Plant age and attack by the bud galler, Euura mucronata.

As ramets of the willow, Salix cinerea L. (Salicaceae) aged shoot length decreased in the six populations studied in S.E. Finland. Many traits correlated positively with shoot length: basal diameter, number of internodes, internode length, leaf size, and length of growing period. The bud-galling sawfly, Euura mucronata (Hartig) Man. (Churchill) (Hymenoptera: Tenthredinidae), responded positively to shoot length or correlated traits, and negatively to ramet age in three forest populations. This herbivore attacked the most vigorous plants in a population, and numbers of attacks declined as ramets aged and senesced. The generality of this kind of herbivore response to plant quality is emphasized.