The galls occur more commonly on plants under stress, i.e. very dry conditions, waterlogging or hedge cutting, whereas vigorously growing plants are less commonly found to have galls. Whether the vigorous plant suppresses gall formation or is avoided by the wasp in favor of easier targets is unknown. Young and damaged plants tend to produce larger and more numerous galls than old and intact ones. In the latter, many eggs are laid, but the number of galls formed is relatively few.
