Abundance of Neopelma baccharidis (Homoptera: Psyllidae) Galls on the Dioecious Shrub Baccharis dracunculifolia (Asteraceae)

Abstract

We assessed whether temporal variation in gall abundance of Neopelma baccharidis Buckhardt on Baccharis dracunculifolia De Candole is determined by climatic conditions, availability of adults for plant colonization, tannin concentration in plant tissue, or attack by natural enemies. We verified the influence of host plant sex on the above-mentioned factors. Gall abundance varied during the study period and was higher on the reproductive phases (10.53 ± 0.87 galls per plant) than on the nonreproductive phases (0.89 ± 0.13 galls per plant) of the host plant. Gall abundance was not influenced by weather conditions. The abundance of adults in the field was not responsible for the pattern on gall frequency. No relationship was found between the frequency of gall dehiscence and abundance of adults. Mortality caused by natural enemies influenced gall survivorship but did not affect gall abundance in the field. Tannin concentration was higher during the reproductive phase (0.117 ± 0.017 mg/g) than the nonreproductive phase (0.042 ± 0.004 mg/g). Nevertheless, no relationship was found between tannin concentration and gall abundance, probably because of the feeding habit of galling insects. We found that the gender of the host plant did not influence gall abundance, tannin concentration, and gall mortality rates. These results suggest that the abundance of galls of N. baccharidis is probably determined by a plant trait that varies between phenological phases, such as other secondary compounds or mechanical defenses not evaluated in this study.