OVIPOSITION PREFERENCES IN PINE SAWFLIES - A TRADE-OFF BETWEEN LARVALGROWTH AND DEFENSE AGAINST NATURAL ENEMIES

The oviposition preferences and performance of a monophagous pine sawf ly (Neodiprion sertifer) were studied in the held on 61 naturally rege nerated Scots pine trees. The preference of sawfly females, measured a s the proportion of available shoots on a tree with egg batches, was f ound to be positively correlated with tree height and needle length in a multiple regression analysis. Females also seemed to prefer trees w ith high resin acid (diterpenoid) concentrations. Low variation among trees with respect to resin acid concentration, together with positive covariance between these concentrations and needle length, made it di fficult to evaluate the role of resin acids. Even though pupae weighed less and larvae suffered higher mortality when protected from natural enemies on trees preferred by females, there were benefits associated with oviposition on such trees, i.e. uncaged larvae were less vulnera ble to parasitoids on high resin acid trees. This indicates that femal es preferred trees on which their offspring gained enemy-free space ov er trees on which performance was high, which also was suggested by th e weak interaction found between the effect of caging (enemy exposure) and oviposition preference on survival in early instars.