Recent Investigations of Two New Tree-Borers in the Indigenous Forests of East Africa (O.D.C. 453)

Summary

Ioberlinia scheffleri Harms is a common tree in the East Usambara Mountains of Tanganyika, and Parinari excelsa subsp. holstii is the dominant tree of the Kalinzu Forest and adjacent areas of Uganda. The utilization of these two species, however, is severely curtailed by borer damage. The infestations to which the living trees are subject, results in serious losses in volume on conversion and frequently renders trees unacceptable for milling. In certain areas of the Usambaras 87 per cent of all commercial size Isoberlinia trees are borer-infested. In parts of the Kalinzu concessions 98 per cent of exploitable Parinari trees are attacked.

The insects responsible are both Lamiidae, which are new to science and have only recently been obtained and identified. The Isoberlinia borer is a species of Prosopocera and the borer of Parinari is gen et sp incog of or near the tribe Xylorhizini. The author's observations on the general habits of these species, represent the first contribution to the elucidation of their biology and are summarized in this paper. Some of the more unusual features of the borers are emphasized, and tentative explanations are given to account for certain aspects of their biology. From the results of biological studies and a census of borer incidence, it is concluded that in certain areas of East Africa it would be futile to encourage the future regeneration of Isoberlinia and Parinari. It is suggested that these should be eliminated in favour of other species, which are equally useful as timber and which are free from borer attack.