The Composition and Distribution of Caddisflies (Trichoptera) Fauna in Khao Sok National Park, Surat Thani Province, Thailand

Khao Sok National Park is a protected area in Surat Thani Province, southern Thailand, in the western part of Surat Thani City. It consisted of the lowlands of the lower Phuket Mountain range, of the Indo-Malayan Mountain formations. Mountains are made of limestone and mostly covered with dense, moist tropical forest species. A survey was carried out along the Khlong Sok tributary of the Phum Duang River, which joins the Tapi River that empties into the Thai Gulf. The study was conducted from March-December 2019. Samples were collected (March-May) dry season and (July-December) wet season, summing up to three collections during the research. The results showed that a total of fifteen (15) families, thirty-eight (38) genera, and one hundred and eighteen (118) species were caught and identified. Families Philopotamidae, Ecnomidae, Hydropsychidae, and Leptoceridae were the most abundant and distributed groups, forming about sixty percent (60%) of the sampled caddisflies. Two new records were also found Cheumatopsyche opposita BANKS 1931* Cheumatopsyche contexta ULMER 1951*. Water quality parameters measured include temperature, dissolved oxygen, potential Hydrogen (pH), Electrical Conductivity and water Velocity. The study assessed the composition and distribution of Trichoptera fauna in Khao Sok National Park for management and conservationpurposes.

The world's tropical zone is considered the zone of the greatest diversity of flora and fauna because it contains most of the biologically diverse areas referred to as the hotspots of biodiversity [1]. The continent of Asia is located in this zone, consists of two biogeographical regions of Oriental and East Palearctic regions, and is regarded as the most extensive continent, characterized by diverse landforms and climatic conditions [2,3]. Loxdale [4] reported that insects are the most widely distributed terrestrial organisms on Earth, constituting about 75% of globally recorded fauna. Aquatic insects, a section of this group, spend part or the entire life in water; in most cases, the adult insects are found in terrestrial environments while the immature stages live in water. Studies showed that the largest populations of aquatic insects are found in Asia [5]. Three common aquatic insect orders, Trichoptera, Ephemeroptera, and Plecoptera, are commonly used in water quality condition assessments, especially in developed countries [6,7]. Accordingly, Valdon and Laudee [8], reported that aquatic insects inhabit vegetations close to water environments worldwide, where the juveniles make a substantial proportion of the benthic macroinvertebrates in freshwater habitats. Trichoptera fauna is one of the most varied and largely distributed in Southeast Asia, and their immature stages dominate macroinvertebrate communities in freshwater courses [9,10]. In Thailand, the diverse nature of caddisflies corresponds to the abundant assemblage of their larvae in freshwater environments [11]. Trichoptera larvae are important biological tools used to assess water quality conditions. They have been extensively exploited to measure water quality parameters because larvae of different families or species differ in their ability to respond to a wide range of water conditions [12]. Aquatic insect larvae and other macroinvertebrates are staple food for many freshwater fishes. Caddisfly larvae are an extensive group of macroinvertebrates that play vital roles in energy transfer, occupying different trophic levels of consumers, tertiary consumers even as predators [13]. The level to which an aquatic environment supports fish production can be measured by the corresponding abundance of certain aquatic insects’ larvae; therefore, efficient production and management of fish are attainable with high abundance [14].

This study aimed to assess the composition and distribution of Trichoptera species along the Khlong Sok tributary and observe the water quality parameters for conservation purpose.

Site selection was based on a combination of factors such as habitat types, ecological features and accessibility. Samples were collected by the use of a UV-Pan light trap. The equipment consists of a 15W fluorescent tube, placed on a plastic container of about five litres capacity, holding about two liters of water with few drops of detergent. The fluorescent is connected to a 12 X DC battery, and left overnight at each sample site. This was repeated at each site during every sample collection (Table 1). The UV-Pan light trap was expected to provide about six hours of light from 6:00 pm -12:00 midnight. Trichoptera insects are easily attracted to Ultraviolent light, therefore, as they perch on the tube many fell into the water containing detergent and died, hence they were collected in such manner. This process was replicated three times at each site, water quality parameters were also measured during each sample collection. Specimens obtained were preserved in 70% alcohol, labelled (stream name, date and time of sampling) and conveyed to Prince of Songkhla University, Surat Thani Campus laboratory, where they were analyzed. Trichoptera were first sorted from the sample, sorted specimens were separated into males and females, and after grouped according to families. The posterior part of the male abdomen was cut and removed in the process, soaked in 10% Potassium Hydroxide (KOH) solution, and heated for 30-60°C minutes. After heating, the structure would be observed under a microscope and compared with Malicky's [15] structures of Southeast Asian Trichoptera; the specimen would therefore be identified as a species. Identification was carried out under the supervision of Professor Pongsak Laudee of PSU Surat Thani and validated by Hans Malicky an expert of Southeast Asian Trichoptera based in Vienna, Austria (Tables 2-4).

The diversity of Trichoptera along the Khlong Sok stream showed that fifteen (15) families, thirty-eight (38) genera, and one hundred and eighteen (118) species were found in the area. The Family Leptoceridae had the highest number of thirty-two (32) species, followed by the Hydropsychidae family, which was represented by twenty-four (24) species. Family Philopotamidae had fourteen (14) species; Family Ecnomidae had thirteen (13) species; Family Polycentropodidae had six (6) species; Psychomyiidae had seven (7) species. Family Dipseudopsidae had five (5) species; Family Hydroptilidae had four (4) species; Families Goeridae and Lepidostomatidae had three (3) species each. Families Helicopsychidae and Calamoceratidae had two (2) species each, while Rhyacophilidae, Stenopsychidae, and Odontoceridae had one (1) species each. Setodes okyrrhoe in Family Leptoceridae had the greatest abundance of 657 individuals observed out of the total of 1,776. Cheumatopsyche charites in the Hydropsychidae family had more than 700 individuals out of 1.092, while Chimarra bimbltona in the Philopotamidae family had more than 90 individuals out of 365 observed. The highlighted species are the most abundant observed in their various families during the research. This showed that the site had a high diversity of species that were moderately distributed. Distribution signifies the nature of dispersion of each species, while abundance is the number of individuals in each of the species across the sites [16]. Therefore, it could be concluded that the extensive composition of insects with a corresponding large proportion of larvae observed in water agreed with the report of Holzenthal RW, et al. [12]. The pattern of distribution observed is similar to that reported by Prommi T, et al. [17] in streams of northern Thailand. Two new records of Cheumatopsyche opposita BANKS 1931* and C. contexta ULMER 1951* in the Family Hydropsychidae were observed by Valdon and Laudee [8]. Four thousand six hundred and twenty-seven (4,627) specimens were caught and observed during the survey. The high composition of caddisfly species observed is in line with reports of [11,3,5,18]. That there exists a high diversity of caddisflies in the Oriental region, especially Southeast Asia. In addition, this study supported the findings of Muray Stocker KM, et al. [19] that families Leptoceridae and Hydropsychidae are the most widely spread Caddisflies in the Oriental region. Water quality parameters observed had the following values: temperature ranges from 22.53-24.04°C, pH 7.41-8.44, dissolved oxygen 7.28-7.67 mg/l, electrical conductivity 42.69-80.95 µЅ/cm, and water velocity from 0.16-0.26 m/s. Most of the values obtained in this study contrasted those observed by Maneechan and Prommi of temperature. Dissolved oxygen, pH, electrical conductivity, etc., from the research conducted on Diversity and Distribution of Aquatic Insects in Streams of the Mae Klong Watershed, Western Thailand. The high level of dissolved oxygen recorded in this study indicated that the water condition of the habitat is good and is responsible for the large number of insects and larvae in the area. It could be concluded that there are minimal or no pollution effects in the water environment studied.

It was concluded that the area had a high diversity and distribution of Trichoptera fauna, associated with massive numbers of larvae in the stream. This indicated that the water condition in the stream was of good quality, with minimal or no risk of pollution contaminants. The result is important for record purposes and conservation management strategies in the future.

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