Ixalidium bicoloripes Uvarov, 1941

Ixalidium bicoloripes Uvarov, 1941 View in CoL

( Fig. 5B; Table 6)

Ixalidium bicoloripes Uvarov, 1941: 28-30 View in CoL .

TYPE MATERIAL EXAMINED. — Holotype. Kenya • ♂; Emali Range , Sultan Hamud; 4 900-5 900 ft a.s.l.; 13.III.1940; V. G. L. Van Someren leg.; NHMUK.

Paratypes. Kenya • 2 ♂, 2 ♀; same collection data as for preceding; NHMUK .

OTHER MATERIAL EXAMINED. — Kenya • 1 ♂; Machakos District, NNE of Emali, Nzaui Hill ; 1°55’S, 37°33’E; 5900 ft a.s.l.; 26.I.1990; J. M. Ritchie & M. N. Mungai leg.; mature pine plantation forest; NHMUK GoogleMaps .

MEASUREMENTS. — Table 6.

DISTRIBUTION

Ixalidium haematoscelis is known from the Taita Hills and Sagala, Kenya. The same or closely related species occur in riverine forest near Kibwezi, in the Chyulu Hills and on Kilibasi Hill. Ixalidium sjostedti is found on the slopes of Mt Kilimanjaro and Mt Meru, Tanzania, in forest and montane grassland up to 1660 m a.s.l. Closely related species, as yet undescribed, occur in the North and South Pare Mountains. Ixalidium bicoloripes is known only from the Emali Hills, but it has not been collected since 1941 and the exact type locality is unidentified. Similar specimens are known from Nzaui Hill and from the northern foot slope of Mt Kenya.

REMARKS

The male genitalia of Ixalidium sjostedti Kevan ( Fig. 11) are closely similar to those of I. haematoscelis ( Fig. 10) and other undescribed putative species of Ixalidium . The genitalia of I. bicoloripes are not available for study, but examination of material from other mountains in Kenya suggests they will also be closely similar. The genitalia of Ixalidium have numerous similarities with those of Mazaea and Barombia but are radically different from those of Tangana and Rowellacris Ritchie & Hemp n. gen., as well as being conspicuously smaller and more slender than those of any other genus in the family. In fact, each of the three East African genera, while individually consistent, is quite distinct from the others.

Gerstäcker’s male syntype of Ixalidium haematoscelis is not available for dissection, but the identity of the species is not in doubt as there is only one species of this family present in the Taita Hills. The genitalia erroneously figured for I. haematoscelis by Dirsh (1966) were in reality those of an undescribed species of Rowellacris Ritchie & Hemp n. gen. from the East Usambara Mountains, while the specimen

I. haematoscelis Gerstäcker, 1869 View in CoL I. bicoloripes Uvarov, 1941 View in CoL

Size slightly smaller [than I. bicoloripes View in CoL ]; very slightly larger – [than I. sjostedti View in CoL ] ( Kevan 1950).

Fastigium of very slightly narrower [than I. bicoloripes ]; rather wider almost twice as wide as its length (males), more than vertex [than I. sjostedti ] ( Kevan 1950). twice as wide as its length (females) ( Uvarov 1941); wider than I. haematoscelis ( Uvarov 1941: 29) .

Hind tibiae colour almost wholly red, becoming brownish in basal third (Uvarov brownish black in basal half and red in the apical half 1941: 28); less extensively and less intensely dark basally [than ( Uvarov 1941: 28-29). I. bicoloripes ] ( Kevan 1950).

Puncturation of finer [than I. bicoloripes ] ( Kevan 1950). head, pronotum and abdomen coarsely punctured integument and rugose; punctures and rugosities becoming less pronounced posteriorly ( Uvarov 1941).

Abdominal differs from I. sjostedti in the gibbose [swollen] abdominal terga; abdominal tergites gibbose in profile; median carina tergites less gibbose abdominal terga than I. bicoloripes ( Kevan 1950) . acute throughout, distinctly convex in profile on each segment ( Uvarov 1941).

Last abdominal differs from I. bicoloripes in trapezoidal excision of the last with a broad and deep incision ( Uvarov 1941).

tergite abdominal tergum ( Kevan 1950).

Male supra-anal basal portion less broad than I. bicoloripes , with straight sides, very long and acute, basal part wider than long, with plate apical portion less acutely pointed than I. bicoloripes (Uvarov pair of very irregular rugose ridges parallel to middle 1941); wider than I. sjostedti , though more acutely pointed; line; apical part acutely triangular, distinctly longer basal portion slightly narrower than I. bicoloripes ; apical portion than its basal width ( Uvarov 1941). slightly shorter with straight (not slightly concave) sides and more distinct median sulcus than I. bicoloripes ; impression on base narrower and better defined than I. bicoloripes , being a sulcus rather than an impression between two widely spaced ridges ( Kevan 1950).

from Jadini Beach , Kenya, figured by Johnsen & Forchhammer (1975: 41, figs 15-18) as representing I. haematoscelis View in CoL , probably belongs (as they suspected) to Rowellacris obscuripes ( Miller, 1929) n. comb.

To our knowledge the supplementary apodemes of cingulum found in Ixalidium View in CoL ( Fig. 11B, C), Mazaea View in CoL and Barombia View in CoL have not previously been described in Acridoidea, though they were faithfully illustrated by Dirsh (1966) in Mazaea View in CoL and Barombia View in CoL . These additional muscle attachment points presumably enhance manoeuvrability of the exserted genitalia during mating in species with relatively weak apodemes of cingulum. The medial section of the endophallus is apparently very flexible in life, as dissected specimens have been found to exhibit widely differing angles between the basal valves and the aedeagus, especially in Mazaea View in CoL . The alternating bands of more and less sclerotised cuticle visible ventrally at the base of the middle section of the endophallus ( Fig. 7F; 9D; 11B, D) may facilitate this flexibility.

At present we are not able reliably to separate the described species of Ixalidium morphologically, hence no key or differential diagnosis is offered here. Kevan (1950: 211) and Uvarov (1941: 28-29) attempted to distinguish I. sjostedti and I. bicoloripes , respectively, from I. haematoscelis on the basis of minor features of the sculpturing, coloration, abdominal profile, supra-anal plate morphology and size ( Table 7). Comparison of measurements of available material ( Tables 4; 6) indicates that the size range and bodily proportions of different populations overlap. Hind tibial colour also varies within populations. Nonetheless, the shape of the subgenital plate, though variable, does appear to differ between species ( Fig. 5 A-C). In general I. haematoscelis has a somewhat wider and shorter apical section of the supra-anal plate than the other described species, but this has not been assessed with large samples. From molecular evidence (unpublished data) it appears probable that the three described species are all valid and that widely separated populations of Ixalidium found in different mountainous areas of east Africa, including the North and South Pare Mountains, Mt Kasigau (a mountain adjacent to the Taita Hills) and Mt Kenya may represent closely related species.