COMPOSITION AND ABUNDANCE OF ODONATES AT ALATORI STREAM SOUTH-WEST, NIGERIA

Abstract

Dragonflies and damselflies (Odonata) are sensitive to human disturbance both as adults that are on wings and as larvae that are aquatic. This attribute suggests their usage as assessment tool for determination of human disturbance within the ecosystem. Alatori stream in Akure Forest Reserve was studied from May 2008 to April 2010 in order to determine the water quality and abundance of Odonata species of the stream.  Adults and larvae specimens were sampled throughout the sampling period. A total of 767 adult specimens and 108 larvae were collected. Only 45.4% of the penultimate and ultimate larvae collected eclosed (emerged) to teneral adults. The composition of Odonata families occurring at the stream showed that Libellulidae was the highest (281) followed by Chlorocyphidae (158) while the lowest was Megapodagrionidae (5). The occurrence of members of the families Megapodagrionidae, Chlorocyphidae and Calopterigididae indicates that the stream ecosystem can sustain species with narrow niches. Seven physico-chemical variables: temperature (water and ambient), pH, turbidity, electrical conductivity, dissolved oxygen, water current velocity and depth of the stream were examined and analysed. Analysis of variance (ANOVA) result revealed that conductivity, temperature and water depth played a major role in determining the community structure of odonate assemblage in the stream. The mean () standard deviation of electrical conductivity (184.25 6.37?S/cm) of the water was indicative of an unpolluted freshwater system with stable habitat structure. The study suggests that the water quality of Alatori stream is healthy and can sustain Odonata and other fauna within the ecosystem.