Aquatic insects in streams in southern provinces of Thailand
1996
Watanasit, S. (Prince of Songkla Univ., Songkhla (Thailand). Faculty of Science. Dept. of Biology)
Aim of this study was to investigate aquatic insect composition and determine the relationship between physical factors and number of insect families and total number of insects in each order. This study of aquatic insects in 23 streams of 13 southern provinces of Thailand was carried out between March and April 1995 using hand net. Standard time for collection was 20 minutes. Nine orders of insects, including 53 families, were found, The stream which had the highest number of individaul aquatic insects (636 individuals) was Sutha Lai stream in Yala Province. The Ton Sai stream in Phuket had the lowest number of individual insects (11 individuals). The relationships between a stream's physical factors, such as water velocity, temperature, mean depth, width, dissolved oxygen and amount of bottom substrates available, and the number of insect families and total number of insects were explored. Velocity was positively correlated with the number of families and with the total number of insects in each order (P=.001, and P=.002, respectively). Temperature was negatively correlated with the total number of insects (P=.01). When each order of insects was observed separately, insect numbers of the orders Ephemeroptera, Plecoptera, Trichoptera and Diptera had a positive correlation with velocity (P0.05). The number of Trichoptera had a negative correlation with temperature (P0.05). One the other hand, none of the physical factors was found to have a significant effect of insect numbers of orders Odonata, Hemiptera, Coleoptera, Lepidoptera and Collembola (P0.05).
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