Riqueza de espécies, abundância e sazonalidade de Hymenoptera em vegetação de caatinga e floresta ciliar, Semiárido Paraibano.

Abstract

Hymenoptera is one of the most diversified insect orders, with a variety of kinds of biologies and different sociality levels. The tropical semiarid region of Northeastern Brazil presents distinct kinds of vegetation, with a spatial heterogeneity, which can be grouped essentially in two kinds: dry and mesic areas. The present study aimed to study the species richness, abundance and seasonality of Hymenoptera fauna in two near areas, one of xerophilous vegetation (caatinga) and other near a riparian forest, at Paraiba state, specially to evaluate the possible role of mesic areas as a refuge for insects in this dry region. Two malaise traps were used to collect insects weekly in a continuous way for one year. 5697 individuals were collected belonging to twelve superfamilies, 35 families and 418 morphospecies. The family with a higher frequency of capture was Formicidae, followed by Crabronidae, Chalcididae, Vespidae, Pompilidae, Mutillidae, Bethylidae, Ichneumonidae, Bracronidae, and Apidae. These ten taxa grouped corresponded to 92,15% from all the individuals. The highest species richness was observed in Chalcididae, Crabronidae, Formicidae, Braconidae, and Pompilidae, respectively. These five taxa altogether corresponded to more then fifty percent of all species recorded. The area near riparian forest had a significantly (t-test, α<0,05) higher Shannon diversity index (H’=4.254) than caatinga (H’=3.892), what was due to the higher species richness (335 and 269, respectively), because evenness was similar. The estimated species richness by Chao 1 method in both areas indicated that 72% of species present in the areas were collected, and the riparian forest with the higher number of species. The weekly samples from riparian forest tended to have more species than those from caatinga, but this was not observed for the individuals and the number of families. The number of individuals and species were higher in the rainy season, from January to June (3612 and 365, respectively), as compared to that of the dry season (2086 and 213). The weekly samples from the dry season tended to have less individuals and species, both in the caatinga as in the riparian forest. The species richness was similar in the two areas in the rainy season, but a greater reduction was observed in caatinga area during the dry season. Specimens and species number variation had no significant correlation (Spearman) with rainfall, relative humidity or temperature. But when each family was analyzed separately some had correlation between the number of individuals and one or two climatical factor. The higher species richness and abundance of individuals in the riparian forest is interpreted as an evidence of its role as a refuge for the insect fauna, but there is a need for more detailed taxonomic analysis because each species may present different strategy to overcome the unfavorable season and to survive in this tropical dry region.