Modular demography reveals subtleties of herbivore impact on plants, including, plant growth responses to herbivore damage, as shown by studies of the bud-galling midge. Rabdophaga sp. on its host plant, coyote willow (Salix exigua). Changes in bud populations for galled and ungalled shoots were followed over two seasons to detail Rabdophaga sp. impact on normal developmental processes of S. exigua. Galls were found to be highly condensed shoot segments when apical buds were galled, or condensed shoots when lateral buds were galled. In both instances, the gall was a dead-end in plant growth. Apical galls caused stunting of shoots and significant reduction in future growth and reproductive potential of galled shoots. Galled lateral buds were immediately lost from the bud population, but because lateral buds represent the beginnings of new bud lineages, bud losses were greater than just the loss of the attacked bud. For example, galled vegetative and reproductive buds. represented losses from the next generation of 19-23 buds and 7-8 buds, respectively. Salix exigua appeared to compensate for galling herbivory through the release of newly-formed lateral buds close to galls within shoots. However, the majority of lateral shoots produced in response to galling had abscised by the following growing season. Such information would have been lost had only the net outcome of herbivory been documented.
