Irrigation and fertilization of Chrysothamnus nauseosus (Asteraceae) affect the attack and gall growth of Rhopalomyia chrysothamni (Cecidomyiidae)

Abstract

The quality of the environment and the host plant influence the development of the galls as well as the performance of gall inducing insects. The effect of nutrients and water availability on the development of galls induced by Rhopalomyia chrysothamni (Diptera: Cecidomyiidae) on Chrysothamnus nauseosus subsp. hololeucus (Asteraceae) was tested. The study was conducted in a xeric area with no signs of disturbances in Coconino National Forest, Arizona, USA. Individuals of C. nauseosus randomly selected underwent three treatments of water and nutrients availability. At the end of the growing season, the number of attacked plants, abundance and the development of galls in each treatment were evaluated. The differences in habitat quality simulated by the fertility and humidity conditions influenced both the number of attacked plants and the growth of galls. Plants with lower hydric-nutritional quality were more attacked by the galling insect. Otherwise, when both water and nutritional stresses were relieved plants developed galls with higher dry biomass and density. Therefore, this field experimental study indicates that while galling females attacked plants more in xeric environments, the galls grew larger in relatively more mesic conditions. The results showed a trade-off between the quantity and quality of galls of R. chrysothamni depending on the nutritional quality of the host plants.