The Gulf of Guinea islands are here regarded as Príncipe, São Tomé and Annobón. Bioko is excluded because of its proximity to mainland Africa, with which it was connected in the past. Brooks & Jackson (2001) summarise the current knowledge of the Odonata of the latter island. There are no endemics among the 48 recorded species, all being shared with the nearby Cameroon mainland. The oldest records from the Gulf of Guinea islands are provided by Martin (1908) and Campion (1923). Longfield (1936) described the first and so far only endemic for the islands, Trithemis nigra. The type locality of the latter is Ogui Pipi on Príncipe, the collection dates are 7 December 1932 and 1 January 1933. The only odonatologist ever to visit the islands was Elliot Pinhey, who was on São Tomé in April and May 1971, but his visit yielded no surprises except for some sight records of a possibly endemic species. Pinhey (1974) reviews what is known about the dragonflies of the islands, but overlooked Compte Sart (1962), who dealt with some material from Annobón.

Table 1 lists all species known from the islands. A total of nineteen species is known, seven each from Príncipe and Annobón and fourteen from São Tomé. Orthetrum brachiale and O. stemmale have been confused in the past and possibly both species are present. Only the Príncipe record was specified as being the subspecies kalai of brachiale, which is now considered a synonym of stemmale. Most listed species are abundant and widespread throughout tropical Africa, many even reaching the even more distant Mascarenes. The Gulf of Guinea list should easily be extended with more of such species. Agriocnemis exilis, Enallagma glaucum, Orthetrum icteromelas, Rhyothemis semihyalina, Sympetrum fonscolombii, Trithemis annulata and Zygonyx torrida have for instance reached the Mascarenes, but none of the Gulf of Guinea islands.

Three of the listed species are of more interest. The endemic Trithemis nigra of Príncipe is only known from the two types collected in the 1930s. Pinhey (1974) saw a species of Gynacantha (or the closely similar genus Heliaeschna) on São Tomé on four occasions, but these eluded capture. He remarks that “forest species of these genera on an isolated island might be expected to be distinctive”. The Seychelles and the Mascarene archipelagos for instance each have an endemic Gynacantha. A single female Zygonyx has been collected from Annobón. Species of this genus favour water with a strong current. Pinhey (1974) remarks that he did not see “any Zygonyx near any of the waterfalls and swift-flowing streams” on São Tomé. The well-dispersing Zygonyx torridus has colonised Mauritius, while the Seychelles, Comoros and Madagascar all have endemic species of Zygonyx. Pinhey (1975) examined the Annobón female briefly, stating that “it appears to be flavicosta”. This is an equatorial forest species, which is quite widespread in West and Central Africa. Nonetheless a record from this distant island seems rather surprising and perhaps an endemic species is concerned.

Table 2 compares the Gulf of Guinea Islands with the other volcanic islands of tropical Africa. The best comparison can be made with Mauritius and Réunion. These are larger, but also more distant, than the Gulf of Guinea Islands, but have similar ecological conditions and are relatively well studied. Their dragonfly faunas are much richer in species numbers and endemics. In addition the Mascarenes harbour two endemic genera, Coenagriocnemis and Thalassothemis. When we compare the dragonfly and vertebrate faunas (with land birds as an example in table 2) of the Gulf of Guinea and Mascarene islands, it seems that the dragonfly fauna of the former is disproportionately poor, considering sufficient suitable habitat is present. Pinhey (1974) states that “compared to other orders, particularly Lepidoptera, rich in species or subspecies only known from this islands, the few endemics are remarkable for their paucity”. He suggests that “the prevalence of widespread species in restricted territories may inhibit further competition”. This explanation is unsatisfactory because the Mascarenes harbour a similar set of widespread species, as well as a fair number of endemics. Another reason for the paucity could be an ecological disaster in the past, but the first hypothesis to falsify is that of under-sampling. The number of records from Príncipe and Annobón is negligible, and neither has ever been visited by a specialised collector. Elliot Pinhey only visited the northern and eastern parts of São Tomé, which is the more cultivated part of the island. Furthermore his collecting may have been inhibited by the climate that he found “almost unbearable in April to scramble up the mountain after about 9 a.m.” On the whole, it seems possible that the islands have yet to yield endemic species, or even genera, of dragonflies.

Table 1. Odonata recorded from the Gulf of Guinea Islands

Reported by: C: Campion 1923, L: Longfield 1936, M: Martin 1908, P: Pinhey 1974, S: Compte Sart 1962. Whether a species is also known from Mauritius and/or Réunion is also shown.

	Príncipe	São Tomé	Annobón	Mascarenes
Zygoptera Coenagrionidae
Ceriagrion glabrum	M	C P		+
Ischnura senegalensis			M S	+
Anisoptera Ashnidae
Anax ephippiger		P		+
Anax imperator		P	M S	+
Gynacantha sp.		P
Libellulidae
Crocothemis erythraea		L P
Crocothemis sanguinolenta		P
Diplacodes lefebvrei		C P		+
Orthetrum africanum	L	P
Orthetrum brachiale / stemmale	P	L P	P S	+
Orthetrum julia	L P	C L P
Palpopleura lucia	L P	C L M P	M
Pantala flavescens	M	C P		+
Tholymis tillarga		P		+
Tramea basilaris		P	M	+
Tramea limbata			S	+
Trithemis nigra	L
Zygonyx sp.			L

Table 2. Comparison of the volcanic islands of tropical Africa and their dragonfly faunas

The islands are sorted according to their distance from a larger land mass (i.e. Africa or Madagascar).

	area (km²)	maximum altitude (m)	distance to land mass (km)	endemic land bird species	dragonfly species	endemic dragonfly species
Bioko	2,017	3,011	34	2	48	0
Príncipe	139	948	210	7	7	1
São Tomé	857	2,024	255	16	14	0
Comoros*	2,023	2,361	300	19	22	7
Annobón	21	613	340	2	7	0
Réunion	2,512	3,069	600	4	18	1
Mauritius	1,865	824	840	7	25	6
Rodrigues	109	393	1,470	2	2	1
Ascension	97	859	1,504	0	0	0
St Helena	122	823	1,913	1	2	1

* consists of four larger islands

References

Brooks, S.J., & K.A. Jackson, 2001. The Odonata of Bioko, Republic of Equatorial Guinea, with the description of fan-shaped setae on early instar Libellulidae larvae. Odonatologica 30(1): 29-38.

Campion, H., 1923. Notes on dragonflies from from the Old World islands of San Tomé, Rodriguez, Cocos-Keeling and Loo Choo. Ann. Mag. nat. Hist. (9) 11: 22-27.

Compte Sart, A., 1962. Resultados de la expedición Peris-Alvarez a la isla de Annobón. 11. Odonata. Bol. R. Soc. Esp. Hist. Nat. (B) 60: 35-54.

Longfield, C., 1936. Studies on African Odonata, with synonymy, and descriptions of new species and subspecies. Trans. R. ent. Soc. London 85(20): 467-498.

Martin, R., 1908. Voyage de Leonarda Fea dans l’Afrique Occidentale, Odonates. Annali Mus. civ. Stor. Giacomo Doria, Genova 3(43): 649-667.

Pinhey, E., 1974. Odonata of the Northwest Cameroons and particularly of the islands stretching southwards from the Guinea Gulf. Bonn. zool. Beitr. 25(1-3): 179-212.

Pinhey, E., 1975. A collection of Odonata from Angola. Arnoldia 7(23): 1-16.

Table 1. Odonata recorded from the Gulf of Guinea Islands

Zygoptera

Coenagrionidae

Ceriagrion glabrum

Table 2. Comparison of the volcanic islands of tropical Africa and their dragonfly faunas

References