Notes on East African bush locusts with special reference to Phymateus aegrotus, Gerstaecker 1869 (Orth., Acrid., Pyrgomorphinae).

Abstract

The term “Bush Locust” is defined.The synonymy and known distribution of Phymateus aegrotus are given and previously published records of its occurrence are reviewed.The occurrence of hopper-bands, and of adults, in East Africa for the years 1938–47, inclusive, is outlined.P. aegrotus and other species of the genus are normally unimportant economically as adults, but the hoppers form bands after the manner of, though on a much smaller scale than, true locusts. Outbreaks of these hopper-bands appear to be sporadic but they are sometimes destructive to crops.P. aegrotus has usually been of only local importance as an agricultural pest but areas in which the crops have been damaged are noted. Among wild host-plants there appears to be a preference for Euphorbiaceae although the hoppers are more or less polyphagous.Other East African species which form hopper-bands and which are known to attack crops are mentioned.The life-history of P. aegrotus is described so far as it is known, and observations made by Dr. H. B. N. Hynes on the closely related species, P. pulcherrimus, in Ethiopia are also recorded.Reflex actions in Phymateus species, including such phenomena as autohaemorrhage and colour display by the adults when alarmed, are noted and the literature on the subject is reviewed.Observations are made on hopper behaviour and band-size of P. aegrotus. The latter is usually only a square yard or two in extent but bands up to 25 square yards in area have been observed by the author and there are reports of even larger ones. These bands are very dense both when marching and when stationary (60–80 finalinstar hoppers per square foot). Notes on areas of infestation are also given.In most cases it is sufficient to beat out the bands with branches. Poison bait and dusting with 7 per cent, di-nitro-ortho-cresol are also successful.Detailed descriptions of the coloration of final-instar hoppers of P. aegrotus and the other East African Phymateus species discussed are given. Keys for the identification of these hoppers and of the adults of the four species, P. aegrotus (Gerst.), P. pulcherrimus I. Bol., P. viridipes Stål and P. purpurascens Karsch (for all of which standardised English names are proposed), are also included.