Descrição
The study of three-trophic level interactions is crucial for the understanding of population dynamics of insect herbivores, especially for many gall-inducing species. We aimed to determine the developmental pattern of the nymphs of Baccharopelma dracunculifoliae and its relationship with gall size and natural enemies in Belo Horizonte, Brazil (19°30´S, 44°00´W). We sampled galls from the same cohort in two distinct surveys (June and August 1998). The galls were collected from 10 randomly selected individuals of Baccharis dracunculifolia in each survey. We then estimated their volume before dissecting them. Following, we counted the number of nymphs and the survivorship, also recording the mortality factors of the nymphs. The results indicate that the mean number of nymphs per B. dracunculifoliae gall did not differ between June and August, while the mean number of live nymphs was significantly higher in June than in August. Additionally, we found a weak correlation between the mean number of nymphs per gall and gall volume in both months of the study (r June = 0.11; r August = 0.17). We found higher nymph survivorship rates in June (95.0%) than in August (40.4%). Parasitism was responsible for the demise of 56.6% of all larvae in August and the rate of nymph survivorship did not vary with gall volume. Our findings suggest that during the development of B. dracunculifoliae the variation in gall size is more associated with nymph size than number of nymphs in a gall. The attack by natural enemies in B. dracunculifoliae is high, and parasitism is a strong force in the structure and regulation of the population, although it does not appear to be a selective force that acts on the oviposition behaviour of the female gallers since parasitism was not associated with gall and nymph size or with the clutch size.
