Distribution and Abundance of Insect Orders in relation to Habitat types in Opa Stream-Reservoir System, Nigeria

Abstract

Aquatic insects collected from the stream below the dam, the pool and the spillway of Opa stream-reservoir system in Ile-Ife, Nigeria, were compared. The primary purpose of this collection is to carry out an assessment of the relation between habitat structure and the distribution and abundance of aquatic insects in the water body. There was a marked difference in the taxonomic composition of insects in the spillway from those in the pool and stream. Only the larvae of the Trichoptera family, Hydropsychidae were present in the spillway while Ephemeroptera, Odonata, Plecoptera, Coleoptera, Hemiptera and Diptera occurred in the other sampling locations. Jaccard's similarity index and similarity ratio were 0.667 and -1.09 respectively, when the taxa composition and insect abundance from stream and pool were compared. This indicates that both sampling locations are considerably similar. The Trichoptera larvae occurred in large numbers and closely associated with a moss, Fontinalis (Bryophyta), recording 1232.5, 900 and 1178 larvae per sq.m as densities in August, September and November respectively. With Trichoptera larvae alone, the spillway recorded the highest total number of individuals among the three sampling locations throughout the period of study. It was inferred that Fontinalis provided strong foundations for larvae, refuge from predators, and substratum for algae and diatoms which serve as food resource for larvae. The moss - Trichoptera association in an unstable habitat such as the spillway was discussed with reference to the ability of hydropsychid caddisflies to survive in a wide range of habitats. However, the association observed in this study needs further investigation. Journal of Aquatic Sciences Volume 16, April 2001, pp. 7-12 KEY WORDS: Bryophyta, Fontinalis, reservoir spillway, Trichoptera, Insecta, habitat preference.