers would be expected to cut trenches to deactivate this plant defense. Contrary to this expectation, larvae of Danaus erippus display vein cutting when feeding on Asclepias curassavica, a host with articulated anastomosing laticifers; the frequency of sabotaging varies according to ontogeny. Scant records indicate that larvae of the congener Danaus gilippus perform both trenching and vein-cutting on milkweeds. In view of this incongruency, we examined the sabotaging behavior of D. gilippus on A. curassavica during larval ontogeny. Continuous observations of D. gilippus on A. curassavica revealed that the larvae always sabotaged leaves before feeding. Leaves were selected by larvae of D. gilippus for size but not age. Early instars cut trenches on large leaves, and the frequency of trenching decreased as the larvae grew. Vein cutting became predominant in late instars, and petiole cutting was observed in all last instars. Because sabotaging behavior was ubiquitous, artificial trenches and cuts were made on intact leaves to examine if leaf severance affects sabotaging frequency; sabotaging decreased significantly in artificially damaged leaves. Although sabotaging behavior has a strong innate component in D. gilippus, information regarding leaf dimension and severance is important in the decision-making processes for sabotaging to take place. As D. gilippus differs from D. erippus with respect to sabotaging type and frequency when feeding on the same host, other factors than plant anatomy probably play a role in mediating sabotaging behavior in this butterfly group.