Abstract
The factors that affect oviposition and consequently spatial distribution of the galls of many gall makers are poorly understood. Knowledge of these factors could result in a better understanding of the mechanisms that initiate and regulate the development of galls. We tested the hypotheses that, regardless of tree height, galls of Cynips quercusfolii L. produced agamically are distributed randomly in the crowns and on the veins of leaves of oak trees. This study was done in Poland on 15 pedunculate oak (Quercus robur) trees of various heights. We measured the areas of 1659 leaves, including 192 leaves with galls, and the distances along a vein from a gall to the petiole and from gall to leaf edge. The number of galls did not depend on tree height but depended on the position of the leaf within the crown (upper or lower). Regardless of the position in the crown, leaves with galls were significantly larger than those without galls. We conclude that galls were located at a fixed distance from the edge of leaves irrespective of leaf size, but the distance from the gall to the leaf petiole depended significantly on leaf size. We conclude that agamic females of C. quercusfolii prefer large leaves and choose the site on a leaf on which to deposit their eggs. This probably ensures that the developing gall obtains the required amount of nutrients and assimilates.
Highlights
Trees of the genus Quercus (Fagaceae) host numerous insect species that form galls, the biology of gall-forming insects and their interactions with host plants are still poorly understood
We analyzed all of the leaves on several oaks in order to determine the spatial distribution of the galls of the agamic generation of the oak gall wasp Cynips quercusfolii L. (Hymenoptera: Cynipidae)
We tested the hypotheses that: (1) galls produced by the agamic generation of C. quercusfolii are evenly distributed in the upper and lower parts of the crowns of oak independently of tree height, (2) occurrence of galls is not related to the size of the leaves and (3) the distribution of galls on surfaces of leaves is random
Summary
Trees of the genus Quercus (Fagaceae) host numerous insect species that form galls, the biology of gall-forming insects and their interactions with host plants are still poorly understood. We analyzed all of the leaves on several oaks in order to determine the spatial distribution of the galls of the agamic generation of the oak gall wasp Cynips quercusfolii L. Second generation females and males emerge from these galls in early summer (June) Soon after their emergence, the females insert fertilized eggs into the veins on the underside of oak leaves, which develop in summer into large spherical galls with a single chamber. We tested the hypotheses that: (1) galls produced by the agamic generation of C. quercusfolii are evenly distributed in the upper and lower parts of the crowns of oak independently of tree height, (2) occurrence of galls is not related to the size of the leaves and (3) the distribution of galls on surfaces of leaves is random
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