Distribution of aquatic insects in Ton Nga Chang wildlife sanctuary, Songkhla

This study of stream insects in 6 sites of Ton Nga Chang waterfall was conducted between October 11st and November 10th 1996 using surber sampler with an area 30 cm X 30 cm and with a mesh size 300 micron. Sites were classified as disturbed or undisturbed and each site included 4 habitats (detritus, cobbles, gravel, sand) for comparison. The aims of this study were to investigate insect composition, the ralationship between stream physical factors (water velocity, temperature, depth, width and dissolved oxygen) and the number of insect families, total number of insects and number of insects in each order, and to determine the effect of stream and type of habitat on the number of insect families, total number of insects and the number of insects in each order. The composition of aquatic insect, included 49 families and 9 orders. The aquatic insects which had the highest number of individual insects was order Ephemeroptera (413 individuals). Order Megaloptera had the lowest number of individual insects (2 individuals). None of the physical factors was found to have a significant effect on the number of insect families or total number of insects. When each order of insects was observed separately, order Hemiptera had a negative correlation with stream depth and a positive correlation with water temperature (P0.05), whereas order Diptera had only a negative correlation with water temperature (P0.05). The following relationships between type of stream and habitats were found: 1. Type of stream was found to have a significant effect on the number of insect families (P0.01, total number of insects (P0.05), and number of individuals of the orders, Ephemeroptera (P0.001), Odonata (P0.01) and Plecoptera (P0.01) 2. Type of habitat was found to have a significant effect on number of families (P0.001), and number of individuals of the orders Hemiptera (P0.001), Coleoptera (P0.05), Trichoptera (P0.001) and Megaloptera (P0.05). 3. The interaction between stream and habitat was found to have a significant effect on the number of insect families (P0.01), total number of insects (P0.05), and number of individuals of the order, Odonata (P0.05), Coleoptera (P0.001) and Lepidoptera (P0.05).