PREFERENCE AND PERFORMANCE LINKAGE IN A PHYLLOCOLPA SAWFLY ON THE WILLOW, SALIX MIYABEANA, ON HOKKAIDO

A leaf-folding sawfly in the genus Phyllocolpa (Hymenoptera: Tenthredi nidae) attacking Salix miyabeana (Salicaceae) was studied near Sapporo , Hokkaido, along the Ishikari River in 1993. Host plant individuals w ere young trees 4-7 years old which were growing rapidly, producing so me long shoots with large leaves. On a gradient of shoot length classe s from 0-5 cm long to over 80 cm long, shoots were much more abundant in the shorter shoot length classes. However, attacks by ovipositing f emales increased as shoot length increased from 0 attacks on the short est shoots to 5.17 attacks per shoot on the longest shoots. The freque ncy of attack per leaf increased from 0 to 0.13 over the same range of shoot lengths. This pattern of attack resulted in a high frequency of larval establishment in feeding sites, between 0.96 and 1.00, in all attacked shoot length categories. However, probability of survival to a late instar larva increased with shoot length and corresponded to th e attack pattern, indicating a preference-performance linkage between female ovipositional decisions and larval survival. The patterns found for this Phyllocolpa species are similar for galling sawflies in Nort h America and Europe, especially in the genus Euura, members of which make stem, bud and leaf midrib galls. Extending the pattern to a Phyll ocolpa species broadens identification of pattern and ultimately the g enerality of the emerging theory on populations of galling sawflies.