Trichoptera, or caddisflies, one of the largest groups of aquatic insects, are holometabolous insects with
aquatic larvae and pupae and terrestrial adults [1]. Trichoptera are potentially useful indicators of river and
stream health [2-4]. They are relatively easy to identify to species level in the adult stage and show a diverse
range of ecological, behavioral and functional feeding modes as larvae. Furthermore, they are good indicators
of environmental perturbation, and because they are distributed along the stream continuum, they constitute
one of the most interesting groups for studying the ecology of organisms in running water [5]
Previous studies on the use of adult caddisflies as a bioindicator of water quality in Thailand have been
reported by Chiabu [6], Laudee [7], Cheunbarn [8] and Prommi and Thamsenanupap [9]. Caddisflies were
chosen for this study because they are usually more diverse than other aquatic insect orders [10]. Adults have
been studied widely because they are easily collected by light traps and can be used as a useful tool for
bioassessment [11]. Chantaramongkol [2] recommends light trapping for assessing water quality in large
rivers. Knowledge of the taxonomy and ecology of the species has proven valuable in biomonitoring
programs because of differences in susceptibilities of the various species to pollutants and other types of
environmental disturbances. Genus or species level identifications of adult caddisflies are possible and clearly
produce more accurate results than family level identification, thereby giving better ability to assess the
change of water quality. The aim of this paper is to investigate the diversity and distribution of adult
Trichoptera from Mae Tao and Mae Ku watersheds. Water quality and some physicochemical factors were
also measured to determine their effects, if any, on the diversity and distribution of adult Trichoptera.