FIRE EFFECTS ON A PALICOUREA-RIGIDA (RUBIACEAE) GALL MIDGE - A TEST OF THE PLANT VIGOR HYPOTHESIS

The effects of fire on growth of Palicourea rigida (Rubiaceae) were si gnificant in a comparison between adjacent burned and unburned sites i n cerrado savanna vegetation near Brasilia, Brazil. Many more small an d young leaves appeared after the fire in the early part of the wet se ason, and leaves after che burn were much less tough for a given leaf length class than in che unburned area (unburned area leaves were 150% cougher). Growth of host plants after fire resulted in higher coloniz ation of a leaf-galling midge in the genus Contarinia (Diptera: Cecido myiidae) as yet unnamed at the species level. On the highest intensity of attack per leaf length class, galls were over five times more abun dant per leaf in the burn than in the unburned area. Within the galls larvae survived better in the burned site, and numbers of surviving la rvae 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 observ ed 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 1 00 leaves occurred in the burned site. These results supported che Pla nt 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 p lant growth, increasing favorability for many insect herbivores, deser ves more attention and study.