Oxidizable Phenolic Concentrations Do Not Affect Development and Survival of Paropsis Atomaria Larvae Eating Eucalyptus Foliage

Abstract

Insect folivores can cause extensive damage to plants. However, different plant species, and even individuals within species, can differ in their susceptibility to insect attack. Polyphenols that readily oxidize have recently gained attention as potential defenses against insect folivores. We tested the hypothesis that variation in oxidizable phenolic concentrations in Eucalyptus foliage influences feeding and survival of Paropsis atomaria (Eucalyptus leaf beetle) larvae. First we demonstrated that oxidizable phenolic concentrations vary both within and between Eucalyptus species, ranging from 0 to 61mg.g-1 DM (0 to 81% of total phenolics), in 175 samples representing 13 Eucalyptus species. Foliage from six individuals from each of ten species of Eucalyptus were then offered to batches of newly hatched P. atomaria larvae, and feeding, instar progression and mortality of the first and second instar larvae were recorded. Although feeding and survival parameters differed dramatically between individual plants, they were not influenced by the oxidizable phenolic concentration of leaves, suggesting that P. atomaria larvae may have effective mechanisms to deal with oxidizable phenolics. Larvae feeding on plants with higher nitrogen (N) concentrations had higher survival rates and reached third instar earlier, but N concentrations did not explain most of the variation in feeding and survival. The cause of variation in eucalypt herbivory by P. atomaria larvae is therefore still unknown, although oxidizable phenolics could potentially defend eucalypt foliage against other insect herbivores.