Larval Behavior and Cannibalism in Heliothis zea (Lepidoptera: Noctuidae)

Abstract

Behaviors associated with intraspecific encounters in Heliothis zea (Boddie) larvae are described, and paired contests in laboratory arenas are used to determine the effects of sex, instar, and molting on cannibalism. The frequency of eight behavioral responses (freezing, flicking, striking, recoiling, wriggling, moving away, rolling, and no response) differed significantly among intermolting larvae of the five instars. Among all instars, the most frequent (>35%) response to contact was a recoil. When contacted by their opponents, later instars struck more often than did earlier instars, whereas first and second instars moved away or ceased movement more often than did later instars. Molting larvae struck at their opponents significantly less often than did intermolting larvae, and generally displayed less maneuverability. Sex of the larvae had no significant effect on cannibalism. Among intermolting larvae, later instars were highly successful against earlier instars; no larva cannibalized a later instar. The greatest amount of time (up to 96 h between fifth instars) was required for a larva to cannibalize another of the same instar. Molting larvae were especially vulnerable to cannibalism, particularly when paired with an intermolting larva of a later instar. In extended contests, intermolting larvae occasionally cannibalized molting larvae of later instars. The results of this study suggest that cannibalism in H. zea can be predicted on the basis of instar and molting status.