Review of the Megastigmidae in Belgium and the Netherlands (Hymenoptera: Chalcidoidea)

Abstract

In this paper, we provide an overview of the seed chalcid wasps Bootanomyia spp. and Megastigmus spp. (Hymenoptera: Megastigmidae) in both Belgium and the Netherlands. Sixteen species, including six non-natives to Europe, are reported after checking over a thousand specimens. The European species Megastigmus aculeatus (Swederus, 1795) and M. suspectus Borries, 1895 are reported for the first time in Belgium. The European species Bootanomyia stigmatizans (Fabricius, 1798), Megastigmus rosae Bouček, 1971 and Megastigmus strobilobius Ratzeburg, 1848, and the Nearctic species Megastigmus atedius Walker, 1851 and Megastigmus lasiocarpae Crosby, 1913 (only the second report in Europe) are new for the Netherlands. Novel insights are offered on the ecology, morphology and phenology of Megastigmus aculeatus, Megastigmus nigrovariegatus and Megastigmus rosae.

Full text

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– 65 –
Revue d’Hyménoptérologie
Journal of Hymenopterology
https://doi.org/10.47446/OSMIA
Volume 11
2023
ARTICLE
Review of the Megastigmidae in Belgium and the
Netherlands (Hymenoptera: Chalcidoidea)
Fons VERHEYDE1 • Sandrine ULENBERG2 • Hilco MEIJER 3 • Paul HOEKSTRA4 •
Augustijn DE KETELAERE 5 • Alain ROQUES6
VERHEYDE, F., S. ULENBERG, H. MEIJER, P. HOEKSTRA, A. DE KETELAERE & A. ROQUES (2023). Review of the Megastigmidae in Belgium and the Netherlands
(Hymenoptera: Chalcidoidea). Osmia, 11: 65–80. https://doi.org/10.47446/OSMIA11.10
Abstract
In this paper, we provide an overview of the seed chalcid wasps Bootanomyia spp. and Megastigmus spp. (Hymenoptera:
Megastigmidae) in both Belgium and the Netherlands. Sixteen species, including six non-natives to Europe, are reported after
checking over a thousand specimens. The European species Megastigmus aculeatus (SWEDERUS, 1795) and M. suspectus BORRIES,
1895 are reported for the first time in Belgium. The European species Bootanomyia stigmatizans (FABRICIUS, 1798), Megastigmus
rosae BOUČEK, 1971 and Megastigmus strobilobius RATZEBURG, 1848, and the Nearctic species Megastigmus atedius WALKER, 1851
and Megastigmus lasiocarpae CROSBY, 1913 (only the second report in Europe) are new for the Netherlands. Novel insights are
offered on the ecology, morphology and phenology of Megastigmus aculeatus, Megastigmus nigrovariegatus and Megastigmus
rosae.
Keywords | Seed wasps • Chalcid wasps • invasive species • Low Countries • biodiversity
Révision des Megastigmidae de Belgique et des Pays-Bas (Hymenoptera : Chalcidoidea)
Résumé
Dans cet article, nous proposons une vue d’ensemble sur les guêpes chalcidienne parasites des semences des genres Bootanomyia
spp. et Megastigmus spp. (Hymenoptera : Megastigmidae) de Belgique et des Pays-Bas. Seize espèces, dont six non-natives
d’Europe, sont décrites après examen d’un millier de spécimens. Les espèces européennes Megastigmus aculeatus (SWEDERUS,
1795) et Megastigmus suspectus BORRIES, 1895 sont décrites pour la première fois en Belgique. Les espèces européennes
Bootanomyia stigmatizans (FABRICIUS, 1798), Megastigmus rosae BOUČEK, 1971 et Megastigmus strobilobius RATZEBURG, 1848, ainsi
que les espèces néarctiques Megastigmus atedius WALKER, 1851 et Megastigmus lasiocarpae CROSBY, 1913 (deuxième mention
pour l’Europe) sont nouvelles pour les Pays-Bas. De nouvelles perspectives sont proposées concernant l’écologie, la morphologie
et la phénologie des espèces Megastigmus aculeatus, Megastigmus nigrovariegatus et Megastigmus rosae.
Mots-clefs | Guêpes parasites des semences • Chalcidiens • espèces invasives • Bénélux • biodiversité
Reçu • Received | 15 December 2022 || Accepté • Accepted | 23 December 2023 || Publié (en ligne) • Published (onlin e) | 24 December 2023
Reviewers | K. MCCORMACK • J.-Y. RASPLUS || https://zoobank.org/BBA7004C-2232-4910-BB03-B38A2E069589
INTRODUCTION
Chalcid wasps (Chalcidoidea) are a huge superfamily of
mostly small parasitoid wasps, consisting of fifty different
families (BURKS et al., 2022). The family Megastigmidae used
to be a subfamily of Torymidae (GRISSELL, 1976; 1995). It was
1 [FV] Aartshertoginnestraat 58/01, B – 8400 Ostende, B elgium • fonsverheyde@hotmail.com
https://orcid.org/0000-0002-2240-9689 • https://zoobank.org/D197B5B4-00FF-4D57-924D-EFF926A99119
2 [SU] Naturalis Biodiversity Center, P.O. Box 9517, NL – 2300 RA Leiden, The Netherlands • sandrine.ulenberg@naturalis.nl
https://orcid.org/0009-0000-9473-2496 • https://zoobank.org/62221791-E1B6-46DC-AD1A-A6C0B4BDFDD2
3 [HM] Boekweitkamp 15, NL – 9203HE Drachten, the Netherlands • h.meyer83@hotmail.com
https://orcid.org/0009-0004-7123-7010 • https://zoobank.org/F91E12D9-E012-4B12-8B70-F4DB162D9FBB
4 [PH] Naturalis Biodiversity Center, P.O. Box 9517, N – 2300 RA Leiden, The Netherlands • Paul.hoekstra@naturalis.nl
https://orcid.org/0000-0002-2155-0963 • https://zoobank.org/AC25A3AB-5DE1-475E-A23C-B159C5D500DD
5 [ADK] Noendre ef 7, B – 8730 Beernem, Belgium • augustijn.de.ketelaere@gmail.com
https://orcid.org/0009-0007-0260-5483 • https://zoobank.org/AE6080BC-053D-4F03-9E4C-1EE483E50C7F
6 [AR] INRAE Zoologie Forestière, 2163 avenue de la Pomme de Pin, F – 45075 Orléans Cedex 2, France • alain.roques@inra.fr
https://orcid.org/0000-0002-3734-3918 • https://zoobank.org/9B88E8F8-6E26-4DBD-952E-6E29AFF7C5AA
only recently reinstated as a valid family (JANŠTA et al., 2018)
with more clearly defined subfamilies (BURKS et al., 2022).
Belonging to Megastigminae, important characteristics for
the subfamily are the knobbed stigma, which is usually

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higher than wide, the rather yellowish body, which
sometimes has metallic colours, the relatively short hind
coxa, which is not more than two times the length of the mid
coxa and the long ovipositor, which is often longer than the
metasoma (BOUČEK, 1988, NIKOL’SKAYA & ZEROVA, 1988;
GRISSELL, 1995, 1997; JANŠTA et al., 2018). More remarkable is
the ecology of most species. Within the Western Palaearctic,
two genera occur: Bootanomyia spp. and Megastigmus spp.
The former genus mainly consists of larval parasitoids of
various gall forming species of Cynipidae (Hymenoptera),
while the latter genus is associated with seeds of shrubs and
trees (for cases and examples see Results). Morphologically,
Bootanomyia spp. can be distinguished from Megastigmus by
the body which is at least partially iridescent, the medially
excised or emarginated lower clypeal margin and the
midlobe of the mesoscutum which has at least 4 longitudinal
rows of setae (more details see DOĞANLAR, 2011).
The oldest specimens we report date back to the 19th
century and were collected by (locally) well known
entomologists such as the Belgian Jules TOSQUINET (1824–
1902) (PAULY, 2001). Private collections would still be very
important in the XXth century; examples are those of
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Adolphe CRÈVECOEUR (1895–1959) in Belgium (figure 3) and
Theo GIJSWIJT (1927–2015) in the Netherlands. Only at the
end of the century more attention was paid to
Megastigmidae by government agencies or universities. This
is mainly because these wasps had attracted some attention
as possible invasive ‘pest’ species (i.e., MAILLIEUX et al., 2008;
PAULSON et al., 2014), but also because many of the species
can in fact be found on foreign trees in tree gardens or
arboreta. In the history of both Belgium and the
Netherlands, only the Dutch entomologist Johannes Th.
OUDEMANS (1862–1934) can be seen as someone who has
done systematic research on the subject spanning several
decades (figure 1). OUDEMANS managed the estate ‘Landgoed
Schovenhorst’ in the province of Gelderland (Putten) for
many years. It can still be visited and has many non-native
tree species in its arboretum (figure 2). In the 1930s, when
OUDEMANS collected most of his specimens, he was already a
renowned entomologist. Still, it is noteworthy that for three
species (M. pinus, M. specularis and M. suspectus) our records
from the Netherlands are mostly or even solely based on
records from his arboretum. In recent years, most records
come from isolated findings in Malaise trap projects, or from
citizen science portals (see Results).
Figure 1. J. T. OUDEMANS in estate Landgoed Schovenhorst.
Figure 2. Arboretum of estate Landgoed Schovenhors in Putten.
MATERIAL AND METHODS
To gather our data, all available sources were used. First, we
checked all published data in the literature. Secondly, we
checked the historical collections of the national institutes:
Royal Belgian Institute of Natural Sciences (RBINS) in
Brussels and Naturalis (RMNH) in Leiden. Thirdly,
contemporary material was collected by the authors and
other observers. Finally, we used open data from the citizen
science portals Waarnemingen.be and Waarneming.nl (with
the ObsID as unique identifier). These data were validated by
the first author and were especially useful for some common
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Map 1. Overview of the records in the used dataset 1858–2021.
Legend for this all the maps: purple / orange = before / from 2000. Map M. ISSERTES (QSIG).
species. In the complete dataset, 295 records of 1049
specimens were gathered across Belgium and the Netherlands
(map 1). For the purposes of readability (duplicated data, very
common species), we have integrated this material only
partially in the results section. The first report and the four
most recent ones are mentioned. When we did not include
data, this was mentioned with ‘[…]’. Rearing data discussed in
the remarks-section consists of validated data from the full
dataset. This full dataset can be found linked to the article on
the ResearchGate-page of the first author. References from the
dataset are also integrated in the literature part of this article.
Repositories of collected material (“coll.”) are abbreviated as
follows for institutes: RBINS (Royal Belgian Institute of Natural
Sciences, Brussels), RMN H (Naturalis, Leiden); and for persona l
collections: ADK (Augustijn DE KETELAERE), AR (Alain ROQUES),
FV (Fons VERHEYDE), HM (Hilco MEIJER), PH (Paul HOEKSTRA),
PNL (Pierre-Nicolas LIBERT) and TP (Theo PEETERS).
Distribution maps were made with the open software QGIS
3.26.3 by Mehdi ISSERTES. Where possible, we used GPS-
coordinates and included those in the dataset and results
below. If those were not available, we used the county or city
centre. Estimated coordinates are marked with orange in the
dataset.
RESULTS
Bootanomyia GIRAULT, 1915
Bootanomyia dorsalis (FABRICIUS, 1798)
Material examined. BELGIUM (24 ♀♀, 2 ♂♂ ) • 1 ♀, Gent, 4.VI.1868,
J. TOSQUINET leg., coll. RBINS, reared ex ‘C. foecundatrix’, F. VERHEYDE det.
[…]; 1 ♀, Moeskroen, 50.735 – 3.214, 17 VIII 2020, C. GRUWIER leg.,
ObsID: 198614888, light trap, F. VERHEYDE det.; 1 ♂, Buggenhout, 51.023
– 4.220, 23.V.2021, L. VERHELST leg., ObsID: 214628498, F. VERHEYDE det.;
1 ♀, Buggenhout, 51.023 – 4.220, 2.VI.2021, L. VERHELST leg., ObsID:
215718611, F. VERHEYDE det.; 1 ♀, Buggenhout, , 51.023 – 4.220,
5.VI.2021, L. VERHELST leg., ObsID: 216029633, F. VERHEYDE det.
THE NETHERLANDS (54 ♀♀, 30 ♂♂, 2 indet.) • (min.) 1 ♀ 1 ♂,
Driebergen, VI.1858, G. A. SIX leg., SIX 1859 […]; 1 ♀ 1 ♂, Noordenveld,
53.012 – 6.401, 6.VI.2020, JAN HENK leg., ObsID: 194239878 &
194239910, P. HOEKSTRA det.; 1 ♀ 10 ♂♂, Almere, 52.384 – 5.237,
9–14.III.2021 (galls collected 22.II.2021), P. HOEKSTRA leg., coll. PH
(ObsID: 208771913 & 208895376), reared indoors ex Andricus
coriarius, P. HOEKSTRA det.; 1 ♀, Amstelveen, 52.314 – 4.820, 15.VI.2021,
J. HEIJNEN leg., ObsID: 232435047, F. VERHEYDE det.; 1 ♀, Westerveld,
52.782 – 6.374, 21 VII 2021, J. HEIJNEN leg., ObsID: 232940190, reared ex
?, A. DE KETELAERE det.
Distribution (map 1). European. One of the most common
species we report, with the oldest records (1858 and 1868)
for the family. Widespread in both countries, especially
where oaks are planted. As Andricus spp. are important hosts
(see below) oaks planted at the borders of forests, or solitary
trees, are often visited.
North Sea
English
Channel
France
Great
Britain
Germany
Luxembourg
Belgium
The Netherlands
Legend for all the
maps of this item
before 2000
from 2000

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Map 2. Distribution of Bootanomyia dorsalis.
Map M. ISSERTES (QSIG).
Figure 3. Notes of the Belgian entomologist CRÈVECOEUR,
mentioning B. dorsalis (Sint-Andries, 1943). RBINS.
Remarks. The species (-complex; cf. infra) is well
documented and has several rearing records, all hosts
belonging to the family of Cynipidae associated with
Quercus L. sp. Among the hosts reported are Andricus aries
(GIRAUD, 1859) (1 ×), Andricus coriarius (HARTIG, 1843) (1 ×),
Andricus foecundatrix (HARTIG, 1840) (1 ×) and Andricus
grossulariae GIRAUD, 1859 (1 ×). The main hosts are Andricus
kollari (HARTIG, 1843) (8 ×) (figure 3) and Biorhiza pallida
(OLIVIER, 1791) (4 x). Finally, there is one uncertain report of
Cynips quercusfolii LINNAEUS, 1758 as a host. Some reports
mention specimens being reared just from an oak branch
(Quercus L. sp.). It is important to note there are several
cryptic lineages within the species-complex which may lead
to taxonomic changes in the near future (NICHOLLS et al.,
2017).
Figure 4. a–b. Habitus (a) and frontal view (b) of Bootanomyia
dorsalis (female). Coll. FV. Photo B. MINNEBO.
Bootanomyia stigmatizans (FABRICIUS, 1798)
Material examined. THE NETHERLANDS (1 ♂) • 1 ♂ Almere, 52.384
– 5.237, 9–11.III.2021 (galls collected 22.II.2021), P. HOEKSTRA leg., coll.
PH (ObsID: 208771912), reared indoors ex Andricus coriarius,
P. HOEKSTRA det.
Distribution (map 3). European. Known from only one
locality.
Remarks. One specimen was reared together with
specimens of B. dorsalis. Being over 5 mm, this species has a
distinctive size in comparison to the abovementioned
species (ROQUES & SKRZYPCZYŃSKA, 2003).
Megastigmus DALMAN, 1820
Megastigmus aculeatus (SWEDERUS, 1795)
Material examined. BELGIUM (20 ♀♀) • 1 ♀, Evere, 50.879 – 4.391,
16.VI.2008, B. HANSSENS leg., ObsID: 40099448, F. VERHEYDE & J. CORTENS
a
b

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– 69 –
Map 3. Distribution of Bootanomyia stigmatizans.
Map M. ISSERTES (QSIG).
Map 4. Distribution of Megastigmus aculeatus.
Map M. ISSERTES (QSIG).
det. […]; 1 ♀, Nassogne, 50.127 – 5.357, 13.VII.2021, M. VALDUEZA leg.,
ObsID: 206973319, F. VERHEYDE det.; 1 ♀, Roeselare, 50.944 – 3.116,
13.VI.2021, M. VALDUEZA & F. VERHEYDE leg., coll. FV, ObsID: 216923957,
F. VERHEYDE det.; 4 ♀♀, Châtelet, 50.406 – 4.532, 20 VI 2021, E. LECLERCQ
leg., ObsID: 221612646, F. VERHEYDE det.; 1 ♀, Hever, 50.991 – 4.528,
20.VI.2021, R. SEGERS leg., ObsID: 221612646, F. VERHEYDE det.
THE NETHERLANDS (93 ♀♀ 1 ♂) • 1 ♀, Bloemendaal –
Kennemerduinen, 20.V.1967, M. J. GIJSWIJT leg., coll. RMNH & GIJSWIJT,
2003, reared ex Rosaceae, T. GIJSWIJT det. […]; 1 ♀, Rotterdam, 51.927 –
4.498, 24.VI.2021, M. SNIJDER leg., ObsID: 218237964, F. VERHEYDE det.;
1 ♀, Land van Cuijk, 51.709 – 5.943, 26.VI.2021, P. SMEETS leg., ObsID:
218266883, F. VERHEYDE det.; 1 ♀, Oegstgeest, 52.182 – 4.476,
16.VII.2021, B. DIJKSTRA leg., ObsID: 234896036, F. VERHEYDE det.; 2 ♀♀,
Oegstgeest, 52.712 – 6.296, 8 VIII 2021, J. ESSINK leg., ObsID: 222424826,
F. VERHEYDE det.
Distribution (map 4). European. The most commonly
reported species from the family in recent years. The species
was caught in three recent (2021–2022) MALAISE trap
projects from different localities in Belgium and the
Netherlands. It is associated with Rosaceae JUSS. (see below)
and, as a consequence, it is perhaps more visible as these
plants tend to be lower to the ground and planted in
gardens, parks and urban environments. Before 1967, there
are no records available, suggesting the species has
succeeded in colonizing new areas in recent decades.
Figure 5. Diagram of phenology of M. aculeatus and M. rosae.
A: absolute numbers. R: per occurrence.
Remarks. As mentioned above, M. aculeatus but also M.
rosae [see below; incl. M. nigrovariegatus] are species
associated with Rosaceae. At least two cases of rearing are
known from the Low Countries. Among the reported host
plants are Rosa rugosa THUNB., but other unidentified
Rosaceae were also used. In some gardens many specimens
could be observed in detail throughout the year (e.g., pers.
obs. of B. HANSSENS in Belgium and H. JANSEN in the
Netherlands). Interestingly, in one garden in the
Netherlands, both M. aculeatus and M. rosae were present
and observed on a daily basis. We know there are clear
differences in morphology (figures 6 vs. 8–10 for M. rosae),
but these observations demonstrate that the phenology also
differs. This is confirmed by all other data we have on both
species. M. aculeatus clearly peaks in June, while M. rosae is
only scarcely found at that moment of the year and peaks
around August (figure 5). The obvious difference in
phenology may explain how both species survive in more or
less the same ecological niche. Males appear to be very rare
for both species. Possibly, the species is partially thelytokous
(see also our discussion on M. rosae).
Megastigmus atedius WALKER, 1851
Material examined. THE NETHERLANDS (1 ♀ + 1 ♀?) • 1 ♀?,
Nunspeet – Veluwe, 23.III.1989, M. J. GIJSWIJT leg., coll. RMNH, reared
ex Picea abies, T. GIJSWIJT det. […]; 1 ♀, Olterterp, 53.070 – 6.106,
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140
120
100
80
60
40
20
0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
M. aculeatus (R) M. aculeatus (A) M. rosae (R) M. rosae (A)

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Figure 6. Habitus of Megastigmus aculeatus (female). Coll. FV. Photo B. MINNEBO.
Map 5. Distribution of Megastigmus atedius.
Map M. ISSERTES (QSIG).
23.V.2021, H. MEIJER leg., coll. HM, A. ROQUES, H. MEIJER & F. VERHEYDE
det.
Distribution (map 5). Nearctic. The species is now
confirmed and first reported for the Low Countries. It was
found in the Netherlands by HM in the vicinity of conifers.
Remarks. This is one of the originally Nearctic species
imported to Europe and associated with several introduced
conifers. It is already known from many neighboring
countries including Denmark, France and Germany (ROQUES
& SKRZYPCZYŃSKA, 2003). In the collection of RMNH, we
found one uncertain specimen, reared from cones of P. abies
(L.) H. KARST. The recent specimen collected in 2021 near
foreign Picea spp. was carefully identified using the key of
ROQUES & SKRZYPCZYŃSKA 2003.
Megastigmus bipunctatus (SWEDERUS, 1795)
Material examined. THE NETHERLANDS (1 ♀) • 1 ♀, Hattem,
28.VI.1993, B. VAN AARTSEN leg. (GIJSWIJT, 2003).
Distribution (map 6). European. Very rare and known from
only one report in the Netherlands, dating from 1993
(GIJSWIJT, 2003). Host plants are Juniperus L. spp. The species
can be expected near sandy heathlands where J. communis L.
is more common. In Belgium, this will be mainly constricted
to the province of Limburg in Flanders and the south-eastern
parts of the country. In the Netherlands, the plant is slightly
more widespread, starting from central Netherlands to the
whole eastern part of the country. It is expected to be
underreported.
Remarks. With the host plant known, it can only be
confused with the extralimital and Mediterranean
M. amicorum BOUČEK, 1969; but there are clear
morphological differences and its presence is more unlikely
in our countries (ROQUES & SKRZYPCZYŃSKA, 2003).
Megastigmus brevicaudis RATZEBURG, 1852
Material examined. THE NETHERLANDS (2 ♀♀) • 1 ♀, ‘s Graveland,
7.VII.1962, M. J. GIJSWIJT leg., coll. RMNH (GIJSWIJT, 2003); 1 ♀, Kootwijk,
27.V.1967, M. J. GIJSWIJT leg., coll. RMNH (GIJSWIJT, 2003).
Distribution (map 7). European. Just as the
abovementioned M. bipunctatus it is very rare, and only
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Map 6. Distribution of Megastigmus bipunctatus.
Map M. ISSERTES (QSIG).
Map 7. Distribution of Megastigmus brevicaudis.
Map M. ISSERTES (QSIG).
known from two older reports in the sixties from the
Netherlands (GIJSWIJT, 2003).
Remarks. In contrast to M. bipunctatus, the hosts plants are
more abundant: Amelanchier MEDIK. and Sorbus L. spp. It is
the only species associated with these plants in the West
Palearctic (ROQUES & SKRZYPCZYŃSKA, 2003). With
S. aucuparia L. as a plausible host plant this species appears
to be genuinely rare; otherwise, it may have turned up in
non-selective insect traps such as Malaise or pan traps.
Megastigmus lasiocarpae CROSBY, 1913
Material examined. THE NETHERLANDS (1 ♀) • 1 ♀, Olterterp,
53.070 – 6.106, 30.IV.2022, H. MEIJER leg., coll. HM, H. MEIJER, F. VERHEYDE
& A. ROQUES det.
Distribution (map 8). Nearctic. This is only the second
finding of this species (figure 7) in Europe and therefore
extremely rare. It was reported in Finland in 1969 (ANILLA,
1970).
Map 8. Distribution of Megastigmus lasiocarpae.
Map M. ISSERTES (QSIG).
Remarks. It is associated with Nearctic Abies MILL. spp.
(ROQUES & SKRZYPCZYŃSKA, 2003).
Megastigmus milleri MILLIRON, 1949
Material examined. BELGIUM (1 ♀) • 1 ♀, Gesves, 2006, reared ex
Abies grandis (ROZENBERG et al., 2006; GBIF). THE NETHERLANDS (8 ♀♀,
7 ♂♂) • 8 ♀♀, 7 ♂♂, Sleenerzand, IV–V.1990, P. GRIJPMA leg., coll.
RMNH, reared ex Abies grandis, GIJSWIJT, 2003.
Distribution (map 9). Nearctic. Known from only one
locality in Namur (Belgium) and from one in Drenthe (the
Netherlands), presumably on foreign conifers.
Remarks. Another Nearctic species. All specimens have
been reported on the exotic Abies grandis (DOUGLAS ex D.
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Figure 7. Habitus of Megastigmus lasiocarpae (female). Photo A. ROQUES.
Map 9. Distribution of Megastigmus milleri.
Map M. ISSERTES (QSIG).
DON) LINDL. It can thus be expected on similar conifers, more
specifically firs (Abies spp.).
Megastigmus pictus (FÖRSTER, 1841)
Material examined. THE NETHERLANDS (18 ♀♀, 2 ♂) • 18 ♀♀, 1 ♂,
Vaals, III–IV.1986, P. GRIJPMA leg., coll. RMNH, reared ex L. decidua and
L. leptolepis (syn. kaempferi) (GRIJPMA & VAN DE WEERD, 1991; GIJSWIJT,
2003); 1 ♂, Vaals (seed orchard), 14.VII.1990, P. GRIJPMA leg., coll. AR,
reared ex L. leptolepis, ROQUES & SKRZYPCZYŃSKA, 2003.
Distribution (map 10). European, but more specifically
Eurasian. Only reported from one locality in the Netherlands
(see also GRIJPMA & VAN DE WEERD, 1991), but several
specimens are preserved.
Remarks. Associated with conifers, and more specifically
Larix spp. (ROQUES & SKRZYPCZYŃSKA, 2003). Larches are non-
native species but commonly planted throughout Belgium
and the Netherlands (especially Larix kaempferi (LAMB.)
CARRIÈRE or hybrids with Larix decidua MILL.). Higher
densities are reached on sandy soil near heathlands. This
would suggest M. pictus is introduced but underreported, or
other unknown (environmental) factors are important for
stable populations (for example a closer association with a
host tree species, i.e. L. decidua).
Megastigmus pinus PARFITT, 1857
Material examined. BELGIUM (8 ♀♀, 9 ♂♂) • 8 ♀♀, 9 ♂♂, Vielsalm,
1993, F. TOMBYUSES leg., coll. AR, reared ex Abies procera (ROQUES &
SKRZYPCZYŃSKA, 2003). THE NETHERLANDS (46 ♀♀, 37 ♂♂) • 4 ♀♀,

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Map 10. Distribution of Megastigmus pictus.
Map M. ISSERTES (QSIG).
Map 11. Distribution of Megastigmus pinus.
Map M. ISSERTES (QSIG).
Putten – Schovenh orst (Arboretum), V.1930, J. Th. OUDEMANS leg., coll.
RMNH, reared ex Abies grandis (OUDEMANS, 1933); 1 ♀, 1 ♂, Putten –
Schovenhorst (Arboretum), 12–13.V.1931, J. Th. OUDEMANS leg., coll.
RMNH, reared ex Abies grandis (OUDEMANS, 1933); 5 ♀♀, Putten –
Schovenhorst (Arboretum), V.1932, J. Th. OUDEMANS leg., coll. RMNH,
reared ex Abies grandis (OUDEMANS, 1933); 8 ♀♀, 12 ♂♂, Putten –
Schovenhorst (Arboretum), 10–20.IV.1936, J. Th. OUDEMANS leg., coll.
RMNH, reared ex Abies magnifica; 28 ♀♀, 24 ♂♂, Putten –
Schovenhorst (Arboretum), 1936, WUR leg., coll. RMNH, reared ex
Abies concolor, A. grandis and A. lowiana.
Distribution (map 11). Another Nearctic species. Many
specimens are available, but the species is known from only
one locality in both countries.
Remarks. The species has been reared from many Abies spp.,
most of them by the Dutch entomologist OUDEMANS in the
1930s (figure 1). Among the cases reported are exotic Abies
spp. such as A. concolor (GORDON & GLEND.) LINDL. Ex Hildebr.
(2 ×), A. grandis (DOUGLAS ex D. DON) LINDL. (4 ×),
A. magnifica A. MURRAY bis (1 ×) and A. procera REHDER (1 ×).
Megastigmus rafni HOFFMEYER, 1929
Material examined. BELGIUM (1) • Min. 1 ex., locality unknown,
Belgium Forestry Office (AR) leg., reared ex Abies concolor (ROQUES &
SKRZYPCZYŃSKA, 2003). THE NETHERLA NDS (10 ♀♀, 21 ♂♂) • 4 ♂♂, Ede,
XI-XII.1970, W. C. NIJVELDT leg., coll. RMNH, reared ex Picea abies
(discussion see below) (GIJSWIJT, 2003); 7 ♀♀, 10 ♂♂, Sleenerzand,
V.1989, P. GRIJPMA leg., coll. AR, reared ex Abies grandis (ROQUES &
SKRZYPCZYŃSKA, 2003); 3 ♀♀, 7 ♂♂, Sleenerzand, V-VI.1990, P. GRIJPMA
leg., coll. RMNH, reared ex Abies grandis (GIJSWIJT, 2003).
Distribution (map 12). Another species of Nearctic origin.
Known from only few localities in both countries.
Map 12. Distribution of Megastigmus rafni.
Map M. ISSERTES (QSIG).
Remarks. Supposedly rare species, associated with both
European and exotic Abies spp. (ROQUES & SKRZYPCZYŃSKA,
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Figure 8. Habitus of Megastigmus rosae (female). Coll. FV. Photo B. MINNEBO.
Map 13. Distribution of Megastigmus rosae.
Map M. ISSERTES (QSIG).
2003). There is one report from cones of Picea abies. This
rearing record is probably erroneous, analyzing the known
rearing data of this species, which suggests it is strictly
associated with Abies spp. Concerning the distribution,
similarly to M. pictus, we may question whether or not the
species is overlooked.
Megastigmus rosae BOUČEK, 1971
Material examined. THE NETHERLANDS (207 ♀♀) • 1 ♀, Eindhoven,
51.465 – 5.461, 26.VI.2014, M. GUÉGAN leg., ObsID: 85817399,
F. VERHEYDE det. […]; 1 ♀, Berghuizen, 52.712 – 6.296, 12.VI.2020,
A. KRUITHOF & J. ESSINK leg., coll. FV, ObsID: 214797177, A. ROQUES &
S. ULENBERG det.; 11 ♀♀, Berghuizen, 52.712 – 6.296, 31.VIII.2021,
J. ESSINK leg., ObsID: 224438495, F. VERHEYDE det.; 1 ♀, Rijssen-Holten,
52.305 – 6.522, 9.I.2022, G. VAN DE MAAT leg., ObsID: 232796959,
F. VERHEYDE det.
Distribution (map 13). European. Unreported in Belgium,
but the Dutch findings suggest the habitat does not seem to
be specific. In the Netherlands the species is mainly reported
in the eastern half of the country, but this could be a
coincidence as there are only four known localities. It is
known from neighboring countries such as France, Germany
and Denmark (ROQUES & SKRZYPCZYŃSKA, 2003 and
unpublished data).
Remarks. This is one of the most difficult species to identify
(figures 8–10). It can be confused with the Nearctic
M. nigrovariegatus ASHMEAD, 1890, which is highly variable in
color and similar to M. rosae. Therefore, a specimen was sent

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to both SU and AR to confirm identification. There are some
structural characters which can be used to separate our
specimens from that of the abovementioned
M. nigrovariegatus: (a) the scutellum is mostly striate and
not largely reticulate; (b) the frenal area is quite smooth and
not with longitudinal carinae; (c) the upper part of the
stigmal vein is longer than the uncus (same length in
M. nigrovariegatus); (d) usually the infuscate area around the
stigma is larger in M. nigrovariegatus, although variable.
In the Netherlands, confirmed rearings have mainly been
associated with Rosa rugosa THUNB. and incidentally with
Rosa ‘Hollandica’ PERS. ex STEUD. Only one uncertain male
was found in August 2020, but in 2022 AK and JE succeeded
in rearing males (this data was not included in the dataset)
(figure 10). The ratio of males-females reared in comparison
to those that could be found in the garden was 1:3 versus
1:20. Females appeared to be more flexible in flying behavior
and were often seen ovipositing.
Figure 9. Stigma (front wing) of Megastigmus rosae (female).
Coll. FV. Photo B. MINNEBO.
Figure 10. Habitus of Megastigmus rosae (male).
Photo A. KRUITHOF.
Two generations of M. rosae fly in the Netherlands: an early
generation in May and June, and a later one in August. The
abundance of the early generation is low, and probably
represents individuals emerging from infected seeds of the
previous year. Larval diapause is common in Megastigmus
spp. The early generation oviposits in young rose hips in June,
followed by a period in July when individuals are absent. The
late generation emerges in August, during which time
mating and oviposition can be observed. In spite of most
rosehips being mature at this time, oviposition
predominantly occurs in the less common younger rosehips.
Males have not been observed in the early generation,
although we should stress that the abundance of the
generation is low and therefore easier for males simply to
have been missed during sampling. As there are no
observations of males (and logically, mating) early in the
year, we cannot exclude adult diapause at this stage. In the
case of free living or adult diapause, females would only be
fertilized in August and September and hibernate the
following months to emerge again in May and June. One
adult individual was indeed found indoors in January,
suggesting adult or free-living diapause, but it could also
have been triggered by the artificial conditions inside. More
research is needed to say anything definitive on the ecology
of the species.
Megastigmus specularis WALLEY, 1932
Material examined. THE NETHERLANDS (11 ♀♀, 3 ♂♂) • 2 ♂♂, 1 ♂,
Putten – Schovenh orst (Arboretum), V.1930, J. Th. OUDEMANS leg., coll.
RMNH, reared ex Abies cilicica (GIJSWIJT 2003); 3 ♀♀, 2 ♂♂, Putten –
Schovenhorst (Arboretum), IV-V.1931, J. Th. OUDEMANS leg., coll.
RMNH, reared ex Abies sp. (GIJSWIJT, 2003); 1 ♀, Burgum, 53.197 –
5.997, 1.VI.2016, R. VAN DER ROL leg., oviposition on Abies koreana,
ObsID: 119426536, F. VERHEYDE & A. ROQUES det.; 5 ♀♀, Burgum,
53.197 – 5.997, 5.VI.2017, R. VAN DER ROL leg., oviposition on Abies
koreana, ObsID: 139649591, F. VERHEYDE & A. ROQUES det.
Distribution (map 14). Another Nearctic species imported
to Europe and associated with introduced firs. Rare, but
known from neighboring countries such as Denmark and
France (ROQUES & SKRZYPCZYŃSKA, 2003).
Map 14. Distribution of Megastigmus specularis.
Map M. ISSERTES (QSIG).
Remarks. Until recently this species was only known from
one locality in the Netherlands in the 1930s, where it was
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Figure. 11. Habitus of Megastigmus specularis (female) on Abies koreana. Photo R. VAN DER ROL.
Map 15. Distribution of Megastigmus spermotrophus.
Map M. ISSERTES (QSIG).
reared from Abies cilicica (ANTOINE & KOTSCHY) CARRIÈRE; so,
this is clearly one of the more seldomly reported imported
species. In 2016 it was rediscovered in a garden in the
province of Friesland. One year later several individuals were
seen ovipositing on cones of Abies koreana E. H. WILSON
(figure 11).
Megastigmus spermotrophus WACHTL, 1893
Material examined. BELGIUM (8 ♀♀, 7 ♂♂ + 3 min. ex.) • 1 ex.,
Baraque de Fraiture, 1937, J. FOUARGE leg., reared ex Pseudotsuga
menziesii (VAN DEN BRUEL, 1937); 6 ♀♀, 5 ♂♂, Fenffe, V.1993,
F. TOMBUYSES leg., coll. AR, reared ex Pseudotsuga menziesii (ROQUES &
SKRZYPCZYŃSKA, 2003); Min. 2 ex., 2003–2004, reared ex Pseudotsuga
menziesii (MAILLEUX et al., 2008); 1 ♂, Somal, 50.327 – 5.317, 30.III.2018,
P.-N. LIBERT leg., reared ex Pseudotsuga sp. (LIBERT et al., 2020); 1 ♂,
Hotton, 50.238 – 5.423, 24.V.2020, M. VALDUEZA leg., ObsID: 191822316,
F. VERHEYDE det. THE NETHERLANDS (42 ♀♀, 29 ♂♂) • 9 ♀♀, 3 ♂♂,
Apeldoorn - ‘t Loo, 1925, J. Th. OUDEMANS leg., coll. RMNH, reared ex
Pseudotsuga menziesii (OUDEMANS, 1931) […]; 1 ♀, ‘t Harde, 29.V.1992,
B. VAN AARTSEN leg., coll. RMNH, T. GIJSWIJT det.; 1 ♀, Bergen, 52.678 –
4.674, 1.V.2019, T. DE GRAAF leg., ObsID: 171436243, T. DE GRAAF &
P. HOEKSTRA det.; 1 ♀, Tilburg – De Kaaistoep, 51.540 – 5.009, 1.VI.2019,
H. SPIJKERS & P. VAN WIELINK leg., coll. TP, light trap, P. HOEKSTRA det.;
1 ♀, Goirle, 51.522 – 5.076, 3.VI.2021, T. KRUIZE leg., coll. FV, ObsID:
215798723, F. VERHEYDE det.
Distribution (map 15). Although of Nearctic origin, one of
the more common species specifically bound to Pseudotsuga
menziesii (MIRB.) Franco (ROQUES & SKRZYPCZYŃSKA, 2003).
Remarks. Other Hymenoptera species such as the sawfly
Urocerus augur (KLUG, 1803) have been associated with the
same tree species (see observations on Waarnemingen.be
and Waarneming.nl), and the number of sightings has been
increasing in recent years. There are also some recent
findings in both countries. Presumably the species (figure 12)
is not uncommon and still spreading.
Megastigmus strobilobius RATZEBURG, 1848
Material examined. BELGIUM (7 ♀♀, 4 ♂♂) • 7 ♀♀, 4 ♂♂,
Gilbuschheck & Côte des Forges, 1993, Belgium Forestry Office leg.,
coll. AR, reared ex Picea abies (ROQUES & SKRZYPCZYŃSKA, 2003). THE
NETHERLANDS (3 ♀♀) • 2 ♀♀, Brunssum – Treebeek, 50.562 – 5.566,
24.VI–1.VII. 2019, G. LOMMEN leg., coll. RMNH, light trap, S. ULENBERG
det.; 1 ♀, Tilburg – De Kaaistoep, 51.540 – 5.009, 13.VI.2020, P. VAN
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Figure 12. Habitus of Megastigmus spermotrophus (female). Coll. FV. Photo B. MINNEBO.
Map 16. Distribution of Megastigmus strobilobius.
Map M. ISSERTES (QSIG).
WIELINK leg., coll. TP, light trap, P. HOEKSTRA det.
Distribution (map 16). European, associated with several
conifers, especially spruces (ROQUES & SKRZYPCZYŃSKA, 2003).
Remarks. This species was reported once in the Netherlands
in several publications (SCHOEVERS, 1924; OUDEMANS, 1931;
GIJSWIJT, 1969). However, the species presence was rejected
at the beginning of the 21st century after checking all
available material (GIJSWIJT, 2003). Therefore, our publication
confirms or reaffirms the presence of the species.
Megastigmus suspectus BORRIES, 1895
Material examined. BELGIUM (1 ♀) • 1 ♀, Sint-Andries – Beisbroek,
51.171 – 3.160, 27.VI.2016, W. DEKONINCK et al. leg., coll. RBINS, yellow
pan trap, F. VERHEYDE det. THE NETHERLANDS (273 ♀♀, 17 ♂♂) • 1 ♀,
Putten – Schovenhorst (Arboretum), 16.V.1910, J. Th. OUDEMANS leg.,
coll. RMNH, GIJSWIJT 2003; 53 ♀♀, 1 ♂, Putten – Schovenhorst
(Arboretum), IV.1930, J. Th. OUDEMANS leg., coll. RMNH, reared ex
Abies cilicica […]; 1 ♂, Nunspeet, 9.IV.2003, T. SIMON THOMAS leg., coll.
RMNH, reared ex Abies sp.
Distribution (map 17). European, but a species originating
from southeastern Europe and Asia Minor. In the Netherlands,
two older reports are known from 1910 and 1931 (GIJSWIJT,
2003) and one recent report from 2003. In Belgium, it was
caught with a yellow pan trap in heathland. The species is
associated with Cedrus MILL. spp. and Abies MILL. spp.
Remarks. The older findings in the Netherlands, reviewed by
GIJSWIJT (2003), are coherent with its presence reported
throughout France (ROQUES & SKRZYPCZYŃSKA, 2003). This
species (figures 13–14) has been reared several times. Four
Abies spp. were reported as a host plant at least once: Abies
cephalonica LOUDON, A. cilicica (ANTOINE & KOTSCHY)
CARRIÈRE, A. firma SIEBOLD & ZUCC. and A. nordmanniana
(STEVEN) SPACH.
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Figure 13. Habitus of Megastigmus suspectus (female). Coll. RBINS. Photo B. MINNEBO.
Map 17. Distribution of Megastigmus suspectus.
Map M. ISSERTES (QSIG).
Figure 14. Frontal view of M. suspectus (female). Coll. RBINS.
Photo B. MINNEBO.

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DISCUSSION
This study cataloged sixteen species, of which only seven
were reported in Belgium, accounting for less than half of the
total. Notably, no species were identified in Belgium that had
not been previously reported in the Netherlands. We suspect
there is no actual reason why species occurring in the
Netherlands cannot be expected to occur in Belgium. With
92 specimens examined from Belgium, we reach only 8 to
9 % of the total amount of specimens studied. This highlights
a substantial observation bias, indicating the need for
broader sampling to obtain a more comprehensive
understanding of the species distribution.
Four European species are somewhat higher on the list of
species to be expected in Belgium: Bootanomyia stigmatizans
(associated with Quercus sp.); Megastigmus bipunctatus
(associated with Juniperus spp.), M. brevicaudis (associated
with Amelanchier and Sorbus sp.) and M. rosae (associated
with Rosa spp.). The remaining species are predominantly
non-native, often originating from the Nearctic region and
associated with conifers. These species tend to inhabit larger
coniferous forest patches, gardens, or arboreta, making their
presence dependent on finding the right host tree at the
appropriate time.
The identification of sixteen species in our study brings us to
the brink of the full spectrum of native and introduced
species in Western Europe, as outlined by ROQUES &
SKRZYPCZYŃSKA (2003). Some of the remaining species are
confined to host plants of the Mediterranean basin, facing
challenges in adapting to more northern climates, thereby
reducing the likelihood of their presence in our study area.
Two species perhaps have a chance. M. nigrovariegatus is a
non-native species we discussed in our paper in relation to
M. aculeatus and M. rosae. It is also associated with Rosa spp.
and occurs in France. A second plausible candidate is M.
pinsapinis HOFFMEYER, 1931. This species origins from North
Africa and/or Spain, but has been discovered up to north-
central France. It associated with Abies and Cedrus spp.
(ROQUES & SKRZYPCZYŃSKA, 2003).
Yet, as emphasized throughout our study, Megastigmidae
demonstrate a high sensitivity to introductions, creating a
dynamic where 'unusual' species from diverse regions can be
anticipated through importation. This underscores the need
for continued vigilance and monitoring in understanding
the intricate dynamics of Megastigmidae populations in
different ecological contexts.
ACKNOWLEDGEMENTS
The incentive to write this paper was based upon the interesting and still ongoing observations of Arp KRUITHOF and Jeanette ESSINK on
Megastigmus rosae in the Netherlands. They are very much thanked for communicating those observations and for being open to dialogue. Bart
MINNEBO further improved this paper enormously with his detailed photographs. Wouter DEKONINCK and Frederique BAKKER are thanked for their
help in accessing the collections (including scanning archives/documents) of RBINS (Belgium, Brussels) and Naturalis (Leiden, the Netherlands).
Els VAN GINKEL is thanked for providing us visual sources of OUDEMANS and Landgoed Schovenhorst. Koorosh MCCORMACK and Jean-Yves RASPLUS
are sincerely thanked for reviewing this paper and thereby giving us valuable feedback. We wish to also thank all observers who contributed to the
dataset used in the paper. Finally, Mehdi ISSERTES is thanked for making the layout and redrawing the maps in this item.

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