Intraspecific variation in food plant favourability to phytophagous insects: psyllids on Eucalyptus blakelyi M.

A combination of variables reflecting leaf quality provided the best predictive model explaining differences in population trend of Glycaspis spp. among individuals of the food plant Eucalyptus blakelyi , measured under field conditions on an egg to egg basis. The equation incorporated the product of: (1) proportion of foliage in each age class; (2) probability of foliage escape from herbivory; (3) preference for the foliage class measured as the proportion of eggs oviposited on it by the female; these variables being summed over the young and mature age classes. In addition, significant and consistent differences in insect survivorship among trees were demonstrated by transfer experiments. These experiments established that young foliage was preferable to mature foliage for first instar survival. Differences in insect survivorship also showed a consistent pattern among the study trees. The most probable explanation for this consistent pattern was the influence of the trees on the insects, particularly physiological or biochemical differences among trees. It was not, however, possible to identify the cause of the differences.