Ecology of Aquatic Insects in Opi Lake, Enugu State, Nigeria.
ABSTRACT
The ecology of aquatic insects of Opi Lake was carried out to determine their composition, abundance and diversity from February to July, 2014.
Adult insects of different species were collected from the water surface using a dip-net with Nytex® netting of 500µm mesh.
In addition, adult Insects and nymphs were collected from the vegetation around the lake using a sweep net with mesh size of 250µm, while bottom dwellers were sampled using a scoop net.
The lake was divided into three sampling stations as a result of the nature and amount of the vegetation, and the type of substratum found in each location. Station 1 had vegetation, shade and detritus, Station 2 had no shade, very little detritus and vegetation, while Station 3 had shade, detritus with no vegetation.
The physico-chemical parameters and heavy metals concentrations of the lake were determined while the climatic data of the area was collected from the Center for Space Science University of Nigeria Nsukka.
A total number of 1,042 insects representing 30 species, belonging to 26 families and 8 orders were recorded. Odonata had the highest mean abundance (44.52%) in all the stations, followed by Hemiptera (23.32%) which was the most diverse group.
Hemiptera had the highest number of families (8 out of the 26 families collected). Other insect orders collected with their abundance include: Coleoptera (12.28%), Orthoptera (10.29%), Hymenoptera (5.09%), Diptera (3.36%), Trichoptera (1.06%) and Lepidoptera (0.01%). Station 1 recorded the maximum number (46.35%) of aquatic insects throughout the sampling season.
However, stations 2 and 3 recorded 28.98% and 24.66% of aquatic insects respectively. The abundance of insects was maximum in the month of July (20.44%) and minimum in April (8.16%).
The abundance and distribution of insect species varied and were not constant from one month to another during the period of study, due to biotic and abiotic factors.
There was high species diversity of aquatic insects in the different strata of the lake, indicating the rich and diverse group of insects in the study area. Dissolved Oxygen had an inverse relationship with Orthoptera (r = -0.63, p < 0.01) and Hymenoptera (r = -0.54, p < 0.05.
Diptera also had negative relationship with depth (r = -0.48, p < 0.05). There was positive correlation between Hemiptera and Copper (r = 0.78, p < 0.01), while Iron also correlated positively with Coleoptera (r = 0.47, p < 0.05) and Lepidoptera (r=0.59, p < 0.05).
Among the insects and zooplankton, Odonata had positive correlations with Rotifera (r=0.502, p < 0.05), Cyclops (r = 0.541, p < 0.05), Bosmina (r=0.53, p < 0.05) and Daphnia (r = 0.595, p < 0.01).
Orthoptera also showed positive relationship with Fish egg (r = 0.684, p < 0.01). Also, with phytoplankton, Odonata had positive relationship with Chlorophycaea (r = 0.505, p < 0.05) and Xanthophycaea (r = 0.499, p < 0.05).
Orthoptera correlated positively with Cryptophycaea (r = 0.491, p < 0.05) and Xanthophycaea (r = 0.487, p < 0.05).This therefore, adds to the fact that undisturbed habitat quality is more suitable for insects to breed and multiply under the natural ecosystem with abundant food supply.
TABLE OF CONTENTS
Title Page………………..i
Approval Page……….ii
Dedication……………iii
Acknowledgement……iv
Table of Contents…..vi
List of Tables …ix
List of Figures..x
List of Plates…..xii
Abstract……..xiii
Chapter One: Introduction and Literature Review
1.1 Introduction………..1
1.2 Justification of the Study…….3
1.3 Objective of the Study……….4
1.4 Literature Review…….4
1.4.1. Some structural adaptations of insects in the aquatic community….6
1.4.2. Major groups of aquatic insects………….8
1.4.3. Insect taxonomic diversity ………..12
1.4.4. Factors affecting the distribution and abundance of insects in aquatic environment……..13
1.4.5. Biological constraints on aquatic insects (role of biotic factors in the distribution and abundance of aquatic insects)…17
1.4.6. Substrate Type……….19
1.4.7. Activities and ecological role of adult aquatic insects…….19
CHAPTER TWO: MATERIALS AND METHODS
2.1 Study Area…………23
2.2 Meteorological Data…………25
2.3 Aquatic Insects Sampling………25
2.4 Identification of Insects………..26
2.5 Determination of Physico-chemical Parameters………26
2.6 Macroinvertebrate Sampling……..29
2.7 Plankton Sampling…….30
2.8 Statistical Analysis……….30
CHAPTER THREE: RESULTS
3.1 Meteorological Data of Study Area……………31
3.2 Aquatic Insects Sampling and Identification….41
3.3 Mean Monthly Abundance of Aquatic Insect Orders in Opi Lake……43
3.4 Correlation Matrix of the Relationship between Aquatic Insects Abundance in Opi Lake…45
3.5 Mean Monthly Value of the Physico-chemical Parameters of Opi Lake…..51
3.6 Correlation of physico-chemical parameters/ Heavy Metals and Aquatic insect orders…53
3.7 Mean Monthly Composition and Abundance of Zooplanktons in Opi Lake….59
3.8 Mean Monthly Composition and Abundance of Phytoplanktons of Opi Lake………….62
3.9 Mean Monthly Composition and Abundance of Macroinvertebrates in Opi Lake………64
3.10 Correlation of Aquatic Insects and Zooplanktons of Opi Lake….66
3.11 Relationship of Aquatic Insects and Phytoplankton of Opi Lake..70
3.12 Relationship of Aquatic Insects and Macroinvertebrate in Opi Lake………74
CHAPTER FOUR: DISCUSSION AND CONCLUSION
4.1 Discussion………..78
4.2 Conclusion……….84
REFERENCES
INTRODUCTION
Aquatic habitats are known to accommodate a great number of the earth’s arthropods. These include insects, many of which are known to utilize the aquatic ecosystem in various ways, and sometimes only at certain stages of their life cycle (Pennak, 1978; Voshell, 2002).
Insects are very successful in aquatic ecosystem, especially the freshwater environment. This is demonstrated by their diversity, abundance, broad distribution and their ability to exploit most types of aquatic habitats.
The importance of these organisms range from their provision of support to terrestrial lives through aquatic maintenance of food chains to serving as indicators of water quality due to their varying tolerance limits to organic and inorganic substances (Bass, 1994; Mason, 2002).
There are about 751,000 known species of insects, which is about three-fourths of all species of animals on the planet. Most insects live on land; their diversity also includes many species that are aquatic in habit (Westfall and Tennessen, 1996).
Freshwater makes up only about 0.01% of world total water body and contains about 100000 species (8%) out of 1.3 million scientifically described species (Dudgeon, 1999).
Aquatic insects are extremely important in ecological systems for many reasons (Merritt et al., 2008) and are the primary bio-indicators of freshwater bodies such as lakes, ponds, wetland, streams and rivers.
They serve various purposes such as food of fishes and other invertebrates, as vectors of pathogens to both humans and animals (Foil, 1998; Chae et al., 2000).
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