Diets and trophic guilds of aquatic insects in Molino River, La Guajira, Colombia

Aquatic insects are considered a key component for stream food webs because of their contribution to the flow of energy from basal resources to the top predators. For this reason, the study of trophic guilds on aquatic insects is necessary to understand the transformation of energy and matter in stream ecosystems. The study of trophic guilds on aquatic insects has been widely documented in temperate streams. In contrast, little is known about feeding habits and trophic guilds in Neotropical streams. However, several lines of evidence indicate that aquatic insects in the Neotropical region are generally omnivores and that the Fine Particulate Organic Matter (FPOM) is the main food item. To test this hypothesis, we analyzed the diets and the trophic guilds of aquatic insects in an unexplored region of northern Colombia (Molino River, La Guajira). Aquatic insects were sampled using a Surber net, covering the different kind of substrates over a 100 m reach. Samples were sorted and identified to the lowest taxonomic level possible. We analyzed 250 guts of aquatic insects belonging to six orders, nine families, and 10 genera (Leptonema, Chimarra, Anacroneuria, Nectopsyche, Tabanus, Simulium, Pseudodisersus, Corydalus, Camelobaetidius, and Baetodes). We found that FPOM, algae, and animal tissue were the most important food items in the gut content of the aquatic insects at the Molino River. Our results suggest that aquatic insects in the Molino River are generally detritivores, highlighting the importance of the dead organic matter in Neotropical streams. We reported -for the first time- the trophic guilds of the genera Nectopsyche and Pseudodisersus, which were categorized as herbivorous. Our results suggest that aquatic insects in the Molino River exploit a variety of food resources and emphasize the importance of the study of feeding habits on aquatic insects in unexplored Neotropical streams.