Eucalyptus oils in the defensive oral discharge of Australian sawfly larvae (Hymenoptera: Pergidae).

Sawfly larvae of the subfamily Perginae have a diverticular pouch of the foregut in which they store an oily fluid that they regurgitate when attacked. The fluid, which is an effective deterrent to ants, birds, and mice, is essentially identical chromatographically to the oils of the Eucalyptus leaves on which the larvae feed. The significance of the defensive use by animals of the "secondary substances" of their food plants is discussed.