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84 entomologische berichten
80 (3) 2020
Vanhornia leileri, a new species and
new family for the Netherlands
(Hymenoptera: Vanhorniidae)
J.D.M. (Dick) Belgers
Wim Klein
Theo M.J. Peeters
KEYWORDS
Eucnemidae, dead wood, Proctotrupoidea, skylight
Entomologische Berichten 80 (3): 84-88
On the 26th of June 2019, in Wageningen (Province of Gelderland) two
female specimens of Vanhornia leileri were collected from two skylights,
situated in the roof of a covered walkway between a house and a shed.
Vanhornia leileri is the only European representative of the Vanhorniidae,
a family that has not been previously reported from the Netherlands.
Vanhornia leileri is a very rare parasitoid wasp of false click beetles
(Eucnemidae).
Introduction
In the period May-July 2019, the first author collected and
photographed a large number of crabronid wasps (Crabronidae)
from skylights behind a house in Wageningen (province of
Gelderland). The second author found among these collected
wasps two specimens of an unknown species, that the third
author recognized as Vanhornia leileri Hedqvist (figure 1). The
family Vanhorniidae, to which this species belongs, has not
been reported from the Netherlands up till now. This article
discusses the collecting method, taxonomy, distribution and
biology of this new and very interesting species.
Skylights
Two V. leileri specimens were collected from two skylights situ-
ated in the roof of a covered walkway between a house and a
shed (figure 2). The skylights (surface area approx. 1 m2 and
depth approx. 50 cm) have a similar effect on flying insects as
emergent traps. During the day, large numbers of flying insects
gather in the transparent domes of the skylights. They sit or fly
around in the concave underside of the domes where they can
easily be collected.
Over the past five years a number of fly (Diptera) and cicada
species (Cicadellidae) that were collected from these skylights
have been reported new to the Dutch fauna (Belgers 2019, Beuk
& Belgers 2017, De Bree et al. 2019, Den Bieman 2017, Den
Bieman & Van Klink 2015). In the vicinity of the skylights are
gardens with a few large maple and birch trees and a road with
on both sides a large number of old oak trees.
Taxonomy and distribution
Crawford (1909) described the new genus Vanhornia for which he
created the new family Vanhorniidae. Vanhorniidae is one of the
smaller families that belong to the superfamily Proctotrupoidea.
In the Netherlands, the Proctotrupidae (‘priemwespen’) and
Heloridae (‘gaasvliegwespen’) are also known from this super-
family. According to Townes & Townes (1981) Vanhorniidae is a
subfamily of Proctotrupidae with two genera: Heloriserphus and
Vanhornia. The genus Heloriserphus contains two species from
Chile (Townes & Townes 1981). Masner (in Townes & Townes
1981) does not agree with the classification of Townes & Townes
(1981), but considers Heloriserphus as a distinct subfamily that
should be placed at the base of the family Proctotrupidae. Here
we follow Masner’s vision.
Within the genus Vanhornia, three species have been de-
scribed: V. eucnemidarum Crawford, V. guizhouensis (He & Chu)
and V. leileri. Vanhornia eucnemidarum lives mainly in eastern
North America, from Quebec to Florida, but has recently also
been reported from the western part of North America (Manitoba)
and from South Korea (Choi & Lee 2012, Deyrup 1985, Hogan
et al. 2019, Kleiner et al. 2019). Vanhornia guizhouensis is found
in China and Thailand (Artmann-Graf 2016, He & Chu 1990).
Vanhornia leileri is a Palaearctic species that was first described
by Hedqvist in 1976 and is known from Sweden, Switzerland,
Germany, Eastern Russia and now also from the Netherlands
(Artmann-Graf 2016, Doczkal 2017, He & Xu 2015, Hedqvist
1976). An identification table for the three species of the genus
Vanhornia is given in He & Xu (2015).
We propose the name ‘dwarskaakwespen‘ as the Dutch
name for the family Vanhorniidae and ‘Europese dwarskaak-
wesp’ for the species Vanhornia leileri, based on the distinctive
mandibles (see description below).
Material Province of Gelderland: Wageningen (51.966°N 5.674°E),
two females collected from skylight, 26.vi.2019, leg. D. Belgers,
det. Th. Peeters, 1 / col. Natuurmuseum Brabant, Tilburg & 1 /
col. Naturalis Biodiversity Center, Leiden.
Description
The following description is largely taken from Hedqvist (1976).
Female length 4 mm, thereby the two females collected in the
Netherlands are slightly smaller than the 4.5 mm sized female
described in Hedqvist (1976) (figure 3a). Colour black, legs and
tegulae yellowish brown and antenna brown. Wing veins black
(figure 3b). The entire body with short white setae. Head with
85
entomologische berichten
80 (3) 2020
1. Habitus female Vanhornia leileri (4 mm), (a) dorsal side and (b) lateral side. Wageningen (province of Gelderland), 26.vi.2019. Photos: Dick
Belgers
1. Habitus vrouwtje Vanhornia leileri (4 mm), (a) dorsale zijde en (b) laterale zijde. Wageningen (Gelderland), 26.vi.2019.
scattered punctuation (figure 3c-d). Mandibles with 5 teeth
(figure 3c-d). Antennae 13-jointed, inserted near the base of
clypeus. Clypeus with anterior margin shallowly emarginate.
Occiput with a carina. Notauli strong with large pits. Scutellar
fovea deep with carinae, scutellum smooth. Propodeum rugose
with tooth-like processes. Petiole short, transverse. Gaster with
the tergites fused into a carapace, basally truncate with a trans-
verse carina from which arise longitudinal carinae of which the
most striking is the mid keel (figure 3f). The carinae reach 2/3
of the carapace, areas between the carinae punctate. Ovipositor
longer than gaster (figure 3e-f). Legs with no visible second tro-
chanter, hind tibia with one spur.
A special feature of Vanhornia are the exodont mandibles,
opening outwards and not overlapping (figure 3c-d). Exodont
mandibles are rare in insects, occurring only in Vanhornia, in
braconids of the subfamily Alysiinae, and in some larval Eucne-
midae (Deyrup 1985, Griffiths 1964, Muona 2010). The adaptive
significance of the exodont mandibles of Vanhornia is unknown
(Deyrup 1985). They are probably a kind of tool that is used
during the emerging of the adult from the pupal chamber of
the host. This is also the case with other species with exodontal
mandibles such as species of the subfamily Alysiinae (family
Braconidae) (Griffiths 1964). Van Horn (1909) (in Deyrup 1985)
described the action of the mandibles from a Melasis pectinicornis
(Eucnemidae) larvae as saw-like, suitable for the slit-like
galleries that the larvae construct in dead wood. Adult eucne-
mids which, like Vanhornia, need only to escape from the pupal
chamber, have normal mandibles (Deyrup 1985).
Another interesting aspect is the ovipositor of Vanhornia.
Deyrup (1985) reports that when it is not in use, it is bent for-
ward at the base so as to lie in a groove along the ventral side
of the gaster. This groove is not nearly long enough to hold the
ovipositor, which is about the same length as the entire insect
(figure 3f). The ovipositor of V. eucnemidarum is 5.8 mm long and
unusually thin, about 0.05 mm (Deyrup 1985). For the collected
Dutch female specimens, the externally visible ovipositor is
2.5 mm long, measured from the tip of the abdomen. The tip of
the ovipositor is highly flexible, and its delicate probing resembles
that of the tip of a moth’s proboscis seeking nectar (Deyrup
1985). The functional morphology of the ovipositor is unknown,
but it is probably not used in the same way as the long, wood-
drilling ovipositor of certain Ichneumonidae and Braconidae
(Deyrup 1985).
a b
2. Skylights over an outside terrace
where Vanhornia leileri was collected.
Photo: Dick Belgers
2. Lichtkoepels boven een buitenterras
waar de Vanhornia leileri exemplaren zijn
aangetroffen.
86 entomologische berichten
80 (3) 2020
Biology
Hedqvist (1976) has reared both V. leileri specimens (one female
and one male) from the false click beetle Hylis cariniceps (Reitter)
(Eucnemidae). The Nearctic species, V. eucnemidarum also uses
beetles from the Eucnemidae family as a host: Isorhipis ruficornis
(Say) (Deyrup 1985). There are eight Eucnemidae species in the
Netherlands (Cuppen 2010, Heijerman & Thomas 2016). These
belong to five genera: Melasis buprestoides (Linnaeus), Hylis with
three species, Microrhagus with two species, Eucnemis capucina
Ahrens and Dromaeolus barnabita (Villa & Villa). All species are
rare, except Melasis bupresoides which can be regarded as fairly
common. It is interesting to note that on 10th of June 2019,
two weeks before the V. leileri specimens collection, a female
Microrhagus lepidus Rosenhauer, was collected from the same
skylights (leg. D Belgers, det. & col. J Burgers) (figure 4). Hylis
cariniceps has not been found in the Netherlands since 1966
and was previously only observed in the province of Limburg
(Cuppen 2010). The larvae of most Eucnemidae species develop
in decayed wood from deciduous trees and sometimes from
coniferous trees (Moraal et al. 2003). The development is usually
two-year, but sometimes adults of the same population emerge
after three to four years. Larvae usually move remarkably slowly
3.Vanhornia leileri, female (same specimen as in figure 1): (a) habitus dorsal side, (b) fore wing, (c) head frontal side, (d) head dorsal side, (e) habi-
tus ventral side, and (f) abdomen lateral side. Photos: Wim Klein
3. Vanhornia leileri, vrouw (zelfde individu als in figuur 1): (a) habitus dorsaal, (b) voorvleugel, (c) kop frontaal, (d) kop dorsaal, (e) habitus ventraal,
en (f) achterlijf lateraal.
a b
c d
e f
87
entomologische berichten
80 (3) 2020
and live in soft and moist wood layers under a harder outer
layer (Moraal et al. 2003). They probably do not feed on wood but
on wood fungi (Leiler 1976, Muona & Teräväinen 2008). Townes
& Townes (1981) reported an observation of the ovipositor of
V. eucnemidarum being passed along a crack in a hardwood log.
Deyrup (1985) notes that the structure of the ovipositor of
Vanhornia suggest that the host is attacked when it is an egg
or as a young larva that has not tunnelled far into the wood.
There is very little information about the life history of V. leileri.
So far only adult specimens of this species have been found.
Deyrup (1985) found two specimens of V. eucnemidarum, one
male and one female, which emerged from pupal cells of
Isorhipis rujicornis in a dead maple tree. The complete larval skin
of the host was found in the cells from which the parasitoid
emerged. There was no cocoon or visible lining in the cell. The
position of the V. eucnemidarum pupa with respect to that of the
dead host larva was unclear.
The flight activity of adult V. eucnemidarum in North America
is from mid-May to the end of July (Smith 1995). Hedqvist (1976)
found the Swedish V. leileri specimens on July 25 and the Swiss
sighting was on August 5 (Artmann-Graf 2016). The two German
specimens were collected between June 20 and the 6th of July
(Doczkal 2017). The Dutch observation was made on June the
26th. The flight activity of V. eucnemidarum in North America
is therefore broadly in line with the flight activity of V. leileri in
Europe, with the note that the North American species data
consists of 281 specimens (Hogan et al. 2019) and the European
species only of seven specimens.
Discussion
With five European records and only seven collected specimens,
we can assume that V. leileri is a rare species. It seems very un-
likely that this interesting wasp has reached the Netherlands
through an area expansion caused by climate-change. The scar-
city of specimens is probably due to the rarity of the species.
If the host is attacked only as an egg or newly hatched larva,
the shortness of opportunity provided for V. leileri, combined
with a hidden and possibly rare host, might explain the rarity
of this species. So far little is known about the host use and
the number of host species of V. leileri. Eucnemidae larvae are
not easily found by entomologists. However if we want to gain
more knowledge about the life history of this very interesting
parasitoid wasp it is important to find and study larval/pupal
cells of false click beetles in dead wood. Through improved
forest management, with increased presence of lots of dead and
decaying wood, it is expected that the biodiversity of forests will
increase significantly. Vanhornia leileri should be able to benefit
from these measures because it is directly dependent on false
click beetle larvae, which only live in dead wood.
Acknowledgements
We thank Lars Krogmann and Kees Zwakhals for providing
some essential references and Fiona Zachariasse for her correc-
tions and comments.
4. Female Microrhagus lepidus, habitus dorsal side. Wageningen (prov-
ince of Gelderland), 10.vi.2019. Photo: Dick Belgers
4. Vrouw Microrhagus lepidus, habitus dorsaal. Wageningen (Gelderland),
10.vi.2019.
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Accepted: February 6, 2020
Samenvatting
Vanhornia leileri, een nieuwe soort en nieuwe familie voor Nederland (Hymenoptera:
Vanhorniidae)
Uit twee lichtkoepels, gesitueerd in een overkapping tussen een huis en een schuur in
Wageningen, werden op 26 juni 2019 twee vrouwtjes van Vanhornia leileri verzameld.
Vanhornia leileri is de enige Europese vertegenwoordiger van de Vanhorniidae, een familie
die niet eerder uit Nederland werd gemeld. Vanwege de opmerkelijke kaken die naar buiten
staan wordt de naam ‘dwarskaakwespen’ voorgesteld voor de familie Vanhorniidae en
Europese dwarskaakwesp voor de nieuw ontdekte soort. Vanhornia leileri is een parasitoïde
wesp van schijnkniptorren (Eucnemidae) en is nu bekend uit vijf Europese landen. In het
verspreidingsgebied zijn in totaal maar zeven individuen verzameld waardoor de soort
als zeer zeldzaam wordt beschouwd. Een interessant aspect is de uiterst lange en dunne
legboor van V. leileri. Wanneer de legboor niet in gebruik is, wordt deze in een groef langs
de buikzijde van het achterlichaam gehouden. Over de levensgeschiedenis van V. leileri
is weinig bekend. Wel is bekend dat ze rechtstreeks afhankelijk is van schijnkniptorren
waarvan de larven in dood hout leven. Door verbeterd bosbeheer, met een verhoogde
aanwezigheid van dood en rottend hout, wordt verwacht dat de biodiversiteit van bossen
aanzienlijk zal toenemen. Vanhornia leileri zou van deze maatregelen moeten kunnen
profiteren.
Dick Belgers
Wageningen
dick.belgers@wur.nl
Wim Klein
Breda
Theo Peeters
Tilburg
