Diversité et distribution des Tetrigidae (Orthoptera : Caelifera) dans quelques Régions de la partie sud du Cameroun

Abstract

Tetrigidae are mainly forest dwellers and often hygrophilous; they are relict Orthoptera known since the cretaceous period. They are cosmopolitan and belong to the infraorder Acrididea. Most species of Tetrigidae feed on small size plants, especially mosses, single celled algae, detritus and simultaneously swallow sand and lot of humus. They are good indicators of the health state of terrestrial ecosystems. In temperate zones, they are associated with perennial habitats in intensive agriculture areas. The loss of native forest habitat due to various development projects constitutes a significant threat to the survival of many species. This affects the structure of the forest and therefore alters the richness and abundance of species that may be threatened with extinction. Faced with the observed degradation of the natural environment in Cameroon, it is difficult to develop effective conservation actions without mastering certain aspects of the bio-ecology of Tetrigidae. The general objective of this work was to determine the diversity and distribution of Tetrigidae in the southern part of Cameroon. The specimens were collected in three Regions (Centre, West and South-West) particularly in nine localities (three localities per region) from February 2016 to February 2018. In each locality, four plant landscapes, namely forests, agro -forests (cocoa or coffee trees), fallow land and crop fields were surveyed. In each landscape, two methods of capture were used: sweep net and ―pitfall‖. The study allowed us to identify 1300 individuals belonging to 24 species, 12 genera and 2 subfamilies (Cladonotinae and Tetriginae). The Cladonotinae subfamily includes 4 subspecies and 4 species belonging to 6 genera, while the Tetriginae subfamily comprised 16 species and 6 genera. An identification key of the species constituting the Tetrigidofauna of these three studied regions was setup. The phenetic analysis conducted from Neighbour Joining supported the monophyly of Tetrigidae (100% Boostrap). The West Region was the richest in species (20 species), followed by the Center Region (17 species) and finally the South West Region (8 species). The highest number of Tetrigidae species was noted during the rainy season (16 species), compared with 7 species in the dry season. The "pitfall" captured twice as many species of Tetrigidae (24 species) as the sweep net (12 species). Sampling success was higher during rainy and dry seasons in the Southwest with the Chao1 estimator (100%). The lowest success was observed during the dry season in the West with the ICE estimator (53.01%). Biological diversity varied greatly between regions, localities, landscapes, capture methods and seasons. Most species were constant and accessory. Overall, 70.83% (17 species) of species had an aggregated distribution, 12.5% (3 species) of species had a random distribution, and the remaining 16.67% (4 species) of species showed a more regular distribution. We had 21 and 12 species xxx that were potentially bio-indicators respectively for types of vegetation and the types of seasons. As for the seasons, 02 and 01 species respectively were indicator for the rainy season and the dry season respectively. 02, 01, 01, 01 species were really bio-indicators respectively in agro-forests, forests, open environments (crop fields and grassy fallows) and closed environments (agroforests and forests). The results obtained from the present study are of paramount importance for future environmental monitoring studies and research dedicated to conservation of species or the planning of the national territory. They also constitute a major contribution to the inventory of the Tetrigidofauna of the three studied regions in Cameroon. Finally, this represent an updated database for the knowledge of this group of organisms among the Orthoptera whose studies seem to be neglected by African entomologists.