Effects of variation in Eucalyptus essential oil yield on insect growth and grazing damage.

Levels of insect attack and yields of leaf essential oils in Eucalyptus vary widely within and among species. We tested the hypotheses that 1) metabolic cost of oil detoxification increases with increasing oil yield, resulting in lower herbivore growth rates and, consequently, 2) in lower herbivore damage to plants. Distribution of insect damage, eggs, immature insects and adults and feeding rates, growth and survivorship of insects do not support the hypotheses, although a threshold level of oil may be necessary to influence herbivorous insects. Herbivorous beetles tested do not detoxify essential oils. Levels of leaf nitrogen, rather than oil content, explained differences in insect feeding and growth.