Factors affecting components of fitness in a gall-making wasp (Cynips divisa Hartig).

The galls of the agamic generation of the cynipid gall-wasp Cynips divisa were studied; these galls are found only on the main veins of the leaf. Galls are concentrated on the middle veins of leaves, and generally occur closer to the midrib than to the edge of the leaf. Survival of the gall-maker and fecundity of the energing wasp depend on wasp size and position of the gall. There is a striking pattern in gall size according to the number of galls on the vein. The number of galls on a vein appears therefore to have a strong effect on potential fecundity.