Revalidation of the polymorphic genus Acephalonomia (Hymenoptera: Bethylidae) and description of a new species from Micronesia

The genus Acephalonomia Strejček, 1990 is revalidated and its single species, Acephalonomia cisidophaga Strejček, 1990, from Czech Republic and Slovakia is restituted in the original combination. The revalidation is based on distinct characters: antennae with eight fl agellomeres and prestigmal abscissa of R1 vein dilated. The intraspecifi c polymorphism is also relevant for revalidation, although not exclusively so. We redescribe and illustrate the type species Acephalonomia cisidophaga and describe and illustrate a second new species with eight antennal fl agellomeres from the Mariana Islands, Acephalonomia micronesica sp. n., and provide a key to this genus. ZooBank Article Registration: http://zoobank.org/urn:lsid:zoobank.org:pub:900C0CE0-650A-4321-B90C-02FDFB2EE9B0


INTRODUCTION
The monotypic genus Acephalonomia was described by Strejček (1990) to accommodate a new species, Acephalonomia cisidophaga Strejček, 1990, having only 8 fl agellomeres. So far only the type species has been known with such antennae. The author stated that Acephalonomia is similar to Cephalonomia Westwood, especially C. formiciformis Westwood, but he did not explain the nature of that similarity; at the same time he did affi rm that the body plan of both genera is very different.
De Rond (2001) commented that the male genitalia, the wing pattern and the general body plan of Acephalonomia did not justify a genus separate from Cephalonomia. Thus, he proposed Acephalonomia as a junior synonym of Cephalonomia.
While examining the collection of the Bernice Pauahi Bishop Museum (Honolulu, U.S.A.) we discovered a species of bethylid that perfectly matched the concept of Acephalonomia proposed by Strejček (1990) with eight antennal fl agellomeres, wing polymorphism and the same hosts, Ciidae beetles inhabiting polypore fungus.
Thus, the main goal of this contribution is to revalidate Acephalonomia, and the description of the second species of Acephalonomia. We also take the opportunity to summarize the available information on the biology and taxonomy of Acephalonomia cisidophaga and amend the generic diagnosis by including additional characters.  (Figs 1-3). Body 1.3 mm long. Colour. Body castaneous, except mandibles, tibiae yellowish, tarsi and setae dark brown, wings hyaline, veins castaneous. Head subrectangular in dorsal profi le, weakly coriaceous. Mandible apparently with three large distal teeth, lowermost largest. Antennal scape distinctly elongated, as long as fl agellomere VIII; fl agellomeres I-II distinctly shorter than others. Ocelli present. Dorsal pronotal area bell-shaped, progressively widening posteriorly. Mesoscutum transverse, 2 × as long as wide and as long as mesoscutellum; notaulus absent; parapsidal signum subparallel. Mesoscutellum progressively narrowing posteriorly, anterior margin straight and posterior margin outcurved. Mesoscutum-mesoscutellar suture sulcate, foveae distinct. Metapectal-propodeal disc longer than dorsal pronotal area, transverse anterior, transverse posterior, metapostnotal median carinae absent, lateral carina incomplete. Mesotibia not spinose. Metasoma elongated, slightly fl attened, polished; petiole very short; metasomal tergum II longer than others, posterior margin with short setae.
Macropterous male. Body 1.2 mm long. Head as long as wide, subpentagonal in dorsal profi le, with side outcurved, weakly coriaceous. Mandible apparently with three large distal teeth, lowermost largest. Antennal scape distinctly elongated, longer than fl agellomere VIII; fl agellomeres I-II shorter than the others. Dorsal pronotal area The images were taken under a Leica Z16 APO stereomicroscope coupled to a Leica DFC 2 video camera and using the Modular Dome Illumination System of Kawada & Buffi ngton (2016). Helicon Focus was used to combine the images.
The data in the section on the specimens examined is literally transcribed from the labels, additional data are in square brackets.
Distribution. Western Palaearctic Region (known from Czech Republic and Slovakia) and Oceanian Region (Northern Mariana Islands).
Micropterous male. Body 1.0 mm long. Head subrectangular in dorsal profi le, rounded corners, weakly coria-ceous. Mandible apparently with two large distal teeth, lowermost largest. Antennal scape distinctly elongated, as long as fl agellomere VIII; fl agellomeres I-II shorter than the others. Dorsal pronotal area rectangular, similar width along its length. Mesoscutum transverse, 2 × as long as wide; notaulus and parapsidal signum absent. Mesoscutellum wider medially and progressively narrowing both anteriorly and posteriorly. Metapectal-propodeal disc as long as dorsal pronotal area, transverse anterior, transverse posterior, lateral, metapostnotal median carinae absent, not punctate. Mesotibia not spinose.  Remarks. The description of this species was based on a large series of micropterous and macropterous specimens of both males and females from polypore fungi collected in the Czech Republic and Slovakia. The holotype was collected from burrows of a ciid beetle, Rhopalodontus Mellié, in Trametes sp. on Fagus sylvatica (Strejček 1990). The sexual dimorphism of micropterous specimens is minimal. In the macropterous forms the only prominent difference between the sexes is the shape of head in dorsal profi le: subpentagonal in males and subrectangular in females. Interestingly, macropterous females are more similar to micropterous males and females than to macropterous males.
Distribution. Czech Republic and Slovakia.

Distribution. Known only from the type locality.
Remarks. The specimens of this species emerged from beetles of the family Ciidae living in polypore fungus. A total of 27 micropterous and one macropterous female were reared. Although this is a case of evident polymorphism, the difference between them is minimal, restricted to expected characters such as absence of ocelli and reduction of mesoscutum and mesoscutellum. There are only minute difference in measurements of the micropterous specimens.
A. cisidophaga and A. micronesica have some morphological similarities, such as antennae with eight fl agellomeres; polymorphism with macropterous and micropterous forms; notaulus absent; parapsidal signum present only in macropterous form; forewing of macropterous form with Radial (R) cell closed, C and 2r-rs&Rs veins absent, Rs&M vein and prestigmal abscissa of R1 vein dilated and pterostigma wide and semicircular; metapectal-propodeal disc without anterior, posterior and median carinae.
However, the micropterous form of A. cisidophaga has ocelli, wings that surpass the posterior margin of mesoscutellum; and fl agellomere I of the macropterous form is as long as fl agellomere II, metapectal-propodeal complex punctate and lateral carina incomplete; whereas the micropterous form of A. micronesica does not have ocelli and the wings surpass posterior margin of mesoscutellum; and fl agellomere I of the macropterous form is shorter than fl agellomere II, metapectal-propodeal disc polished and lateral carina complete.

DISCUSSION
Flat wasps evolved to exploit small larvae occurring in cryptic situations like soil, stems, wood or seeds (Evans, 1964). The host preference of bethylids is exceptionally uniform. Bethylinae, and a few Epyrinae, attack larvae of Lepidoptera, while the other subfamilies attack larvae of Coleoptera. However, the host range of Bethylidae is poorly known .
Wing polymorphism is recorded for several Scleroderminae. Cephalonomia perpusilla Evans has an unusually complex polymorphism (Evans, 1963). Yang et al. (2012) suggest that a long photoperiod and strong light promotes the development of winged females in Sclerodermus pupariae Yang & Yao. Acephalonomia may also be infl uenced by photoperiod as it is morphologically similar to the genus Sclerodermus. The cosmopolitan genus Sclerodermus is interspecifi cally variable with macropterous, micropterous and apterous forms, as well as intraspecifi cally variable (e.g. S. pupariae). However, there are only two species of Acephalonomia, both with micropterous and macropterous individuals, so polymorphism is probably a generic feature.
The forewing venation of Acephalonomia is also very characteristic in lacking a closed cell, C and 2r-rs&Rs veins, and with Rs&M vein and prestigmal abscissa of vein R dilated. In this respect this genus is similar to Megaprosternum. Nevertheless, in Megaprosternum the pterostigma is small and linear, whereas in Acephalonomia it is large and subcircular (Azevedo, 2006;Gupta et al., 2017).
Polymorphism and simple morphology are more evident in Scleroderminae than in other bethylids.
Cephalonomia and Acephalonomia have some morphological similarities, such as a tiny body; forewing without C, 2r-rs&Rs and A veins. However, Cephalonomia has antennae with 10 fl agellomeres; mesonotum with scutum and scutellum fused in micropterous and apterous forms; metapectal-propodeal complex margined on sides by carinae, occasionally with median carina; and apterous forms; whereas, Acephalonomia has antenna with eight fl agellomeres; mesonotum with scutum and scutellum not fused in micropterous form; metapectal-propodeal complex occasionally margined on sides by carinae; and lacks an apterous form. These characters led us to revalidate the genus.
This genus can be keyed by modifying the key of Azevedo et al. (2019)  The genus has an accentuated disjunct distribution with Acephalonomia cisidophaga in Europe (Czech Republic and Slovakia) and A. micronesica sp. n. on Tinian Island (Mariana Islands). This widely broadens the known distribution of the genus, and the geographical gap indicates that this genus may be more widely distributed. One particular reason for this gap could be few collectors. The specimens of Acephalonomia are tiny and are parasitoids of a tiny ciid beetle, which occur in polypore fungus, so they are collected using only by a very specifi c fi eld protocol. Future studies that focus on them will undoubtedly increase the number of species in this genus and possibly partially fi ll the geographical gap.