Some East African Species of Lygus, with Notes on their Host Plants

Extract

In my recent paper on “Lygus simonyi, Reut., as a Cotton Pest in Uganda”*, I referred in the introductory notes to the fact that I had studied the male genitalia and other characters of about 20 species of Lygus in order to determine reliably all specimens collected in the course of the field work on which I was then engaged. In the present paper all of these species are described. Only a few of them occur commonly on cotton, and only one, which must now be called L. vosseleri, Popp., is a major pest of cotton, but the others were encountered, in most cases very frequently, in connection with an investigation of the alternative host plants of the cotton-frequenting species, and two are common on coffee (with L. coffeae, China, which belongs to a different group of species and is therefore not included here). Some of them bear a very close resemblance to L. vosseleri and often occur with it on the same plants and in the same localities; consequently considerable confusion had existed previously as to the identity of the various species collected.

In connection with field work it is often necessary to identify large numbers of specimens rapidly and without adequate facilities for the examination of genitalia. Consequently, the object of my study of the external genitalia of the males was not only to separate the species on the basis of these structures but also to test by means of them the reliability for diagnostic purposes of the few differences, such as those of colour and markings, that occur in both sexes and are readily visible with a hand lens. I concluded that the male genitalia afford the best characters for determination whenever they can be examined, but that colour and markings can suffice in both sexes for this purpose, despite the great variation which occurs in most species. The only other characters that are of value for the separation of species, within the group with which I have dealt, are size and (occasionally) length of rostrum. There is, in fact, a remarkable uniformity throughout this species group, so that in the absence of males or of facilities for examining genitalia, determination must depend upon a combination of a few simple characters, two of which, colour and markings, are variable, often difficult to describe, and can be utilised satisfactorily only after experience has been gained of many species and specimens from numerous localities and plants.

The species described in this paper constitute what may be called the simonyi group of Lygus and have the following features in common:—

1. A smooth, semi-shiny appearance (never very shiny because of slight pubescence and minute punctation).

2. The whole of the dorsal surface, including the hemelytra, and also the ventral surface, rather sparsely covered with very fine, short decumbent hairs directed backwards.

3. The whole of the dorsal surface, including the hemelytra, indistinctly and minutely punctate; the scutellum and (to a lesser extent) the pronotum very slightly rugose transversely.