WITHIN-TREE DISTRIBUTION OF ATTACK BY HYPSIPYLA ROBUSTA MOORE (LEPIDOPTERA, PYRALIDAE) IN AUSTRALIAN RED CEDAR (TOONA-AUSTRALIS (F-MUELL) HARMES)

Field and laboratory evaluations were made of the within-tree distribu tion of attack of Hypsipyla robusta in Australian Red Cedar (Toona aus tralis). Proportions of shoots attacked by the insect increased with s hoot height, relative shoot height, shoot length, shoot basal diameter and shoot slenderness (shoot length/shoot basal diameter). The most s ignificant factor influencing the log-odds of attack of shoots was the ir relative height. Shoots positioned at above 90% of tree height were attacked twice as often as the lower-positioned shoots. This suggests that terminal shoots would be among the first to be attacked once a t ree is attacked. There was a gradual shift of feeding loci with respec t to host tissues as the larva aged. Feeding by larvae of the first tw o instars was found most often in terminal foliage or previously damag ed tissues of shoots or tree stems. Pith-feeding (tunnelling) started at the later 2nd instar. On average, a larva initiated feeding in a me an of 5.4 different locations during its life time, with a minimum of three and a maximum of II. Switching of feeding loci was most frequent during early 1st instar and much of the 3rd and early 4th instars. (C ) 1997 Elsevier Science B.V.