The lethal plant defense paradox remains: inducible host-plant aristolochic acids and the growth and defense of the pipevine swallowtail

Toxic plants with sequestering specialists are presented with a problem bec ause plant derived toxins protect herbivores against natural enemies. It ha s been suggested that early induction of toxins and later relaxation of the se defenses may help the plant resolve this problem because neonate caterpi llars incur the physiological cost of dealing with toxins in early life, bu t are denied toxins when they are able to sequester them efficiently. In Ca lifornia. the pipevine swallowtail. Battus philenor L. (Lepidoptera: Papili onidae), feed exclusively on Aristolochia californica Torrey (Aristolochiac eae), an endemic vine that contains toxic alkaloids called aristolochic aci ds that caterpillars sequester to provide chemical defense in immature and adult stages. In a field experiment, the concentration of aristolochic acid s doubled in the plant following leaf damage and returned to constitutive l evels after six days. Neonate pipevine swallowtail caterpillars showed no a version to high levels of aristolochic acid in a preference test. Caterpill ars reared on leaves with supplemented aristolochic acid showed no physiolo gical cost or increased mortality compared to caterpillars reared on un-sup plemented leaves. Searching efficiency and capture rate of lacewing larvae (Chrysoperla), a common predator of first instar caterpillars, was compromi sed significantly after feeding on caterpillars reared on leaves with suppl emented concentrations of aristolochic acid compared to caterpillars feedin g on control plants. Additionally, mortality of lacewings increased when th ey were provided with a diet of B. philenor caterpillars reared on suppleme nted leaves compared to caterpillars reared on control leaves. Thus. the in duction of aristolochic acids in the plant following leaf damage does not r esolve the problem confronted by the plant and may confer benefits to this sequestering specialist.