Influence of Seasonality and Eucalyptus Plantation Types on the Abundance and Diversity of Litter Insects at the Arboretum of Ruhande in Southern Rwanda

Abstract

The aim of this study was to document on the influence of seasonal variability and Eucalyptus plantation types on the abundance and diversity of litter insects using the Arboretum of Ruhande in Rwanda. Insect individuals were sampled and fixed in a 10% formalin solution, and brought to the laboratory for identification to order and family levels. Insect individuals were classified in 9 orders and 27 families. Coleoptera and Hemiptera orders were the most diversified with eight families each. The results indicated that the order Hymenoptera showed the highest abundance in all seasons, followed by Coleoptera, Hemiptera, and Isoptera orders. Results indicated that stands of four Eucalyptus species have litter insect diversity which was higher than that of native Entandrophragma excelsum which was set as a reference. Insects abundance combined with Shannon diversity indices in different seasons indicated that stands of Entandrophragma excelsum, Eucalyptus grandis, Eucalyptus maidenii and Eucalyptus saligna have the best conditions for the establishment of diverse insects in the litter. Therefore, negative ecological effects of Eucalyptus species on insect biodiversity may not be exclusively attributed to the whole genera. Seasonal variation of litter insect diversity indicated that dry season (September 2012) had the highest Shannon diversity indices relative to those in rainy seasons (January and April 2013). This indicates that heavy rain negatively impact the survival and diversity of litter insects. High variability of litter insects is attributed to the variability of habitat conditions, including understory vegetation, litter cover, and soil chemistry. Further studies on seasonal variation of litter insects in other Rwandan ecological regions are needed.

Keywords: Entandrophragma; Eucalyptus; Insects; Hymenoptera; Seasonal variation.