Diversity of galling arthropods and host plants in a subtropical forest of Porto Alegre, southern Brazil.

Many hypotheses have been proposed to explain diversity patterns of galling insects. However, there are contradictory evidences on the evolutionary and ecological factors responsible for the trends. Furthermore, questions such as arthropod seasonality, sampling sufficiency and sampling team experience have been almost ignored. This study records galling arthropod diversity while paying attention to these questions. Seasonal sampling of galling arthropods and host plants were conducted in a humid subtropical forest of southern Brazil. Four transects were sampled twice per season, with two persons searching the vegetation for galls during 1h30min. After 96h.persons of sampling, 130 gall morphotypes on 84 species of host plants were recorded. An analysis of the numbers of galls and gall morphotypes found per transect along time showed that sampling team experience influences galler richness results and the interpretation of galler seasonality patterns. Different species had distinct seasonal patterns. Galling arthropod richness was bound to plant richness. Our results suggest that sampling team experience is an important factor that must be explicitly considered, as well as seasonality patterns of different galling species, at least for tropical/subtropical areas. Although sampling sufficiency was not reached, fauna heterogeneity at small spatial scales seems substantial: despite the proximity of the sampled transects (500 m), they harboured significantly specific faunas. This work adds to the literature records suggesting that both plant richness and specific composition of the vegetation have a strong influence on galler richness at least for local scales.