Some factors in the distribution of European pine sawfly egg clusters in an experimental plantation of hard pines.

1. During three successive years the frequencies of oviposition by Neodiprion sertifer (Hymenoptera: Diprionidae) were observed in 546 pines (provenances of various hard pine species, hybrids between such species, and some white pines). The insects were able to discriminate between 30 host genotypes since in this preference test average oviposition frequency varied between genotypes. 2. Oviposition frequencies had to be inferred to from groups of feeding larvae. 3. Besides genotype, four other groups of variables had an effect on the number of larval colonies: position of a tre in the plantation (in terms of rows and columns), its dimensions, the dimensions of its neighbors, and the number o colonies in the neighbors. 4. Apparently different crown portions were preferred oviposition sites in the various genotypes. 5. Water potentials of a sample of host trees during the hatching period showed no relations to susceptibility.