Temporal change in the location of egg-laying by a bud-galling sawfly,Euura mucronata,on growing shoots of Salix cinerea

Summary Temporal change in the egg-laying behaviour of Euura mucronata was studied on growing shoots of Salix cinerea. Many new shoots arise from each previous year's shoot of S. cinerea; they grow very rapidly at the beginning of the oviposition period of E. mucronata, but their growth pattern changes dramatically during the 3 weeks of oviposition. When oviposition commences, all new shoots are equally long, and E. mucronata females lay eggs on them randomly; but toward the end of oviposition, eggs are laid on the longest of the new shoots, which originate on the distal part of the previous year's shoot. By the end of oviposition, the mean proportion of ovipositor borings that had resulted in egg-laying was 65.8% on distal shoots and declined linearly to 25% on shoots arising from the base of the previous year's shoot. The proportion of attacked buds from which larvae emerged declined non-linearly from 13.8% on the distal shoot to 3.5% on the basal shoots. The position of the shoot accounted for 67% and 73% of the variance in success of egg-laying and larval development, respectively.