A remarkable teratological female of Megascolia (Regiscolia) maculata flavifrons (Fabricius, 1775) (Scoliidae: Scoliinae: Scoliini) with a supernumerary median ocellus is described and illustrated. While supernumerary ocelli have been reported before from Diptera, Orthoptera, and Hymenoptera, this is the first record of such a malformation from a scoliid wasp. Four other teratological scoliid wasps have been reported in the literature but all were gynandromorphs. A brief summary of known records of supernumerary ocelli among insects is provided.

Median ocellus, twin ocellus, binary anterior ocelli, para-median ocelli, teratology, aberration, malformation, morphology

According to Nichols (1989) teratology is the “study of structural abnormalities, especially monstrosities and malformations.” Most accounts of teratology in the literature derive from experimental manipulation of the developmental process, while naturally occurring malformations are less frequently reported. In the past, many of these malformations were often neglected or mentioned merely as footnotes. This is perhaps not surprising as most authors surely must have thought that no significant conclusions could be drawn from isolated aberrant individuals. Indeed, it is challenging to infer much from isolated cases (e.g., Glasgow 1925), but when teratologies are made known and eventually summed up with others, there exists a great potential for patterns to emerge and broader conclusions to be drawn. The description of individual cases serves to build up a larger data set from which explanatory hypotheses can be formulated, highlighting the great value of descriptive science (e.g., Grimaldi and Engel 2007). A great example is the occurrence of gynandromorphs among aculeates, where the gradual accumulation of often-isolated, published accounts over the last 125 years has amassed into a body of data sufficient for the exploration of generalized patterns (e.g., Wcislo et al. 2004, Michez et al. 2009, Hinojosa-Díaz et al. 2012), and has aided attempts to homologize traits across sexes (e.g., Michener 1944, Engel 2007). It is therefore worthwhile to contribute to the accumulation of data on teratologies in the hopes that someday sufficient numbers will exist to permit more critical study.

There exists a relative abundance of reports concerning insects with partially fused antennomeres (e.g., Asiain and Márquez 2009, Popovici et al. 2014), or gynandromorphs (e.g., Hinojosa-Díaz et al. 2012), particularly as these relate to understanding more standard morphologies, such as whether a reduction in total antennomere count results from fusion or loss. Less often are other structural anomalies reported, such as supernumerary appendages or organs like legs (e.g., Cockayne 1937), antennae (e.g., Cockayne 1938), ocelli (e.g., Engel et al. 2014), or even compound eyes (e.g., Banerjee and Kevan 1959).

The first major review of teratologies among Hymenoptera was by Dalla Torre and Friese (1899) who focused their attention on gynandromorphs. Balazuc (1958), however, was the first to provide a comprehensive account of teratological Hymenoptera, including all kinds of malformations. Among the aculeate Hymenoptera, malformed specimens are exceptionally well reported for bees (Anthophila), with gynandromorphs alone reported for more than 110 species in 29 genera (Hinojosa-Díaz et al. 2012). With respect to Scoliidae, however, the number of peculiar malformed specimens reported in the literature is limited to four records of gynandromorphs (De Romand 1835, Krombein 1949, Wolf 1989, Osten 1993). In the course of sorting several boxes of unidentified scoliid wasps VL recognized a female of Megascolia (Regiscolia) maculata flavifrons (Fabricius 1775) with four ocelli (Figs 1, 2). The aim of the present contribution is to describe and illustrate this specimen and to provide a short account on supernumerary ocelli in pterygote insects.

Figures 1–6. 

Megascolia (Regiscolia) maculata flavifrons (Fabricius). 1–4. Quadriocellar female from Mallorca. 1. Habitus in lateral view. 2. Habitus in dorsal view. 3. Head in dorsal view. 4. Ocellar area. 5–6. Normal female from Ibiza. 5. Head in dorsal view. 6. Ocellar area. Photos: Matthias Haase.

Measurements were taken using a Keyence VHX 5000 Digital Microscope. The morphological terminology for the description of the specimen is adopted from Betrem (1971). The photographs were captured with a Nikon D800 digital camera with a Nikon AF-S Micro-NIKKOR 60 mm 1:2,8G ED lens in combination with the software programs Helicon Remote, Adobe Lightroom und Helicon Focus Pro. The identification of the specimen, which is deposited in the entomological collection of the Übersee-Museum Bremen (UMB), is based on the key provided by Osten (2000).

Among the recorded wild forms of pterygote insects with supernumerary ocelli, two different kinds of teratology are known – those resulting from duplication of the anterior ocellus, such as reported here, or of the lateral ocelli (Table 1). Whereas most records report a supernumerary anterior ocellus, Engel et al. (2014) reported an augochlorine bee with five ocelli – a single median ocellus and two sets of posterior paired ocelli. The only other account of malformed posterior ocelli is that of Ashmead (1880) who described a new species of the aphelinid genus Aphytis Howard with the type specimens having “three ocelli triangularly arranged, with two smaller red ones back of these”. However, according to Rosen and DeBach (1979), “Ashmead apparently mistook the pigment spots, commonly seen in dry or slide-mounted specimens of small Chalcidoidea, for supernumerary ocelli.” While their assessment is likely accurate, it remains unclear whether Ashmead might have found a true malformation given that his type material for the species in question has been lost (Rosen and DeBach 1979; and sources cited therein). These two records aside, all other accounts pertain to modifications of the anterior ocellus and result either from an apparent division of the structure or for its reappearance.

Supernumerary ocelli have been reported from Diptera, Orthoptera, and Hymenoptera (Table 1), but since these particular deformations are not as abundant as gynandromorphs a proper name has never been established for them. Thus they appear under quite different ‘labels’ in the literature. It was perhaps the naturalist explorer Henry Walter Bates (1825–1892) who first recorded an observation of supernumerary ocelli, which he dubbed a “twin ocellus” (Bates 1863; the same term was used later by Brent 1886). Other authors described this unusual development as either “supernumerary median ocelli” (Blackman 1912), “four [dorsal] ocelli” (Smulyan 1923, Glasgow 1925, Hori et al. 1967), “para-median ocelli” (Glasgow 1925), “binary anterior ocelli” (Wheeler 1936, Weber 1947), “two median ocelli” (Blackman 1912, Slifer 1960, King and Slifer 1965, Hori et al. 1967), or “abnormal median ocelli” (King and Slifer 1965). The term ‘supernumerary ocelli’ seems appropriate for the general class of teratologies involving the duplication of ocelli, with individual malformations dubbed by the number involved (e.g., quadriocellar, quintocellar). Once a more sizeable number of these deformations are documented a more systematic classification can be established.

A casual perusal of the list of occurrences of supernumerary ocelli (Table 1) would give the impression that some groups are more prone than others toward developing such teratologies. All records of ants with supernumerary ocelli are from the subfamily Myrmicinae, and particularly the leaf-cutting ants (Attini), whereas all recorded Orthoptera are from a single genus (Melanoplus Stål). While on the surface this is interesting, it perhaps reflects more the interest of those working on such groups. For example, species of Melanoplus are some of the most intensely studied of agricultural pests, and Weber was particularly interested in attines during the course of his myrmecological career, perhaps accounting for the fact that all of his records stem from that one tribe (Weber 1947). Indeed, even Wheeler’s records stemmed largely from taxonomic work he was undertaking on the genus Atta Fabricius (Wheeler 1936, p. 188). Until more extensive studies into the occurrence of such teratologies are completed, it is impossible to say whether particular clades are more susceptible or not. In order to get an idea of the relative abundance of such malformed specimens we contacted several colleagues and asked for similar observations in their respective groups of Hymenoptera: Stephan Blank, Symphyta; Andrew Polaszek, Platygastroidea and Chalcidoidea; Heinrich Wolf, general Aculeata; Celso O. Azevedo, Bethylidae; Denis J. Brothers, Mutillidae, Bradynobaenidae, Plumariidae, and Scolebythidae; James M. Carpenter, Vespidae; James P. Pitts, Mutillidae and Pompilidae; Lynn S. Kimsey, Tiphiidae, Chrysididae, and apoid wasps; Michael Ohl, apoid wasps; Fritz Gusenleitner, Andrenidae. Since none had come across a similar malformation, we assume that the low number of published records generally reflects the rarity of this kind of teratology in Hymenoptera.

The presence of supernumerary ocelli is almost certainly not the result of mutation, and therefore not present in the genetic makeup of the individual or heritable, instead resulting from errors in the developmental process and formation of adult tissues. That said, for at least one report in Melanoplus, King and Slifer (1965) found that their quadriocellar individuals successfully reproduced and that a “large proportion” of the offspring were similarly quadriocellar in condition. This suggests that for some cases there might be a genetic component, although the general rarity of supernumerary ocelli in other groups tends to suggest that such apparent heritability is far from the norm. What is remarkable is that these aberrant individuals are often captured while carrying on otherwise seemingly normal lives, a particularly remarkable fact given that ocelli are implicated in light responses and orientation (e.g., Taylor 1981a, 1981b, Schuppe and Hengstenberg 1993, Warrant 2006, Berry et al. 2006, Viollet and Zeil 2013). The scoliid wasp reported herein was perfectly developed in all other respects, and it does not seem that it had to deal with negative effects caused by the supernumerary ocellus. The consequences of malformations such as this are hardly predictable given that a complete understanding of ocellar function remains elusive (e.g., Wilson 1978, Goodman 1981, Stange et al. 2002).

Investigating the supernumerary median ocelli one is tempted to interpret such a malformation as an individual evolutionary throwback considering the hypothesis on the evolution of the median ocellus in insects. Snodgrass (1935) surmised that the median ocellus was formed by the fusion of two primitive anterior ocelli, and according to Paulus (1979) the anterior ocellus is homologous to the anterior pair of Nauplius eyes in Crustacea and the pair of median ocelli in Limulus. Indeed, the fusion hypothesis of Snodgrass has considerable support (Mizunami 1994), and in various groups the paired origin remains visible during ontogeny (e.g., Patten 1887, Viallanes 1887, Mobbs 1979). Even in adults the median ocellus retains its paired innervation, while the lateral ocelli are singly innervated (e.g., Leydig 1864, Hesse 1901, Imms 1948). It seems plausible that due to some unknown disruption during development the fusion has failed in those individuals with two anterior ocelli. However, it is quite obvious that significantly more information is needed, including extensive documentation of further occurrences of supernumerary ocelli. It is hoped that this account will spur entomologists to pay greater attention to the occurrence of such teratologies and to put them on record. The scarcity of literature reports of aberrant insect specimens assuredly does not reflect their immense diversity nor their abundance in natural history collections.

We sincerely thank Detlef Pawelek (Bremen) for donating the scoliid wasp to the UMB, Laura C.V. Breitkreuz (Lawrence), Stefanie Krause (Berlin), Stephan Blank (Müncheberg), Tony Irwin (Norfolk), Andrew Polaszek (London), and Joachim Ziegler (Berlin) for providing us with literature, and Matthias Haase (Bremen) for providing the photographs. Ralf Höfel (Keyence International) kindly allowed use of the Keyence VHX 5000 during a two-day microscope demonstration. Finally, we would like to thank the two reviewers, Lynn S. Kimsey and Denis J. Brothers, for their valuable comments on the manuscript. This is a contribution of the Division of Entomology, University of Kansas Natural History Museum.