TEMPORAL AND INTER-TREE VARIATIONS OF ATTACK BY HYPSIPYLA-ROBUSTA MOORE (LEPIDOPTERA, PYRALIDAE) IN AUSTRALIAN RED CEDAR (TOONA-AUSTRALIS (F-MUELL) HARMES)

Temporal and inter-tree variations of attack of Hypsipyla robusta Moor e (Lepidoptera: Pyralidae) were studied with 13 sets of consecutive sa mpling data in a Red Cedar (Toona australis (F. Muell.) Harmes) planta tion over a 31 month period. The temporal pattern of infestation level s was closely correlated to rainfall: the larger the amount of rainfal l, the higher the infestation levels. Temperature did not appear to af fect the general infestation levels, but low daily minimum temperature s in the winter (less than 6.5 degrees C) were always associated with low proportions of attacked trees. Analyses of logistic regressions sh owed that the likelihood of attack of Red Cedar trees was affected pos itively by tree height, diameter at breast height (DBH), and the numbe r of shoots with fully expanded leaves, and negatively by tree form (t ree 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 intensit ies of attack are, however, negatively correlated with tree size. Mech anisms for the attack patterns are discussed. (C) 1997 Elsevier Scienc e B.V.