Fire Effects on a Palicourea rigida (Rubiaceae) Gall Midge: A Test of the Plant Vigor Hypothesis

Abstract

The effects of fire on growth of Palicourea rigida (Rubiaceae) were significant in a comparison between adjacent burned and unburned sites in cerrado savanna vegetation near Brasilia, Brazil. Many more small and young leaves appeared after the fire in the early part of the wet season, and leaves after the burn were much less tough for a given leaf length class than in the unburned area (unburned area leaves were 150% tougher). Growth of host plants after fire resulted in higher colonization of a leaf-galling midge in the genus Contarinia (Diptera: Cecidomyiidae) as yet unnamed at the species level. On the highest intensity of attack per leaf length class, galls were over five times more abundant per leaf in the burn than in the unburned area. Within the galls larvae survived better in the burned site, and numbers of surviving larvae at the end of the first generation were 5.4 times higher per leaf than in the unburned area. An even stronger effect of fire was observed in the second generation of gallers after the fire, when no living larvae could be found in the unburned area, but 17 living larvae per 100 leaves occurred in the burned site. These results supported the Plant Vigor Hypothesis, because regrowth after fire produced younger more tender leaves favorable for herbivore attack. The importance of fire in a landscape as a disturbance factor in cerrado, which rejuvenates plant growth, increasing favorability for many insect herbivores, deserves more attention and study.