Relicts of East-Flemish inland dunes were investigated for the presence of dune-land fauna. Five of the 8 therevid species known from Flanders were found in the present study. In contrast to asilids, therevids showed to be pioneer species preferring areas with large bare sandy patches. Pit fall traps proved to be twice as effective to sample therevids than white or yellow pan traps. Yellow traps are ineffective. Highest activity and diversity is found in June and July

Bonte, D.

Dekoninck, W.

Grootaert, P.

Open Marine Archive

-- -- -- --------------------------------------------------------------------, 
BulletinS. R.B. c. K.B. V. E., 137 (2001) · 32-35 
Therevidae {Diptera) in the East-Fiemish inland dunes, 
pioneers on sandy soHs ? 
by Patrick 0ROOTAERT1, Wouter DEKONINCK1 & Dries BONTf2 
' Department of Entomology, Royal Belgian Institute ofNatural Sciences, Brussels. 
' Laboratory of Ecology, Zoogeography, State University Ghent. 
Summary 
Relicts of East-Flemish inland dunes were investigated for the presence of dune-land fauna. Five of 
the 8 therevid species known from Flanders were found in the present study. In contrast to asilids, 
thercvids showed to be pioneer species preferring areas with large bare sandy patches. Pit fall traps 
proved to be t wicc as effective to sample therevids than white or yellow pan traps. Yellow traps arc 
ineffective. Highest activity and diversity is found in June and July. 
Introduction 
The scope of the present study was to investi-
gate if there was still a characteristic dune fauna 
present in the relicts of the old inland dunes in 
the province of East-Flanders. In fact, in the past 
these poor agricultural lands were generally 
planted with woods or the sand was used for 
constructing or houses were built on the dryer 
elevated areas. So, very few original "dunes" are 
left. As to the origin of the sand and the dunes, 
we refer to DEKONINCK et al. (in press). 
Thercvid flies are often seen ''sunbasking" on 
bare sand patches in coastal dunes. Six species 
are known from the Flemish coast and this was 
the reason to pay attention to their presence in 
inland dunes. Another 2 species are reported 
from the rest of Flanders so that our fauna counts 
8 species. 
Therevids are related to Asilid Oies but they 
do not possess their strong snout. Instead they 
have large weak tabellae and it is supposed that 
they hold a prey between these thick lips and 
suck them out the way dolichopodid flies do. 
Unfortunately very little is known of their biolo-
gy (VAN DFR GOOT, 1985; OLDROYD, 1969). Ac-
32 
cording to VAN DER GOOT (Le.) Psilocephala arc 
"wood" species and their larvae are found in de-
caying wood. Dialineura species "fly" or forage 
on herbs growing on dry sandy soils. Van der 
Goot quotes further that Thereva species are ob-
served between the "leaves", whatever this 
means. 
There are no Red data lists nor distribution 
maps of therevids because there are too few ob-
servations to say something reasonable. In fact 
we start from nowhere. 
Material and methods 
Six sites with "dune" relicts in East-Flanders 
were sampled for their insect fauna. Table 1 
gives a survey of the stations per site and the 
grade of perturbation or management done at 
each station. 
From April until end September 1999, flies 
were collected with 5 pit fall traps and 3 white 
and 3 yellow pan traps per station (DEKONlNK et 
al. in press). To limit the variation in habitat and 
to ease comparison of the sites, the traps were 
places in dry areas, floristically dry heathland. 
Table I. Sites, localities and management per station. 
Station Locality 
Wetteren 
Uitbergen 
Site Area 
-------------+-----
Den Blakken Young heathland; recently cut pine - birch wood I (W) 
2 (U) 
3 (LV) 
4(LN) 
5 (MB) 
Kalkense Meersen Open duneland; recently cut pine- poplar wood j Lokeren Lokeren 
Mocrbekc 
Molsbergen Moss dunes (restored 5 year ago) 
Molsbergen ~dunes (restored 5 year ago) 
Heidebos I Open area in wood with heath; recently large Pru-
nus serotina was removed 
+-------------------6 (MW) Moerbeke 
·kc -r-:-7 (MA) Moerbc 
Steken 
Steken 
e 
e 
e 
e 
Steken 
Steken 
-
12 (SM) ens-St-Mrut 
Latcm 
-----L-
Observations 
Heidebos 
Ileidebos 
Stropersbos 
Stropersbos 
Stropersbos 
Stropcrsbos 
Golf course 
A total of 67 individuals, consisting of 60 fe-
males and 7 males, belonging to 5 species were 
found. Surprisingly most of the individuals were 
caught with the pit fall traps (Table 2). The co-
loured pan traps were less effective. The pit fall 
traps caught relatively almost twice as much as 
the white traps, the white traps double of the yel-
low traps. It is clear that yellow traps should not 
be used to catch therevids. The highest diversity 
and the largest numbers are caught in June and 
July (Table 3). 
rabic 3. Phenology of the species. 
r Species 
~ialineura ani/is 
Psilocephala ard 
Thereva bipuncta 
Thereva cmifera 
T11ereva nobilita 
Total number 
---
ea 
ta 
ta 
I 
May 
I 3 
3 
·-
Table 4 gives a survey of the species found per 
station and per site. Except for station MB and 
SB, therevids were found in all stations. The 
numbers of species and individuals are low 
making the results hard to interpret statistically. 
Neve1thelcss there arc some indications of the 
ecology of the species. Most individuals were 
found in the more recently perturbed areas which 
coincides with these sites with the largest open 
Open area in wood with heath 
----------------
rea with young heath; yearly mowed Large open a 
eagle fern 
Old meadow in wood grazed by rabbits 
Old meadow in wood, not so short grazed as SA 
Birch wood 
Open bares 
borderin-'g"-S_B _ ____________ -1 
pace; old birch wood cut in previous 
winter 
--Sand dune with heath, more than 90 years left un-
golfcourse disturbed in 
------------------~ 
Table 2. Preference of therevids for trap type (P: pit 
fall; W: white pan trap; Y: yellow pan trap). 
Species Trap Total 
p w y 
Dialineura ani/is 2 2 
Psilocepha/a ardea 2 6 2 10 
Thereva bipunctata 3 1 7 6 44 
Thereva cinifera 4 2 6 
Thereva nobilitata 5 5 
I Total 44 15 8 67 
Month I June I J uly A ug Sept Total 
r---
1 1 2 
2 I 7 1 10 
22 13 3 3 44 
6- ·~ 
4 l 
·----t 
5 
25 I 31 l 5 3 67 l 
sandy patches. The maximum number of 4 spe-
cies were found at a station in Heidebos where 
eagle fern, Pteridium aquilinum, was mowed 
every year, resulting in large open sandy patches 
w ith young Calluna. The largest number of spe-
cimens, all mainly Thereva bipunctata were 
found at the 2 stations at Lokeren. These two 
stations were 5 years before the sampling a was-
teland with rough vegetation and have been 
33 
cleaned up resulting in a large moss dune with a 
very short herb layer. Three species were also 
found in the freshly cut wood at Stropersbos, 
Table 4. Thercvid flies per site and station. 
I 
i 
c: c: Q) 5h c: 
'" 
Q) 
Q) 
'" '" :::; Q) Q) 
.D ..:.: Q) 
.... 0 ~ 5 ....l 
Species 
-
2 5 15 
1 2 3 I 
' 1 2 3 
Comments to the species 
Dialineura ani/is (L., 1761) 
A common inland species (Gent, Destelber-
gen, Mt:lle, Heusden, St. Amandsberg, Over-
mere, Diepenbeek, lloogstraten, Lanaken, Bil-
sen) with only a single record from the coast 
(Knokke). 
Only two specimens were found at Ilcidebos, 
Moerbekc. 
Psilocepllala ardea (F., 1794) 
A very common species in inland Flanders 
(Gent, Destelbergen, Mclle, Merelbcke, Heus-
den, Vinderhoute, St. Amandsbcrg, Munte, 
Heide (Antwerpcn), Audergem, Diepenbeek, 
Iloogstratcn, Lanklaar), but not reported yet from 
the coast nor South-Belgium. 
Our records do not indicate that this species is 
a woodland species {VAN DER GOOT, J 985) since 
it should be more abundant in the wooded areas 
at Heidebos, De Stropers and Wetteren. It is ins-
tead found in open areas. 
Tlzereva cinifera MEIGEN, 1830 
This species is very common at the coast and 
until now there '"'as only a single observation in 
indicating that there was an immediate explora-
tion of this new site by the therevids. 
Q) 6 Q) 
..:.: Q) ~ Q) 5 
.D ....l 
'" ~ Q) ~ 0 U'5 ::E U'5 
·-'--- -1 2 l I 
17 2 14 6 2 3 1 
3 1 4 2 1 
--
4 3 
--
1--
3 1 1 
---
.L !.... J 
inland Flanders (Heusden). 
Th. cinifera is dominant on the river dune at 
Uitbergen. Also two specimens were found in 
Lokeren. It probably follows the banks of the 
large rivers inland (Uitbergen near the Schelde 
and Molsbergen near the Durme). Both sites 
have recently been perturbed thoroughly and 
have large patches of bare sand. 
Tlrereva bipunctata MEIGEN, 1820 
This species is uncommon in Belgium. Only 9 
specimens were present in the collection of the 
RBINS: Knokkc, De Panne, Turnhout and Zu-
tendaal. No records are available from the area 
around Ghent although it was thoroughly investi-
gated by GOETGHEBUER and BEQUAERT. 
In the present study, it is the dominant species. 
Especially in Lokeren and the station with the 
yearly mowed eagle fern at Hcidebos. Th. bi-
punctala is probably a pioneer species in areas 
with large bare sandy patches. 
Thereva nobi/itata (F., 1775) 
Th. nobilitata is a common species with a 
large distribution. It is found at the coast as well 
in the rest of the country. In the present study it 
is not abundant at all. 
n 
V 
SI 
1 
It 
p 
c: 
ol 
E 
pl 
h; 
se: 
th 
n< 
fr 
re 
w 
S• 
Tltereva annul"ta (F., 1805) 
A very common species at the coast with 2 
records inland (Hcusden, Kalmtbout). This ob-
vious species was not observed in the present 
study. 
Therevafulva (MEIGEN, 1804) 
A not very common species known from the 
coast, the area around Ghcnt and the "Kempen". 
It was not observed in the present study. 
Psilocephala rustica (PANZER, 1803) 
A very rare species only known from Munte 
(23.Vll.l936, det. VAN DER GOOT). It was not 
observed in the present study. 
Conclusions 
Of the 8 species that are supposed to occur in 
East-Flanders, we observed 5 species during the 
present study. Species commonly caught with 
hand captures were quite rare here and vice ver-
sa. So, more records are needed to understand 
the distribution patterns of the species: coastal, 
non-coastal, following the rivers inland, species 
from wood land etc. 
To make an assessment of the presence ofthe-
revids, pit fall traps arc twice as effective as 
white traps, yellow traps are the least effective. 
Sampling should be done at least during June 
and July since the greatest activity and diversity 
occurs during that period. 
In the present study we conclude that therevids 
can be considered as pioneer species. They ap-
pear quickly in freshly "restored" areas where i.e. 
the shrubs and trees have been removed (Uitber-
gen, Molsbergen, MA at Moerbeke) resulting in 
large bare sandy patches. 
Much more studies are needed to understand 
the role that the therevids play in the ecology of 
sandy habitats. 
Acknowledgements 
The present study was done by order of the Fle-
mish Government, AMINAL, Afdeling Natuur Oost-
VIaanderen (AMINAL/NA/98). The authors thank 
Mrs Viviane V ANDEN BLL and her staff for their en-
thusiastic support to the project. 
References 
DEKONINCK W., BONTE D. & GROOTAERT P., 2000.-
Onderzoek naar herstelmogelijkheden t.b.v. het 
behoud van de specifieke entomofauna van de 
landduinen in Oost-Vlaanderen. Eindrapport de-
cember 2000: 211 pp. met bijlagen 44 pp. · 
OLDROYD H.1969- Diptera Brachycera section (a) 
Tabanoidea and Asiloidea. Handbooks for the 
identification of British Insects. IX. 4. 132 pp. 
VAN DER GOOT V.S., 1985.- De Snavelvliegen (Rha-
gionidae), Roofvliegen (Asilidae) en aanverwante 
families van Noordwest Europa. Wetenschappe-
lijke mededelingen K.N.N. V. 171, 66 pp. 
35 


Therevidae (Diptera) in the East-Flemish inland dunes, pioneers on sandy soils?

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