Abundance and diversity of insects associated with Rhizophora mangle and Avicennia germinans in Bundu-Ama mangrove ecosystem of the Niger Delta, Nigeria

Mangrove species diversity is well known for larger animals and plant, but little is known about mangrove insects and their significance and yet they perform important roles in the ecology of the habitat. The present study was conducted to determine the diversity of insects associated with Rhizophora mangle and Avicennia germinans in Bundu-Ama mangrove habitats, a tributary of the Bonny River in the Niger Delta. Two stations were established based on the abundance of the mangroves. A total of 18 mangrove trees (nine each) for both species were randomly selected and insect samples collected bi-weekly between 7 am and 11 am between April and June 2017, making a total of 108 trees within the study period. Each tree was sampled for 10 minutes using sweep net, hand net and handpicking methods. A total of 8 insect orders (Diptera, Coleoptera, Hymenoptera, Homoptera, Rhopalocera, Odonata, Phasmida and Heterocera), 20 families and 35 species were identified. Hymenoptera (49.1%) was the highest insect order recorded, followed by Diptera and Homoptera. Avicennia had more insect orders, families and species. Coleoptera, diptera and Hymenoptera were found on both plants while others were on Avicennia only. Formicidae was the most abundant family (37.1%) while Lagiidae was the least (0.2%). The most abundant species was Camponotus acvapimenis. The highest species diversity was observed in the Diptera with Shanon H’ of 2.00 for Avicennia and 2.13 for Rhizophora. The richness index was 2.43 for Avicennia and 2.62 for Rhizophora, and the highest species evenness (E’= 0.40) was observed in the Diptera indicating that the insects were not evenly distributed. Two insect associations were identified: a specialist group of 23 species on Avicennia, and 6 species on Rhizophora, while the second group were the generalist made up of 3 species Anopheles squamosus, Musca domestica and Fannia sp. Insect families (Muscidae, Calliphoridae, Syrphidae, Ceratopogonidae, Culicidae, Tabanidae) are of medical, veterinary and ecological importance as pollinators, bioindicators, predators, parasitoid, agricultural pest and detritivores. Insect diversity was found to be higher in Avicennia than in Rhizophora. This study has shown that the mangroves of Bundu-Ama have a vast array of insects which will contribute to their biodiversity data and subsequent conservation and management of ecosystem in the Niger Delta.