THE ECOLOGY AND DISTRIBUTION OF GRASSHOPPERS IN GHANA

Authors


Abstract

From 1957 to 1959 collections of grasshoppers were made in various parts of Ghana where the vegetation shows considerable variation from the evergreen forest of the south-west to the Sudan savanna of the north-west and north-east. Collections were made at intervals throughout the year in as many different localities as possible and as a result of these and earlier collections 196 species in 113 genera are now known from Ghana. Notes on the ecology and distribution of these species are given. The state of development of ovaries indicated that most breeding occurred during the wetter times of year and this was true even in the forest where conditions were always moist. Most species bred continuously in the south, but in the northern savanna with its long dry season breeding was more restricted and many species survived the dry period as immature adults. In completely undisturbed forest no grasshoppers were found, but there was a specific fauna, mostly of brachypterous species, along paths and in clearings. These were mostly Catantopinae whereas in the grasslands Acridinae and Truxalinae comprised a large part of the grasshopper fauna. Examination of the crop contents showed that all the Pyrgomorphidae and most Catantopinae were forb feeders while the Acridinae and Truxalinae mainly ate grass.

Summary

From December 1957 to August 1959 a study was made of the Ghana grasshoppers. Brief accounts of the climate and vegetation are given, followed by notes on the distribution, seasonal occurrence and breeding of the grasshoppers. In all 128 species belonging to ninety genera were recorded.

Many species continued to breed throughout the year but breeding increased during the rainy season. This appeared particularly true of the northern savanna regions, where very few were breeding in January, but it was also true in the south, including the forest. In the north many species apparently had an adult diapause over the dry season, but in the south, with no marked dry season, breeding was more continuous. A few species had only a single annual generation.

A few species, mostly brachypterous, were characteristic of the forest and others of the adjacent thicket regions. These were nearly all Catantopinae. Many more species occurred in the savanna and the southern grass plains and about half of these were Acridinae or Truxalinae. Fifty-four species were common to northern and southern grasslands; thirty-three were confined to the north and twenty-six to the south. Other species were widespread, but local, characteristically being found near water or in cultivated areas.

The food eaten by the grasshoppers was classified as grass or forbs by examination of the crop contents. All the Pyrgomorphidae and most Catantopinae fed on forbs while most Acridinae and Truxalinae ate grass. A few Catantopinae fed indiscriminately on grass or forbs and amongst these were some of the most widespread species.

There was some tendency for species to be greener during the rainy season than at other times and black specimens were often associated with burnt areas. The gregarious nymphs of Phymateus were black and yellow.

A few records are given of parasitism by mermithids and dipterous larvae and of predation by insects, birds and reptiles.

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