Introduction

Caddisflies are among the most successful and diverse organisms in freshwater habitats, with about 15,000 described species around the world, divided into 49 extant families and 616 genera (Holzenthal et al., 2007, 2015). As in other insect orders, Trichoptera taxonomy is mainly based on adult features, but they are better known for the building behavior of their larvae. Trichoptera and the megadiverse Lepidoptera—moths and butterflies—are sister groups and constitute the superorder Amphiesmenoptera, characterized by many morphologic apomorphies (Kristensen, 1997), including the larvae having a modified salivary gland opening on the labium that produces silk. Additionally, molecular data consistently corroborate the monophyly of the superorder (Kjer et al., 2006; Misof et al., 2014). In Lepidoptera caterpillars, the silk is used mainly to spin cocoons; in caddisfly larvae the silk is used to build portable cases, commonly composed of mineral grains or leaves and twigs, or retreats with silken nets for food capture. Trichoptera diversity and success, in some part, are the results of the various ways in which silk is used among the different groups, allowing larvae to exploit different kinds of available food resources and microhabitats (Mackay & Wiggins, 1979).

Immature stages of Trichoptera, from egg to pupa, are aquatic, and only the adults are terrestrial. Caddisfly larvae are especially abundant and diverse in running waters (lotic habitats), but they can be also found in standing water (lentic habitats), especially in temperate latitudes. At least one specie (Phylloicus bromeliarum Müller, 1880) is recorded living in water retained in bromeliad tanks. Trichoptera can occupy virtually every available substrate in rivers and streams, where they usually play a key role in energy flow (Resh & Rosenberg, 1984). In the Neotropics, some larvae are specialized to live in semiaquatic areas, such as rock surfaces above the water line, as seen in Xiphocentronidae and some Leptoceridae. Others are commonly found in madicolous habitats, with just a thin layer of water flowing over them, or in the spray zone of waterfalls, as in several Hydroptilidae genera.

After hatching and before pupating, caddisfly larvae complete five instars. The immature stages represent the longest part of the life cycle and are when they build their cases or retreats. In general, three groups can be defined according to larval construction behavior (Wiggins, 1996, 2004): fixed retreat-makers (Annulipalpia), portable case-makers, and closed cocoon-makers (Integripalpia). Retreat-making caddisflies usually build a fixed shelter of material from the substrate, also held together with silk, and from which they also spin a silken net to capture food particles from the water current (Wiggins, 2004). In some, the retreat itself is also the filter or capture structure. Philopotamids have a series of labial grooves associated with the silk gland opening that allow the larvae of this family to spin about 70 threads simultaneously, and they are used as a sac-like net with the smallest mesh opening known (0.5–5.5 microns), which enable them to feed on fine particulate organic matter, as well as associated bacteria and fungi (Wallace & Malas, 1976). Case-making caddisflies include those that typically build tubular, portable cases. Cases usually include material from the substrate, such as small fragments of leaves, sand grains, or small pebbles, twigs, or even empty mollusk shells. Silk acting as glue or mortar holds these components together. Although the portable case acts primarily as a camouflage or protective device against potential predators, it also has an important function in increasing respiratory efficiency (Wiggins, 1996). Thus, the case probably enabled caddisflies to exploit oxygen-poor habitats, such as some lentic waters (Wiggins, 2004; Malm et al., 2013). Closed cocoon-making caddisflies are a more heterogeneous group and include larvae that build a cocoon (closed to circulation of water) only for pupation (Wiggins, 2004). The cocoon-makers include larvae that build cases in all larval instars, only the last larval instar, and those that build no larval structures.

The Neotropical Region contains the second highest diversity of caddisflies species in the world, with a correspondent variety of types of retreats and portable cases. Only the Oriental Region has more species. Currently, about 3280 caddisfly species are known from the Neotropics (Holzenthal & Calor, 2017), but many new species continue to be described every year from the region. Forty-six new species were described for the Neotropical Region only in the first semester of 2017 (Barcelos-Silva et al., 2017; Cavalcante et al., 2017; Desidério et al., 2017; Dumas et al., 2017; Quinteiro & Holzenthal, 2017; Rocha et al., 2017; Souza & Santos, 2017 Valarino & Calor, 2017). In addition to providing descriptions of new caddisflies from the Neotropical Region, a more challenging task is to associate the immature stages and study their ecology and behavior. To date, 25 families and 155 genera have been recorded from the Neotropics; however, for 41 genera the immature stages remain completely unknown (Table 1), and knowledge of larvae and pupae at the species level is even less well known.