A new genus, Helenanomalon gen. n., of the ichneumonid subfamily Anomaloninae is described for two newly described species, Helenanomalon ashmolei sp. n. and H. bonapartei sp. n. Helenanomalon species are endemic to the remote South Atlantic island of St Helena, where they are the only known anomalonines. Unusually amongst anomalonines, there seems to be pronounced sexual dimorphism. The possible affinities of Helenanomalon are discussed.

Taxonomy, new genus, new species, south Atlantic, UK overseas territory

The remote, southern Atlantic island of St Helena (a UK overseas territory) has, unsurprisingly, a very small fauna of endemic Hymenoptera. Being 1,960 km from the nearest landmass (Africa), only a few Ichneumonoidea have colonised the island under their own steam, although a variety of tramp species have been inadvertently introduced. The invertebrate fauna of two key areas of St Helena was recently catalogued by Ashmole and Ashmole (2004) and Mendel et al. (2008), with the latter report based on extensive material collected in the Central Peaks area of the island in 2005–2006. Amongst the five species of Ichneumonidae collected in that survey were two male specimens of the subfamily Anomaloninae that could not be identified to genus. There are also two published mentions of an undescribed anomalonine genus from St Helena. A short note by Ian Gauld, in his revision of the genera of Anomaloninae (Gauld, 1976), on an undescribed genus from St Helena, led to the rediscovery of a further male specimen in the Natural History Museum (hereafter BMNH) collection. Anomaloninae specimens collected in the Eastern Arid Area of the island by the Belgian expeditions of 1965–1967 are mentioned in a report on the ichneumonoid fauna of St Helena by Decelle (1976) as having been identified as a new genus by Henry Townes. The two females are deposited in Musée de l’Afrique Centrale (Tervuren) (hereafter RMCA) and were labelled as a ‘new genus of Gravenhorstiini’ by Henry Townes in 1972. These five specimens seem to be the only specimens of Anomaloninae to have been collected on St Helena.

Assigning the St Helena anomalonines to a genus, or defining a new genus to accommodate them, has proved problematic. Gauld’s (1976) analysis of anomalonine relationships informed his redefinitions of the genera but was based on phenetic analysis of morphological characters. I had hoped to reanalyse Gauld’s data using cladistic methods, and to include the St Helena specimens, as a test of their generic status. However, Gauld did not include a character matrix in his paper, stating that the data had been deposited in the BMNH library. Unfortunately, there is no trace of any such documents in either the library or the archives of BMNH. Given the information provided by Gauld in his generic revision, it is impossible to reconstruct his character matrix so a new genus is proposed here on the basis of character combinations that seem to preclude its placement in any described genus, and some apomorphic characters that attest to its long evolutionary independence from other lineages. I.D. Gauld and H.K. Townes had, probably independently, concluded that the males seen by Gauld and the females seen by Townes represented an undescribed genus. The males and females of this new genus are dissimilar in numerous ways, necessitating the description of two separate species.

Specimens are deposited in the Natural History Museum, London (BMNH) and the Musée de l’Afrique Centrale (Tervuren) (RMCA). Originally, three males were deposited in BMNH and two females in RMCA. Through the kind cooperation of Eliane de Coninck, curator at RMCA, one of each sex were exchanged so that both institutes now hold both sexes and both species.

Morphological terminology follows Gauld (1991). The format of the generic description follows that of Gauld (1976), for ease of comparison with other anomalonine genera, including numerous indices that Gauld (1976) employed. Photographs were taken using a Canon EOS 450D digital camera attached to a Leica MZ12 stereomicroscope. Partially focused photographs were combined using Helicon Focus software.

Only six species of Ichneumonidae have been recorded from St Helena, namely Diadegma mollipla (Holmgren), Diplazon laetatorius (Fabricius), the endemic subspecies Echthromorpha agrestoria atrata Holmgren, the endemic species Netelia insulicola (Morley), and now Helenanomalon ashmolei sp. n. and H. bonapartei sp. n. (note that Yu et al. (2012) mistakenly list Diadegma semiclausum (Hellén) from St Helena, citing Wagener et al. (2006), who actually only record D. mollipla from the island). It seems surprising that there is an endemic genus on this island, given that two of the other ichneumonids (Diadegma mollipla and Diplazon laetatorius) are widespread, probably introduced, associates of agriculture and the other two are closely related to extralimital species (Netelia insulicola to African species and E. agrestoria atrata is currently classified as a subspecies of the wide-ranging, polytypic E. agrestoria (Swederus)). However, the Central Peaks and Prosperous Bay areas of St Helena are home to other endemic genera of insects and these are clearly areas of special habitat that have allowed the evolution of distinct lineages in great isolation. It should also be noted that the anomalonine fauna of Africa is poorly known, with few species described; the St Helenan insect fauna shows most affinity with the African fauna (Mendel et al. 2008) and the closest relatives of Helenanomalon may well be found there.

With one species known only from females and the other only from males, there must remain some doubt as to whether these are really separate species. Given the small anomalonine fauna likely to be present on St Helena, one hypothesis is that these specimens represent the two sexes of the same species, displaying a more extreme sexual dimorphism than is otherwise known within Anomaloninae. In this scenario, females show striking adaptations for locating and accessing hosts, whilst males have rather more generalised morphology. Development in different sizes of hosts will, of course, produce different sizes of adult ichneumonids, even in koinobiont endoparasitoids such as anomalonines, and the two females collected so far, much smaller than the males, may simply have developed in rather smaller hosts than the males that have been collected; anomalonines are rarely host-specific, usually accepting hosts across rather taxonomically wide host ranges within particular parasitoid searching niches (e.g., Shaw et al. 2009). However, I favour the alternative hypothesis, that these are separate species. In favour of this are the differences in wing venation; the well-developed notauli in the male but not the female; the larger size of the males, when often it is the females that are larger in ichneumonids; and the fact that the two sexes were collected in different areas of the island, in different habitats (the females in the more arid Prosperous Bay, the males in the wetter Central Peaks area). The sexes do share numerous characters and I am convinced that they are congeneric. The fauna of St Helena has now been better surveyed than that of many remote islands, nevertheless, further collecting should produce more specimens of this genus on St Helena and confirm or refute the taxonomy proposed here. Fresh material would obviously be very useful for DNA sequencing.

An investigation of the evolutionary relationships of Helenanomalon would be rewarding in potentially shedding light on the origins of this geographically isolated genus. The classification of Anomaloninae as a whole would certainly repay a detailed phylogenetic study. In Gauld’s (1976) key to genera of Anomaloninae, males of Helenanomalon bonapartei will fail to travel properly from couplet nine, because the clypeus is truncate apically and the mesoscutum evenly rounded but the notauli are present and strong. Females, and males if the distal abscissa of hind wing vein Cu1 is regarded as missing (at couplet five), will reach couplet 40, where they will key to Habronyx (Camposcopus), but by ignoring the fact that the clypeus does not have a median tooth. Several characters preclude the classification of these specimens in Habronyx, such as the apically truncate clypeus, vestigial transverse carina of the mesosternum and the undivided male metasomal tergites 8+9. The aedeagus most closely resembles that of Habronyx (Habronyx) australasiae (Morley), as illustrated by Gauld (1976). The main difficulty faced in trying to place this taxon in Gauld’s scheme of relationships is that Gauld’s (1976) proposed set of relationships is based on percentage similarity (this work preceded the widespread acceptance of cladistic methods in phylogeny reconstruction) and not on character distributions. In the absence of clades defined by apomorphies we can only suggest that Helenanomalon seems to be related to Trichomma or Habronyx. The former hypothesis is based on overall similarity, including, in some species of Trichomma, the lack of a clypeal tooth and the distal abscissa of hind wing vein Cu1. Helenanomalon differs most obviously in the short setae on the eye and shorter ovipositor than in Trichomma. The strong notauli (in the male only though) and various trends, including the short epicnemial caria and short, sparse setae on the surface of the eye, are present in a few species of Habronyxs.l.

In several features, such as lack of a clypeal tooth and the form of the epicnemial carina, Helenanomalon resembles Habronyx (Austranomalon) but differs in the truncate, simple clypeus (when truncate in Austranomalon then a clypeal tooth is present); the aedeagus has a well-developed, apical, crest-like area; and possible sexual dimorphism in tarsal claws, which is the opposite to the condition found in Austranomalon, i.e. the male claws in Helenanomalon are strongly curved and pectinate, those of the known females weakly curved and scarcely pectinate. Females of Helenanomalon have strikingly short antennae, very unusual for an anomalonine, although this autapomorphy does not help place the genus. There are only small differences between some of the genera of Anomaloninae whilst a few genera as currently defined seem to encompass more variation between species classified in the same genus than is found between other genera. Habronyx is a good example of the latter, polythetic genus.

The most distinctive feature of Helenanomalon, that should render females instantly recognisable, is the short, clavate antennal flagellum of the female (but it is not known if this is true for the unknown female of H. bonapartei sp. n.). Males are less easily recognised but have a unique combination of characters, including the apically truncate clypeus, lacking a tooth; the strongly curved, completely pectinate tarsal claws; short, sparse setae on the eye surface; and the incomplete posterior transverse carina of the mesosternum. Females lack notauli and have only basally pectinate claws. Another potential characteristic of the genus is pronounced sexual dimorphism.

Thank you to Howard Mendel and Philip and Myrtle Ashmole for collecting a wealth of insect specimens from St Helena, which prompted me to describe this genus. I am grateful to Eliane de Coninck and Stéphane Hanot for the loan of specimens from Tervuren and for agreeing to the exchange of a female and male between institutes. Harry Taylor at BMNH took the lovely photograph of the holotype male of H. bonapartei. I am grateful to Heinz Schnee and Seraina Klopfstein for their helpful reviews of the manuscript, particularly their opinions on the number of species represented by these few specimens.