This is probably due to air temperature in forested sections is lower compared with open areas
due to variation in shaded areas. Most Trichoptera are nocturnal flies and prefer lower air temperature
(Collier et al., 1997). In addition, higher number of Hydropsychidae (Trichoptera) adults is probably
associated with availability of algal biomass (Quinn et al., 1997). The larvae are often attached to rocks,
facing the water flow, and feed on particles caught in their nets (Triplehorn and Johnson 2005). Other
caddisfly larvae such as Philopotamidae and Leptoceridae fasten their cases to rocks, wood debris and
other small objects in the stream (Triplehorn and Johnson 2005). Generally, substrate diversity indirected
affects the distribution of aquatic insects as it offers a favourable place for oviposition in several groups
of aquatic insects. Badcock (1953) reported that some caddisfly females appeared to be selective in term
of particular substrates to lay their eggs. In the present study, a sufficient number of oviposition sites at
stream from Champathong Waterfall was observed, including plenty of protruding rocks as well as trees
scattered along the stream banks, which could explain the high abundance of caddisfly in the present
study.