WILLOW TREE SHOOT MODULE LENGTH AND THE ATTACK AND SURVIVAL PATTERN OF A SHOOT-GALLING SAWFLY, EUURA-ATRA (HYMENOPTERA, TENTHREDINIDAE)

A small population of the shoot-galling sawfly, Euura atra (Jurine), a ttacking the willow, Salix alba L. (Salicaceae) in Joensuu, Finland, s howed strong preference-performance Linkage between female oviposition al choices and survival of progeny. Although shoot lengths on trees we re most common in the classes 200-400 mm, the probability of attack in creased with shoot length until rare long shoots over 400 mm had a 50- 80% probability of attack. The regression of attack probability on sho ot length class accounted for 91% of the variance in attack. Attack wa s significantly greater on longer shoot length classes than that predi cted by random attack based on total shoot length available per class, or total number of shoots per class. As shoot length increased the me an number of galls per shoot increased from 0 to 3 per shoot, and esta blishment and survival of progeny increased from 0 to over 60%. Shoot length class accounted for 70% and 50% of the variance in larval estab lishment and ultimate survival respectively, while attack by carnivore s showed no pattern and had no explanatory power. The results are cons istent with those from studies on seven other Euura species showing at tack on rapidly growing plants, an ovipositional preference for longer shoots, higher survival on longer shoots, and no detectable effects o f carnivores on pattern generation. The study aids in the development of a strong comparative ecology of galling sawflies and the eventual d evelopment of empirically based factual theory on their population dyn amics.