Simulium (Pomeroyellum) alcocki Pomeroy, 1922

Mustapha, M., Jarvis, W. & Post, R. J., 2004, The Simuliidae (Diptera) of the Republic of São Tomé and Príncipe, including the description of a new species, African Invertebrates 45, pp. 143-156 : 149-152

Simulium (Pomeroyellum) alcocki Pomeroy, 1922

( Figs 12–20 ) Simulium alcocki Pomeroy, 1922 (original description [ Nigeria], ơ, ^, pupa); Gibbins 1941 ( S. alcocki variety henrardi ); Roubaud & Grenier 1943 (larva); Freeman & de Meillon 1953 (ơ, ^, pupa);

Crosskey 1960 a (larva); Garms & Post 1967 (larval branched hairs, ơ ventral plate); Crosskey &

Howard 1997 (country distribution); dos Santos Grácio 1999 (first record São Tomé).

New material seen:

SÃO TOMÉ ISLAND: 22 larvae, 15 pupae, site 6, 12, xi.1998, RJP ( BMNH) ; 70 larvae, 50 pupae, site 6, 12, xi.1998, RJP (ST&P); 1 ơ (pinned), 1 ơ (slide), 1 ^ (pinned), 3 ^ (slides), 11 larvae, 21 pupae, site 7, 12, xi.1998, RJP ( BMNH); 3 ơ (pinned), 2 ^ (pinned) , 38 larvae, 36 pupae, site 7, 12, xi.1998, RJP (ST&P); 27 larvae, site 8, 12.xi.1998, RJP (ST&P); 1 pupa, site 9, 11.xi.1998, RJP (ST&P).

Material seen from Natural History Museum ( BMNH):

Paratypes: NIGERIA: reared adults 2ơ2^, BM 1921­ 148 , Ibadan , 06.xii.1920, A. W. J. Pomeroy . Other material: CENTRAL AFRICAN REPUBLIC: 5 pupae, 2 larvae, Bangui, xii.1984 – vi.1985, S. E. O. Meredith . DEMOCRATIC REPUBLIC OF CONGO:

4^, BM 1951­ 347 , Blukwa, 1951, A. Fain; slide of 8 filament pupal gills labelled S. alcocki variety henrardi ; slide of 8 filament pupal gill labelled S. alcocki variety henrardi, Leo II Rhodiby , 6.xii.1934, C. Henrard. EQUATORIAL GUINEA: 2 pupae, Rio Sampaca, 8.iv.1998, P. J. McCall; 2 pupae, Rio Biolo / Timbabe, 8.iv.1998, P. J. McCall. GHANA: 1 pupa , BM 1949­ 525 , M. H. Hughes; reared adults 2ơ2^, BM 1950­ 632 , Yahala, small stream near Jo, 07.x.1950, L. Berner; 1ơ, Senchi, vi.1955, M. Hughes. GUINEA: 6 pupae, 5 larvae, Saba. b. Santia , 8.iii.1963 , R. Garms. NIGERIA: 10 pupae, 5 larvae, Abuja , 1959 , R. W. Crosskey; 16 larvae, Abuja , 1959 , R. W. Crosskey; 2 pupae, Vogu peak, 4500 ft, Northern Nigeria, 17.v.1969, H. Roberts. MALAWI: 1 pupa, Limbe , 14.viii.1952, L. Berner; 11 pupae , BM 1952­ 451 , 11.viii.1952, L. Berner; 2 reared ^, numbered 1738, Thyolo , R. C. Woods. RWANDABURUNDI (formerly Ruanda­Urundi): 1 reared 8 filament ơ , BM 1951­ 347 , 1951 , A. Fain. SIERRA LEONE: 3 pupae, 1926, B. Blacklock ; 2ơ, 2^, BM 1925­ 564 , xi.1925, B. Blacklock. SUDAN: 4 pupae, Khor Bangara, 5.x.1949, D. J. Lewis. TANZANIA: 1 pupa, Mahenge Mountains, 11.viii.1952, L. Berner. UGANDA: 2 pupae, 2 larvae, West Nile District , 20–21.x.1964 , R. W. Crosskey .

Material seen from the Instituto de Higiene e Medicina Tropical ( IHMT) (for full explanation of river sites and bioecological data see Santos Grácio 1999):

SÃO TOMÉ ISLAND: 1 larva on slide, no 545 , 2 pupae on slides, no 215 & 216, site 23, 28, vii.1988, AJSG ; 1 pupa on slide, no 207, site 28, 08.viii.1988, AJSG ; 3 pupae on slides, no 89, 90 & 91, site 30, 30.vii.1988, AJSG .

Material seen from the Koninklijk Museum voor Midden­Afrika ( MRAC): DEMOCRATIC REPUBLIC OF CONGO: 1 pupa on slide, River Mampeza, Leopoldville; 5.xi.1942, Dr Henrard; 1 pupal skin on slide, labelled S. alcocki variety II, River Binga; 2 reared adult males, labelled Paratypes of S.alcocki variety henrardi, Leopoldville , no 208, 19.viii.1941, Dr Henrard; 1 reared adult female labelled ‘Eg3 A’ type II, River du Hazaret, Leopoldville, no 105, 19.iv.1941, Dr Henrard; 1 reared adult female, River du Hazaret, Leopoldville, no 105, 19.iv.1941, Dr Henrard.

Remarks: Simulium alcocki was not found in collections from Príncipe, but it made up approximately 30 % of samples from São Tomé, mostly in the northeast of the island. All life stages of S. alcocki examined were similar to descriptions in published records and museum material from East, Central and West Africa (including pupal gill variation).

The pupal gill branching pattern of S. alcocki collected from São Tomé island during the present survey was of two types. The first was the common seven filament type as recorded by Crosskey (1960 b) from Nigeria and the Mount Cameroon area, and by Grenier et al. (1960) from across West Africa. The second had eight filaments (as illustrated by Freeman & de Meillon (1953) from the Sudan ­ see their figure 9m) and reported by dos Santos Grácio (1999) from São Tomé . In most places where it was found on São Tomé the seven filament form was sympatric with the eight filament form. A few specimens had a ‘vestigial’ eighth filament, and some others had seven filaments on one side and eight on the other. Examination of the external morphology of larvae, pupae and adults, and genital preparations from pupae and adults revealed no other differences between the seven and eight filament forms. The extra filament is clearly an example of intraspecific variation. Grenier & Rageau (1949) have also described specimens with seven filaments on one side and eight on the other within populations from Cameroon .

The possession of eight gill filaments is the sole defining character mentioned by Gibbins (1941) in his description of S. alcocki variety henrardi . The holotype pupa of Simulium alcocki variety henrardi , described by Gibbins in 1941 from the Mampoza river at Leopoldville (now Kinshasa), could not be located. Gibbins (1941) also recorded larvae, pupae and adults of S. alcocki variety henrardi from two sites in Uganda, but this material was also not located during this study.

However, some material collected by Henrard was obtained from MRAC, including two pinned adult males labelled ‘paratype’ and determined as S. alcocki variety henrardi by Gibbins, two pinned adult females and two slides of pupal gills. The males were also labelled ‘8 filament’, but on one the label had been later changed to ‘7 filament’. One of the pinned adult females was labelled S. alcocki type II and the other did not have a species label on it, but was identified as S. alcocki . An eight filament reared male adult which Fain collected in Rwanda­Burundi is present in BMNH. All external morphological features of these adults were consistent with those of typical S. alcocki (from published descriptions and specimens examined in BMNH).

It was not possible to view the genitalia because these were already missing from the ‘8 filament’ male specimen labelled ‘paratype’ from MRAC. The first slide sent from MRAC was labelled as ‘ S. alcocki variety henrardi ’. The second slide was labelled ‘ S. alcocki variety II’. Two slides of pupal gills labelled S. alcocki variety henrardi were also present at BMNH. These slides were assumed to be Gibbin’s material because of his usual style of ringing his slide preparations with a black plastic material. The pupal gills on all these slides are identical to those of the eight filament S. alcocki present on São Tomé and different from the eight filament gill structure of Simulium santomi sp. n. described above.

Based on this evidence we have concluded that the seven filament and eight filament forms of S. alcocki on São Tomé are variations of the same species, and that the eight filament form is that described by Gibbins (1941) as S. alcocki variety henrardi , which is itself an example of intraspecific variation in the pupal gill, and not a subspecies. The name henrardi should henceforth be considered a junior synonym of S. alcocki .

Figures

Figs 12­ 20. Simulium alcocki Pomeroy. 12. Pupal gill of variety henrardi. 13. Typical pupal gill. 14. Gonocoxite and gonostyle. 15. Pupal ventral onchotaxy. 16. Larval postgenal cleft. 17. Female hind leg. 18. Ventral plate and median sclerite. 19. Larval abdominal setae. 20. Paramere.