Temporal and inter-tree variations of attack by Hypsipyla robusta moore (Lepidoptera: Pyralidae) in Australian Red Cedar ( Toona australis (F. Muell.) Harmes)

Abstract

Temporal and inter-tree variations of attack of Hypsipyla robusta Moore (Lepidoptera: Pyralidae) were studied with 13 sets of consecutive sampling data in a Red Cedar ( Toona australis (F. Muell.) Harmes) plantation over a 31 month period. The temporal pattern of infestation levels was closely correlated to rainfall: the larger the amount of rainfall, the higher the infestation levels. Temperature did not appear to affect the general infestation levels, but low daily minimum temperatures in the winter (less than 6.5°C) were always associated with low proportions of attacked trees. Analyses of logistic regressions showed that the likelihood of attack of Red Cedar trees was affected positively by tree height, diameter at breast height (DBH), and the number of shoots with fully expanded leaves, and negatively by tree form (tree height relative to DBH). The effects were probably due to the low attack frequencies of small trees (height less than or equal to 150 cm). For larger trees, the attack frequencies were similar. The intensities of attack are, however, negatively correlated with tree size. Mechanisms for the attack patterns are discussed.