Sampling methods for assessing syrphid biodiversity (Diptera: Syrphidae) in tropical forests

When assessing the species richness of a taxonomic group in a specific area, the choice of sampling method is critical. In this study, the effectiveness of three methods for sampling syrphids (Diptera: Syrphidae) in tropical forests is compared: Malaise trapping, collecting adults with an entomological net, and collecting and rearing immatures. Surveys were made from 2008 to 2011 in six tropical forest sites in Costa Rica. The results revealed significant differences in the composition and richness of syrphid faunas obtained by each method. Collecting immatures was the most successful method based on numbers of species and individuals, whereas Malaise trapping was the least effective. This pattern of sampling effectiveness was independent of syrphid trophic or functional group and annual season. An advantage of collecting immatures over collecting adults is the quality and quantity of associated biological data obtained by the former method. However, complementarity between results of collecting adults and collecting immatures, showed that a combined sampling regime obtained the most complete inventory. Differences between these results and similar studies in more open Mediterranean habitats, suggest that for effective inventory, it is important to consider the effects of environmental characteristics on the catchability of syrphids as much as the costs and benefits of different sampling techniques.