Simulium (Byssodon) buxtoni Austen, 1923

Crosskey, R. W., 2002, A taxonomic account of the black y fauna of Iraq and Iran, including keys for species identi cation (Diptera: Simuliidae), Journal of Natural History 36 (15), pp. 1841-1886 : 1858-1863

3. Simulium (Byssodon) buxtoni Austen

Simulium bipunctatum Austen, 1923: 275 . Holotype, Iraq (‘Mesopotamia’) (BMNH) [examined].

Simulium bipunctatum var. buxtoni Austen, 1923: 276 . Holotype, Jordan (‘Palestine’) (BMNH) [examined].

Simulium (Nevermannia) bipunctatum Austen : Rubtsov, 1940: 357 (rst subgeneric placement). Simulium irakae Smart, 1944: 134 , [unnecessary] substitute name for Simulium bipunctatum

Austen (junior primary homonym of Simulium bipunctatum Malloch, 1912 ). Eusimulium bipunctatum (Austen) : Rubtsov, 1956: 487 (rst use of combination). Eusimulium irakae (Smart) : Rubtsov, 1962a: 359 (rst use of combination). Simulium (Psilocnetha) irakae Smart : Crosskey, 1967: 37 (revised subgeneric placement). Simulium (Byssodon) buxtoni Austen : Crosskey, 1969: 47, 48 ( Psilocnetha synonymized with

Byssodon , revised subgeneric placement, buxtoni established as having validity over irakae ). Byssodon irakae (Smart) : Rubtsov and Yankovsky, 1984: 87 (rst use of combination, buxtoni

incorrectly listed as invalid).

Iran references. None (citation ‘Iran’ in Rubtsov and Yankovsky, 1984, error for Iraq).

Iraq references (excluding nomenclatural changes, see above). Khalaf (1963, as irakae , list of Iraqi Diptera ), Crosskey (1967, discussion, redescribed, as irakae ), Abul-hab and Shihab (1980, provincial record, as irakae ), Abul-hab (1983, as irakae , new records), Rubtsov and Yankovsky (1988, Palaearctic catalogue as Byssodon irakae ), Crosskey (1988, world checklist entry), Crosskey and Howard (1997, world inventory entry).

Material seen

Iraq: HOLOTYPE of Simulium bipunctatum Austen , ‘ Mesopotamia’ [no other locality], 1921 (Fraser); paratypes 3, Mesopotamia, Baghdad Province, R. Tigris , Daurah (5Daura), 8 km S of Baghdad (33ss15¾/44ss26¾), May to June 1920; paratypes 5, data as holotype. 8, ‘ Mesopotamia’ , 1921 (Fraser). 6, Baghdad Province, Baghdad, in Babylon Hotel (33ss20¾/44ss26¾), May 1988 (Olejnicek). 29, Anbar Province, R. Euphrates , Khan al Baghdadi (5Al Baghdadi) (33ss52¾/42ss33¾), 2 July 1977 (Abul-hab). 11, Anbar Province, R. Euphrates , Al Hadithah (34ss09¾/42ss22¾), 2 July 1977 (Abul-hab). 14, ‘Middle Iraq’ [no other data].

Jordan: HOLOTYPE of Simulium bipunctatum Austen var. buxtoni Austen , ‘Palestine’, Jericho, 1 January 1922 (Buxton) ( BMNH). 8, of Simulium bipunctatum Austen var. buxtoni , ‘Palestine’, Jericho, 2 June 1922 (Buxton) ( BMNH) [specimens not mentioned by Austen (1923) and without type status].

Nomenclature

Some authors, as noted in the references cited above, have used the name irakae for this species but this name is invalid for an uncommon nomenclatural reason. When Austen (1923) described Simulium bipunctatum from Iraq he added a footnote (p. 276) brie y describing S. bipunctatum var. buxtoni from Palestine. The varietal name is available under the International Code of Zoological Nomenclature, having been proposed before 1961. The name bipunctatum Austen , however, is a junior homonym, being preoccupied by bipunctatum Malloch. Smart (1944) overlooked the nomenclatural implication of the name buxtoni and published the name irakae as a substitute name for Austen’s bipunctatum , whereas in fact the name buxtoni must (under the Code) come into valid use for the species concerned—provided the ‘variety’ is considered conspeci c with bipunctatum Austen. The name buxtoni was based on a unique female y (holotype) showing slightly darker legs than in Austen’s bipunctatum specimens from Iraq ( Mesopotamia) but no post-Austen author has recognized separate taxonomic status for buxtoni on this account. Hence Smart’s name irakae is invalid, an unnecessary substitute name, and buxtoni —having priority—is the valid name for the species ( Crosskey, 1988: 468).

New descriptive data

The aquatic stages of Simulium buxtoni are still unknown and only the female adult has previously been known and described. However, the material seen includes six alcohol-preserved male ies that were collected at lights in the Babylon Hotel, Baghdad (material listed above). Their condition is not good and they have faded to unnatural coloration through alcohol storage but it is possible here to provide a rst description of the adult male, emphasizing the structure of the genitalia as seen in slide preparations. I am also including information on the adult female to supplement my earlier redescription of this sex from the original material of bipunctatum ( Crosskey, 1967) .

Male. Very small y, wing length about 1.5 mm. Conforming, as, to primary characters of subgenus Byssodon as earlier de ned ( Crosskey, 1969), pleural membranes, katepisternum, postnotum and basal section of wing radius all bare. Legs pale yellow with darkened apices to femora and tibiae; hind tibia with trace of subbasal dark band (gure 97); hind basitarsus narrow and more or less parallel-sided in pro le (gure 97), about seven times longer than wide; calcipala and pedisculus (especially former) very well developed. Genitalia: gonopods with style almost as long as coxite, style in some views markedly billhook-like (gures 87, arrowed, and 94), shape changing to subrectangular as y is turned (gure 87), with one apical spinule; ventral plate saddle-shaped, without sharp keel, ‘shoulders’ distinctly sloping and side margins of plate somewhat convergent posteriorly (gure 93), basal arms slightly upcurved; parameres large, subtriangular, with heavy crescent-shaped sclerotization distally (gure 95); parameral spines massive, about six of varied size of which two spines much the largest (gure 96), spines in closed position lying along inner edge of paramere in tight backwardly directed group (gure 95); aedeagus slightly bilobed, armed with short strong thorny spicules (gure 95); median sclerite long and rod-like (gure 93).

Female (supplementary descriptive data). Frons wide. Middle antennal segments compacted and disc-like. Cibarium unarmed, its surface between cornuae smoothly concave. Terminalia: sternite 8 very well developed, somewhat boomerangshaped, its lateral parts long and tapering and well sclerotized (gure 99); ovipositor valves bluntly rounded and closely applied to each other, ovipositor notch between them slit-like (gure 100); each arm of genital fork tri d apically, bearing two widely divergent tapering processes (one directed inwards and other outwards) and a bluntly nger-like process directed upwards (gures 99, 100); paraprocts curving inwards ventrally towards each other, tapered to points that are only narrowly separated (gure 100); cerci in pro le with rounded apical ‘corners’ and subrectangular form (gure 98), dorsoventral height about three times as long as width at mid-point; spermatheca spherical, large for size of y (gure 100), diameter about 0.15 mm, without external surface structure and apparently without internal hair-spicules.

Remarks

Simulium buxtoni , an endemic species with unknown immature stages and occurring in the Euphrates and Tigris river valleys, has been very little studied even though its females are an irritant pest of humans ( Abul-hab, 1983)— especially where the Euphrates ows through Anbar Province of central Iraq north-west of Baghdad. The remarks given here collate what is known about the species under four subheads: aYnities, distribution, aquatic habitat and adult habits .

A Y nities. In the absence of knowledge of the aquatic stages, and (till now) the male y, the taxonomic placement of Simulium buxtoni has depended on the adult female. Austen (1923), in the original description (as bipunctatum ), observed that his new species was ‘not unlike the Nilotic S. griseicolle, Becker , of Upper Egypt and the Egyptian Sudan’, the lack of the pair of scutal dark spots in griseicolle being the stated diVerentiating character. Morphological characters of the male (description above), and better knowledge of the female terminalia, now permit more reliable assessment of how intimate the phyletic relationships of buxtoni and griseicolle might be. When examining buxtoni for my preliminary account of Middle East simuliids ( Crosskey, 1967) I concluded that the two species were certainly consubgeneric and placed them together in Psilocnetha Enderlein , afterwards ( Crosskey, 1969) subsuming this subgeneric taxon into the subgenus Byssodon . The latter was divided into two groups, the Holarctic S. meridionale species-group and the Afrotropical S. griseicolle species-group; S. buxtoni of the Middle East was left ungrouped on the basis that its position was not fully certain in the absence of the male and aquatic stages. Later, in my rst simuliid world checklist ( Crosskey, 1988), the species was listed in the S. meridionale species-group on grounds that a tentative group placement was better than leaving S. buxtoni in limbo. However, the males from Baghdad (listed above and received in 1988) changed the picture conclusively, since preparation of the genitalia showed that the male is virtually indistinguishable from that of S. griseicolle (see Freeman and de Meillon, 1953, for illustration of genital structures of this species). Simulium buxtoni must clearly be placed in the S. griseicolle speciesgroup of Byssodon , where it has recently been formally re-assigned ( Crosskey and Howard, 1997: 28).

Both sexes of the adults of S. buxtoni and S. griseicolle are so alike, except for the paired dark spots on the female scutum in buxtoni (gure 68), that the question might reasonably be asked—are they really separate species? Not only are the male genitalia more or less identical but the female terminalia also show no obvious diVerence. The female terminalia of S. griseicolle have the same conspicuously tri d genital fork arms (one of which is a blunt nger-like dorsal process like that of buxtoni in gure 100), the same strong boomerang-like sternite 8, and similar paraprocts drawn out to tapered points that almost meet in the midline of the venter— all of which features are clearly shown in the female terminalia illustration of Gibbins (1935) for S. griseicolle and have been observed by me in my own preparations. The large spherical spermatheca is also identical in the two species. All these facts indicate that further consideration should be given to the question of possible synonymy of S. buxtoni with S. griseicolle (nothwithstanding the scutal spot diVerence) once the larval and pupal stages of S. buxtoni and the chromosomal characteristics of both nominal species are known. Meanwhile, S. buxtoni is here considered a separate valid species.

The pupa of S. buxtoni when discovered will provide signi cant new information. In S. griseicolle the gill is comprised of three long tapered and attened branches like lanceolate leaves (gures in Gibbins, 1935; Freeman and de Meillon, 1953; Crosskey, 1969) and it is extremely likely that the gill of buxtoni will have the same general form. This is made the more probable by the fact that a long tri d gill also occurs in S. (B.) almae , a species of the S. griseicolle species-group described by Yankovsky and Koshkimbaev (1988) from Kazakhstan and the only other member of the group in the Palaearctic region. Judging from description (no material seen), however, S. almae is quite diVerent from the buxtoni / griseicolle species pair because the ventral plate margins are parallel (ru corne -like), the median sclerite is ared terminally, the spermatheca is ovoid rather than spherical, and the dorsal process of the genital fork is apparently absent (not shown in the illustration). The present conclusion concerning the aYnities of S. buxtoni must be that (1) it unequivocally belongs in the S. griseicolle group of subgenus Byssodon ; (2) separate speci city from griseicolle requires conclusive proof; and (3) it is not the same as the recently described species S. almae .

Distribution. The present-day geographical distribution of S. buxtoni is probably con ned to the middle Euphrates and Tigris valleys of central Iraq, though the possibility of its occurrence along the Euphrates within Syria cannot be ruled out in the light of its recent occurrence near the Iraq – Syria border (see below). It is almost certain that the species no longer occurs in ‘Palestine’, whence it was described from the Jericho type locality in 1922. The females from that site had probably emerged from the Jordan River, though because of the propensity for black ies to travel overland long distances as wind-assisted migrants ( Crosskey, 1990: 398–409, review) this cannot be assumed. Still, there is a gap of virtually waterless desert about 700–800 km wide between the Jordanian site and the ‘headquarters’ of S. buxtoni on the Euphrates, while Aswan in Egypt, the most northerly point of former distribution (and incidentally type locality) of S. griseicolle on the Nile is a similar distance from Jericho. On balance, local breeding sites on the Jordan is the most plausible reason for capture of the ies at Jericho. It is virtually certain, however, that such sites no longer exist on the Jordan today; substantial natural and man-made changes have aVected the water regime in this area of the Middle East since 1922, the Jordan being a regulated river, and none of the many collections of simuliids made in modern times in Jordan and Israel has resulted in the nding of any specimen of S. buxtoni in these countries or anywhere in the Middle East except Iraq.

The opposite is the case for Iraq, where modern collections have con rmed the existence of S. buxtoni in the Tigris river valley and along the middle Euphrates. The original females of S. bipunctatum (synonym of buxtoni ) were collected in 1921 at Daurah on the Tigris and nearly 70 years later (in 1988) males were caught in Baghdad (see material list above); probably breeding has been continuous in the river Tigris (the presumed source) throughout this time. No early records exist for S. buxtoni on the Euphrates river simply for lack of prospection, and the information now available is all from investigations carried out by Abul-hab (1983) in 1977; he collected females at villages and towns along the west bank of the Euphrates from Al Qa’im (34ss23¾/41ss11¾), near the border with Syria, downstream to Hit (5Heet) (33ss38¾/42ss50¾), a distance of some 250 km. Abul-hab also obtained ies at Al Fathah (35ss03¾/43ss34¾) and Ba’iji (34ss56¾/43ss29¾) on the Tigris in Salahaddin Province. In summary, the present-day geographical distribution of S. buxtoni lies within the co-ordinate limits 33–35ss50¾ North and 41–45ss East.

Aquatic habitat. Although the aquatic stages have not yet been found despite prospection of apparently suitable lotic habitat in the Euphrates ( Abul-hab, 1983) it is next to certain that the breeding places for S. buxtoni in the desert of central Iraq must be in the two great rivers of ‘Mesopotamia’, the Tigris and Euphrates; unlike S. ru corne and S. pseudequinum , it has not been found breeding in the desert oases, which clearly do not provide the right type of aquatic habitat. If S. buxtoni breeds, as must be assumed, only in the two large desert-traversing rivers, this is in line with the aquatic habitat preferentially selected by its close ally S. griseicolle , which is primarily a species of very large African rivers, especially the Nile.

The Euphrates runs moderately fast over (mainly) a bed of sand or pebbly gravel and would seem to oVer unsuitable bed substrate, unless perhaps—as Lewis (1948) found S. griseicolle willing to do in profusion in the Sudanese Nile — S. buxtoni pupates on hard river-bed mud. Ostensibly the many places in the ow of the Euphrates where it is partially impeded by submerged dikes to divert water to the irrigation water-wheels would seem to oVer substrate since they are built of rocks and stones; however, Abul-hab’s (1983) examination of such likely substrate proved negative, as also did his attempts to nd larvae and pupae on willow ( Salix ) twigs and leaves dipping into the current. ( Abul-hab (1983: 83) wrote that ‘in one place [Al Hadithah] only a few larvae were taken from the leaves of willow...’; however three larvae pertaining to this comment, when I examined them, were seen to be far too large to be those of S. buxtoni and appeared to be ornatum -group larvae. Confusion of vials and provenance is suspected: correspondence Abul-hab and Crosskey, October/ November 1982.)

It appears that nding the elusive immatures of S. buxtoni will be diYcult without using plastic ribbons or similar devices anchored in the current to act as larval substrate. Oviposition is likely to be similar to that of S. griseicolle but no information on egg-laying exists for this species either. Both black ies probably scatter the eggs broadcast on the water surface to hatch, after sinking, in the river bottom sediments (a habit known in many simuliid species).

Adult habits. Enormous populations of females can occur in the inhabited areas along the Euphrates, where S. buxtoni reaches minor pest status because of the irritation it causes to humans living in the villages or working in the orchards and farms located in the narrow strips of cultivated land (about 100–200 m wide) that stretch along the river banks. Abul-hab (1983) has described his experience as follows: ‘During July, 1977, the black y was on the wing between sunrise and sunset. It was ying in great numbers to the extent that it was diYcult in Al-Anbar Province for the writer to stay out-of-doors, on the river banks, for a long period. The local inhabitants stated that this situation lasted all summer’. Early morning, around 7.00 a.m., is usually the time of maximum ight activity. When attracted to humans the ies hover around the head, face, hands and legs scarcely ever taking a bloodmeal, but on donkeys and cattle they feed in huge numbers, engorging from the face, ears, chest, shoulders and belly of the animals. The ies have been seen hovering over sheep and goats ( Abul-hab and Shihab, 1980) and presumably also take blood from these domestic animals. There are no reports of ornithophily, but females possess the large claw-tooth characteristics of bird-biting species and it is likely that ies feed indiscriminately on domestic and wild birds, just as do the females of S. griseicolle which bite turkeys, pigeons, parrots and song birds in addition to livestock and (sometimes) humans. Females of S. buxtoni have not been examined for the possibility of larial parasite transmission but this line of research could be worth pursuing in Iraq; S. griseicolle has been known to harbour larial worms in Nigeria ( Crosskey and Crosskey, 1958).

Nothing is known of the behaviour of male ies. Only one specimen was ever found by Abul-hab, collected on 4 July 1977 at Anah (34ss29¾/41ss57¾). Otherwise the only collected males are those listed above from Baghdad, taken at lights in the city (presumably having emerged from the nearby river Tigris ) .