Studies on Insect Diversity and Abundance at Belette-Gera Forest, South Western Ethiopia

Belette-Gera Forest is one of the Afromontane rain forests in south western Ethiopia. The diversity and abundance of insect communities within the forest are not studied and there is no documentation of the insect fauna of the forest.Iinsects is ecologically important and play valuable role in the ecosystem of Belette-Gera forest. This study identified insect species within the forest and assesssed thier diversity, abundance and distribution among habitats and seasons. Habitat distribution of insect fauna was catagorized into three habitats having different land uses/cover and varying degrees of disturbance; Natural forest habiat, Plantation forest habitat and Wetland habitat. Seasonal distribution of insect fauna was also studied in three seasons; long rain season, long dry season and short rain season. Insect species richness and abundance of insect communities of Belette-Gera forest was investigated along a line transect of 100m × 100m starting from the bottom of the valley to the top of the ridge with sample quadrats of 10m ×10m laid for sampling insects. A total of 1560 insect specimens from 14 orders and 120 families were collected from September 2013 to August 2015 using sweep net trap, beating cloth, pitfall trap and hand picking. Shannon-Wiener diversity index and Evenness were used to measure diversity and abundance of the insects at the family level. The highest insect diversity was observed in the order Coleoptera with Shannon diversity index, Hʹ value of 1.77 and evenness, E value of 0.37. Dermaptera, Ephemeroptera, Mecoptera and Neuroptera were the raret insect orders. Similarly, diversity was measured in each habitat III using Shannon-Wiener species diversity index and Evenness. A total of 620 specimens (39.74 %) in the Natural forest habitat, 472 specimens (30.26 %) in the Wetland habitat and 468 specimens (30 %) in the Plantation forest habitat, were collected. These insects were used to determine the richness of the insect fauna in each habitat type. The highest insect diversity was observed in the Natural forest habitat with (Shannon’s, Hʹ= 2.36) and (Evenness, E = 0.49) followed by Plantation forest habitat (Hʹ= 1.84; E = 0.38) and the lowest were recorded in the Wetland habitat (Hʹ= 1.78; E= 0.37). In addition, the influence of season on the diversity and abundance of insects was computed for two different years (2013/2014 and 2014/2015). Shannon-Wiener species diversity index (H’) and Evenness (E ) were used to measure species diversity and abundance in each season. Paired sample T test was computed to determine the significant differences in insects collected in the rainy and dry seasons. Insect abundance and diversity were significantly different between seasons and in 2013/2014 the highest diversity was recorded in the long rain season with (Hʹvalue of 2.563; E value of 0.563). On the other hand, the lowest diversity was recorded during the short rain season (Hʹ value of 1.234; E value of 0.271). Furthermore, in 2014/2015 the highest diversity was recorded in long rainy season with Shannon’s Hʹvalue of 1.868 and with E value of 0.417. The lowest insect diversity was recorded from short rainy season with Shannon’s Hʹ value 1.57. The diversity and abundance of insect communities varied with respect to habitat type and season. As a result, Wet land habitat, Plantation forest habitat and Natural forest habitat were varied in increasing order with respect to diversity and abundance of insect communities. In addition, Short rainy season, Long dry season and Long rainy season varied in increasing order with respect to of diversity and abundance in the study forest. The variation of insect species diversity and abundance in the habitat types and seasons were the result of IV environmental variation (both biotic and abiotic factors), human interference; and the responce of insects to thesef actors influenced the diversity and abumdance of insect communities residing in these habitats in different seasons. Therefore, knowledge on the identity of insect species and factors which influence their diversity and abundance is important as baseline information for further study to assess the different aspects of the insect founa adapted in Belette-Gera forest.