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Dipterists Digest 2020 27, 61-82
The identity of Syntormon pseudospicatum Strobl
(Diptera, Dolichopodidae)
C. MARTIN DRAKE
Orchid House, Burridge, Axminster, Devon, EX13 7DF, UK; martindrake2@gmail.com
Summary
Syntormon pseudospicatum Strobl has been regarded as either a valid species or a synonym of S. pallipes Fabricius,
representing one end of the spectrum of variability in colour and hairiness of the hind leg. It is shown here that the
variation in measured characters was discontinuous and that the two species are clearly distinct using morphometric
analysis. Syntormon pseudospicatum in Britain, and perhaps throughout its range, is almost confined to brackish
sites. The strong evidence from structure and habitat suggest that S. pseudospicatum is a good species. Strobl’s type
specimen is re-described. A key to distinguish males is given.
Introduction
Species of Syntormon are small dark green or yellow-marked sympycnines found in a variety of
wetlands. World-wide about 110 species have been described, of which 41 are known in the West
Palaearctic and 15 from Britain (Chandler 1998, Grichanov 2013). The male secondary sexual
characters (MSSC) provide external features that are useful in most cases in their identification
without resorting to examination of the tiny hypopygium. MSSC are expressed in elongate
antennae and in a wide range of modifications in leg chaetotaxy, and often most conspicuously
in the shape of the hind basitarsus and its setae. Despite the obvious nature of these MSSCs, the
validity of S. pseudospicatum Strobl, 1899, remains contentious: is it a synonym of S. pallipes
(Fabricius, 1794) or a valid species? Grichanov (2013), Chursina and Grichanov (2019) and
Maslova et al. (2019) regarded S. pseudospicatum as a synonym but Negrobov (1971, 1975),
Pollet (2011) and Persson et al. (2019) retained its species status.
Syntormon pallipes is a common Palaearctic species and the first in the currently
recognised genus to be described. Loew (1850) regarded it as a very variable species. He
described three varieties but was reluctant to raise them to the rank of species since they seemed
to form a continuum from those with entirely pale hind femora, tibiae and base of the basitarsi,
and whose tibiae and basitarsi had sparser, shorter setae, to those with dark apical rings on the
hind femora and tibiae, entirely black tarsi, and denser, longer setae on the tibiae and basitarsi; he
divided the darker types into two varieties. Species were later described that match Loew’s pale
variety, including S. pseudospicatum and S. uncitarsis Becker, 1902. Becker (1918) later decided
that these two pale species were merely pale forms of S. pallipes. Indeed, there is nothing in
Strobl’s (1899) description of S. pseudospicatum that differs from Loew’s more detailed
description made half a century earlier, with the exception of the face character that Becker (1918)
ascertained, on examining the type specimen, was an artefact due to shrinkage. Once this
apparently conspicuous difference from S. pallipes is removed, Strobl’s (1899) description then
has only two convincing characters that differentiate his species from S. pallipes: all the femora
and tibiae are entirely yellow, and the hind basitarsus is black only in the apical half. Becker
(1918) made the observation (my translation) “As an additional difference, Strobl could have
mentioned that the hind tibiae were scantily or only shortly ciliated.” Parent (1938) agreed with
Becker’s conclusion but did not include the paler leg colour in his description of S. pallipes
(despite the fact that he treated S. pseudospicatum as synonym of S. pallipes), whereas Lundbeck
(1912), who appears to have been unaware of S. pseudospicatum as he did not give it as a synonym
of S. pallipes, gave an accurate description of the colour variation.
62
Negrobov’s (1975) key separates the species as follows:
- First segment of hind tarsi with two hooks merged practically to the apex. Hind
tibia with a row of dense bristles on the outside. Hind tibia apically and hind tarsi
basally dark ……………………………………………………………….. pallipes
- First segment of hind tarsi with two hooks separated practically to the base. Hind
tibiae with sparser bristles. Hind tibiae apically and hind tarsi basally yellow
……………………………………………………………………. pseudospicatum
Maslova et al. (2019) and Chursina and Grichanov (2019) examined about 140-150
specimens from widely separated locations in the Palaearctic, and which probably included some
in common to both studies. Maslova et al. (2019) concluded that the characters used by Negrobov
(1971) were too variable to allow the two species to be distinguished and, in one series of
specimens, there were transitional forms in which the characters overlapped. Chursina and
Grichanov (2019) used morphometric and genetic analysis (see Discussion). Like Loew and
Becker, both sets of workers concluded that all the specimens were S. pallipes, making S.
pseudospicatum a junior synonym. I and my colleague Roy Crossley had also examined many
specimens, mainly from Britain. Using Negrobov’s key, pale British specimens of pallipes could
be identified as S. pseudospicatum, but not satisfactorily since none showed consistent differences
in the separation of the hooks on the hind basitarsus, as illustrated by Negrobov (1971).
Syntormon pseudospicatum was added to the British list on the advice of C.E. Dyte (Chandler
1998) but possibly on a misunderstanding of its true identity.
The existence of paler and darker forms is uncontested, but whether they represent distinct
species cannot be resolved by merely examining the type specimens since several eminent
dipterists have already done this. Instead, the issue appears to be whether the variation is
continuous, as would be expected in a highly variable species, or shows a discontinuity
corresponding to the two taxonomic entities. In this paper, I first establish the nature of the
variation using a principal component analysis, then identify characters that most reliably separate
the species using a discriminant analysis. I also redescribe Strobl’s type specimen of S.
pseudospicatum. Distribution and habitat information from the British national recording scheme
that includes dolichopodids is used to show preferences of the two taxa.
Methods
Measurements or counts of 29 characters were made in 157 British specimens collected from
widely separated areas, and 21 specimens from France, Greece, Portugal and Spain, including
Strobl’s holotype of S. pseudospicatum (Table 1, Fig. 1). The features selected were those already
known to be variable, along with more detailed measurements of the hind tarsus and antenna
which show important taxonomic MSSCs in the genus. Measurements were made at x90
magnification to the nearest unit of an eye-piece graticule or to half a unit for characters smaller
than 12 units (1 unit = 0.0155 mm). The angle between the hook on the hind basitarsus and the
segment’s shaft was measured by fixing a protractor to the eye-tube of the microscope and a
pointer to the eye-piece, and lining up a squared graticule in the eye-piece with the axes of the
hook and tarsus. Although the measurements could be made with precision to 1 degree, the
curvature of the front edge of the column with hooks and basitarsus shaft introduced some error.
Principal component analysis (PCA) was carried out on a correlation matrix. To avoid a
possible complication of allometry, lengths were first standardised by dividing by the longest
measured character (hind tibia) as this was the most accurately measured feature. This was
thought to be a better procedure than using the residuals of the regression of each character with
63
the tibia since the regression would be based on both taxa, thus introducing bias and dependence
on the specimens used in the dataset (Rae 2002). The resulting size-standardised variables were
then almost or completely uncorrelated with the tibia length. Several characters deviated from
normality using a Shapiro-Wilk test, in particular the width of the rings on each of the three hind-
leg segments were clearly bimodal, so no transformation could normalise these data. When each
species was treated separately, each character had an almost or completely normal distribution,
so combining them into a bimodally distributed dataset was an unavoidable source of error.
Transformations applied to all characters using logs (ln x+1) or arc-sine (since the size-
standardised values were proportions) made no useful difference, sometimes being either
marginally better or worse for different characters, so none was applied. Rare outliers were one
reason for deviation from normality but these were genuine values when checked so there was no
reason to remove or replace them with an average value. A few mainly trivial variables were
excluded, but also Tibia_ring (see Table 1) which was very closely cross-correlated with
Femora_ring, leaving 20 characters.
Once it had been established using PCA that there were two distinct groups, specimens
were allocated to either S. pseudospicatum or S. pallipes. Discriminant analysis was used to
identify characters that best separated the species. Instead of using the size-standardised raw data,
a new set of variables was constructed using ratios of lengths that better described some aspect of
shape, for instance the ratio of the length of the dark ring on the femur to the total femur length.
These characters, along with counts and the hook angle, are given in Table 2. It was expected
that these ratios would be of better use when constructing an identification key than the less easily
usable lengths of the raw data. An alternative procedure to this subjective choice of derived
characters would have been to use the vast number of all possible ratios and counts, which would
have been unwieldy and time-consuming to analyse. Tergite colour was omitted as it was
measured as a nominal variable whose inclusion would violate one of the many assumptions of
discriminant analysis (Zuur et al. 2007). As with the original measurements, some were not
normally distributed within each species, but as no transformation consistently improved the
distributions, none was applied. Successive runs of the analysis were made, dropping the variable
with the lowest discriminant coefficient until a small number of useful variables remained that
still achieved high separation of the species. Differences between mean values of each variable
were tested after checking for non-significance in the variance ratio of each pair of characters.
Both PCA and discriminant analysis were undertaken using Community Analysis Package 4
(Pisces Conservation 2007). Excel with the Analyse-it add-in was used for all other analysis.
Information on British distribution and habitat affinity was obtained from my own
collecting and from data sent to me in my capacity as organiser for dolichopodids in the national
recording scheme for empidids, hybotids and dolichopodids (Dipterists Forum 2019). The data
are held privately and are not currently publicly available. Dates of records of S. pseudospicatum
are 1904-1969 for 32 specimens in the Natural History Museum, London, and 1971-2018 for 68
records from several competent recorders. Syntormon pallipes records cover the period 1876 to
2018 and are impossible to disentangle from S. pseudospicatum.
I have used the neuter gender for the species names, as argued by Drake and Welter-
Schultes (in press). There it is shown that a series of mistakes by Loew (1857) precluded the
name of his new genus being masculine, contrary to his intention.
64
Fig. 1. Measurements taken on the hind leg and antennae of Syntormon pallipes and S.
pseudospicatum. The numbers cross-refer to Table 1. Black line: lengths; blue lines: counts
between arrows; red lines: angle subtended: (a) hind leg; (b) hind tarsus 1
st
and 2
nd
segments; (c) hind tibia, dorsal face; (d) antenna, inner face.
65
Table 1. Syntormon pallipes and S. pseudospicatum features measured in 178 specimens,
and 20 characters (with their labels) used in principal component analysis. The positions of
most measurements are shown in Fig. 1. Parts of legs always refer to the hind leg.
Anatomical
feature
Number
Measurement Label for PCA
Femur 1 length to trochanter on dorsal edge Femora_L
2 length of dark ring on mid-line of anterior face
Femora_ring
Tibia 3 length
4 length of dark ring on mid-line of anterior face
5 diameter at 1st antero-dorsal seta Tibia_W
Tibial fringe 6 number of hairs from 1st antero-dorsal seta to
tip, ignoring the apical seta
7 number of hairs proximal to 1st ad seta
[all these hairs in 6 and 7] Fringe_N
8 length of hair at basal ¼ point of tibia
9 length of hair at midpoint of tibia
10 length of hair at apical ¾ point of tibia
[average of these three lengths, 8, 9 and 10] Fringe_L
11 diameter of hair next to last antero-dorsal seta
relative to this seta (estimate)
Fringe_rel-diam
12 subapical subsidiary hair row, total number of
hairs, ignoring apical seta
Subfringe_N
13 subapical subsidiary row, number of hairs as
large as those in anterior fringe
Subfringe_big_N
Basitarsus 14 length Metatarsus_L
15 length of black ring on centre-line of anterior
face Metatarsus_ring
16 diameter at narrowest, near mid-point Metatarsus_W
Basitarsus hook 17 shape: curved or upright (inconsistent)
18 height Hook_H
19 length from hook’s inner face to upright setula
on antero-ventral face of shaft
Hook-to-Hair
20 angle of hook’s main axis with main axis of
tarsus shaft
21 angle of hook’s proximal edge with main axis
of tarsus shaft
Hook_angle
Tarsus 2
nd
22 length Tarsus2_L
segment 23 diameter Tarsus2_W
24 diameter including ventral pubescence
Antenna 25 postpedicel length Antenna_L
26 postpedicel width Antenna_W
27 arista length Arista_L
Tergite 28 yellow patch present on 2
nd
tergite
29 yellow patch present on 3
rd
tergite
Thorax 30 length including scutellum, dorsal view Thorax_L
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Table 2. Characters used in discriminant analysis. The numbers in the equations refer to
the numbered characters in Table 1 and Fig. 1.
Code Equation
Femora_ring 2÷1
Tibia_ring 4÷3
Tarsus_ring 15÷14
Tibia_thickness 5÷3
Tarsus_D1:D2 16÷23
Tarsus_L1:L2 14÷22
Hook_H:hair 18÷19
Fringe_N 6+7
Fringe_L average of 8, 9, 10
Fringe_tibia_ratio (average of 8, 9, 10) ÷ 5
Fringe_diam 11
Fringe_subrow_N 12
Fringe_subrow_big 13
Tergite_colour 28
Anten_L:arista 25÷27
Anten_L:H 25÷26
Hook_H:shaft 18÷16
Hook_angle 21
Results
Morphometrics
The PCA plot of the first two axes showed two distinct clusters with almost no overlap and no
indication of continuous variation from one to the other (Fig. 2). These two clusters corresponded
well with the species regarded as S. pseudospicatum on the left and S. pallipes on the right. The
first axis explained 34% of the variance in the sample, with a high eigenvalue (6.80), and the
second axis explained a further 15% of the variance but with a relatively small but still important
eigenvalue (2.92). The next two axes explained relatively little of the remaining variation despite
having eigenvalues greater than 1.0; cumulatively all four axes still explained only 60% of the
total variation (axis 3: eigenvalue 1.31, 6.5% of total variation; axis 4: eigenvalue 1.07, 5.4%).
Points for the two taxa overlapped almost completely when the second and third axes were plotted
(not shown), suggesting that higher axes would reveal no further insight. Eigenvectors having
the greatest influence were those orthogonal to the diagonal axis that separates the two species:
the number of hairs in the main and subsidiary tibial fringes (Fringe_N, Subfringe _N) which
were greater in the direction of S. pseudospicatum, and, in the opposite direction towards S.
pallipes, greater values for the average length of hairs in this fringe (Fringe_L), the relative
thickness of these fringe hairs compared with the antero-dorsal seta (Fringe_rel-diam), the
number of large hairs in the subsidiary row (Subfringe_big_N), the width of the dark rings of the
femora and basitarsus (Femora_ring, Metatarsus_ring), and the angle of the shaft of the hook
(Hook_angle). Characters that did not help in describing the separation of the species were
indicated by vectors lying approximately in the direction of the diagonal axis between them; these
were several characters relating to the antennae and lengths of leg segments.
Specimens of both species from Britain and continental Europe are indistinguishable on
the PCA plot, despite their wide geographic separation and different climates where they
developed (from Kefalonia in Greece to northern Scotland). Strobl’s type specimen from Spain
67
is at the fringe of the S. pseudospicatum cluster but clearly related to British and French
specimens.
Fig. 2. Principal component analysis of Syntormon pallipes and S. pseudospicatum
measurements. Upper graph shows the distribution of scores along the first two axes,
distinguishing British (GB) and non-British (non-GB) specimens, and indicating Strobl’s
type specimen. Lower graph shows the vectors for all 20 variables.
68
Fig. 3. Axis 1 score of PCA plotted against latitude (above) and date of collection, expressed
as day number of the year (below) for Syntormon pseudospicatum (open circles) and S.
pallipes (black circles).
69
To identify two groups for discriminant analysis, the specimens were allocated using their
position in the PCA plot. Clearly some guesswork was needed for points on the touching
boundaries of the clusters. The ratio of the dark ring on the hind tibia (present in S. pallipes,
absent in S. pseudospicatum) was strongly correlated with the femora ring (r
2
= 0.93) so was
excluded to satisfy an assumption of the method. In the step-wise removal of the least influential
character, all but the three characters with highest discriminant function coefficients could be
removed before any specimen was incorrectly identified. These three variables were the ratio of
the black rings to total lengths of the femur and basitarsus, and the average length of the hairs on
the tibial fringe. The eigenvalue had dropped from 13.98 with all 16 variables to 9.18 with just
the three final variables, and the test statistics (chi-squared of the canonical correlation, Wilk’s
lambda) remaining highly significant at each step. Two other variables that were removed late in
the procedure were the ratio of the basitarsus to second tarsal segment and the relative thickness
of the fringe hairs to the adjacent antero-dorsal seta at the distal quarter of the tibia. The first of
these was a statistical artefact resulting from genuine outliers that produced non-normality in the
data for this variable. The second variable for relative thickness of the hairs was clearly of some
additional value in distinguishing the species.
Separate PCA ordinations for each species showed a diffuse cluster for each, with no
distinct groupings within the cluster on a plot of the first two axes (not presented here). The first
axis in both ordinations explained only 19-20% of the variance, suggesting there were only weak
gradients within the data. In S. pseudospicatum, the gradient was dominated by the width and
number of hairs in the fringe. In S. pallipes these gradients were dominated by a wider ring on
the hind femur, robust hind tibia and a wider fringe, but the number of hairs in the fringe was
unimportant. Thus the two species appear to show only partial similarity in the main areas of
variation. The large variability in leg colour in S. pallipes, ranging from the more usual narrow
apical ring to entirely black, may correspond to Loew’s (1850) second and third varieties.
Mean values of each variable were calculated using untransformed values of the size-
standardised lengths. Values are not presented as lengths and ratios have little practical use. Tests
for the differences between the mean values of the two species were significant for most variables,
with some doubt about the validity of a t-test for a few variables where the variance ratio was
significant (that is, the variances were not similar). These included the bimodally distributed
variables relating to the black rings on the femur and tibia, and the yellow basal ring on the
basitarsus, and three other variables where genuine outliers led to non-normality in the data. Non-
significant differences in means mainly related to the thorax length and antennae, although not
postpedicel length which was minutely but significantly shorter in S. pseudospicatum (p<0.05).
The bulk of the characters relating to the legs were therefore the most important source of the
differences between the species. Absolute lengths for the hind tibia and thorax, taken as two
values likely to represent total size, were almost identical, even though those for S.
pseudospicatum were significantly greater (p<0.05).
The axis 1 score of the PCA may be taken as a surrogate for the shape of specimens, and
which can be correlated with external factors that may influence it. Time of year and latitude
were tested. Time of year (as day number) was restricted to British and French specimens to
avoid early or unknown dates for Portugal, Spain and Greece. There was a weak decline in axis
1 score through the year for both species (r
2
=0.137 for S. pallipes, 0.296 for S. pseudospicatum)
(Fig. 3). The parallel motion of the change in the score suggests that the two species remain
distinctly separate all through the year. Latitude for all specimens showed no relationship (Fig.
3).
Colour pattern in some dolichopodids shows a seasonal change. If some of the variation
in S. pallipes and S. pseudospicatum can be shown to correlate with season, it would reinforce
the contention that they are separate species. Two characters were examined: the colour of
70
tergites 2 and 3 (either all green or with large yellow lateral marks) in both species, and the length
of the black ring on the hind femur of S. pallipes (S. pseudospicatum has no femoral ring so cannot
be tested). In both species the tergite colour showed a pronounced seasonal change in frequency:
entirely green tergites predominated in early-flying specimens and those with yellow patches
predominated later in the year (Fig. 4). The same trend has been seen in a Belgian population
(Marc Pollet pers. comm.). The length of the black ring in S. pallipes also showed a weak
correlation with time of year (r
2
= 0.18) but the slope was highly significantly different from zero
(p<0.0001), which suggested that some aspect of season influenced the pattern, from a wider ring
in spring to a narrower one in late summer (Fig. 5).
Fig. 4. Number of specimens with entirely green tergites (green bars on histograms) or with
yellow patches on tergites 2 and 3 (yellow bars) of British and French specimens of
Syntormon pseudospicatum and S. pallipes in blocks of 25 days through the year.
Fig. 5. Ratio of the length of the black ring to total length of the hind femur plotted against
date of capture (day of year) for 112 specimens of Syntormon pallipes.
71
Fig. 6. Distribution of Syntormon pseudospicatum and S. pallipes in Britain.
Habitat
A further important external factor differentiating these species was habitat preference. The
British distribution of pseudospicatum is almost exclusively coastal (Fig. 6), and it has been found
on brackish sites, mainly saltmarsh and rarely at seepages on coastal cliffs. Only rarely has
pseudospicatum been found at inland freshwater sites, and then only a few kilometres from the
coast, which suggests that they may have been strays. My French specimens were also from
saltmarsh, and Strobl’s type specimens was collected from Algeciras on the Spanish coast. Pollet
and Meuffels (2016) stated that S. pseudospicatum has a clear preference for mud and saltmarsh
in The Netherlands where it can be numerous. Syntormon pallipes is widespread and eurytopic,
occurring at both freshwater and brackish sites. Both species have been collected at the same
brackish sites on the same day on several occasions, while only a short distance inland away from
saline influence only S. pallipes was found. Lundbeck (1912) also found both together although
he did not use the name S. pseudospicatum for his paler form. A full analysis of the British
distribution of the two species is not currently possible with the data in the national recording
scheme as many coastal records of S. pallipes probably include S. pseudospicatum (Dipterists
Forum 2019). This may apply particularly to the Scottish coastal records; for example, both
72
species were recorded by Plant (1995) from the tiny island of Sule Skerry north of the Scottish
mainland.
Re-description of Syntormon pseudospicatum holotype
I provide a re-description of the holotype of Strobl’s S. pseudospicatum, kindly given in loan by
the Naturhistorisches Museum, Vienna, Austria. The male specimen is in very good condition,
lacking only the left antenna, the tip of the right arista, and the one of the two claws of the right
hind basitarsus. Characters that were missing or obscured have been substituted by the condition
found in British specimens and indicated in square brackets.
There are two labels on the staging pin. The upper is Strobl’s original white handwritten label:
Synt. pseudo-
spicatum
m. Algiciras ? [the isolated last character, indicated here by “?”, is illegible]
Strobl.
The lower label is a red typed label:
HOLOTYPUS
Redescription. Male. Body length 3.1mm, wing length 3.4mm measured from base, 3.0mm
measured from vein h. Head. Frons glossy metallic purple-blue, faintly microtomentose, shining
either side of ocellar triangle; width at front ocellus about 2.5 times as long as distance from hind
ocellus to anterior ridge above antennae. Face tapered from below antennae to mouth edge but
strongly shrunken in the type specimen [in undistorted specimens, parallel in lower half, its
narrowest width half its width under antennae]; silver-dusted [slightly golden just below
antennae]; black ground colour. Ocellus raised above level of flat upper frons. Occiput metallic
green but dulled by white dust, ground colour scarcely visible in lateral view. Eyes finely hairy;
lower facets about twice diameter of upper facets. Palps small, triangular, black with silver
dusting and inconspicuous fine short white hairs; proboscis small, dark brown, with hairs about
equal to its depth. Antennae black; scape bare with apical inwardly directed conical projection,
its apical width equal to segment length; pedicel with coronet of apical short setae and long conus
twice as long as basal width of segment; postpedicel long, parallel-sided in basal half, tapering in
apical half to pointed tip; entirely covered with short curled pale hairs; arista inserted dorsally just
behind tip of postpedicel, finely pubescent; ratio of scape: pedicel: postpedicel: arista – 11: 15.5:
40: 19+ (arista broken, only one present). Chaetotaxy typical for the genus: 2 long ocellars, 2
long upper orbitals, 2 very short postocellars, their length equal to ocellar triangle length,
postoculars black in upper third (8 setae including 2 set back from marginal row at vertex), white
in lower two thirds (13 setae), about 9 long white setae on lower occiput mediad of
postocular
row. Thorax. Metallic green except meron which is almost black above mid and hind coxae,
and metepimeron which is green-tinged but nearly black; dorsum sub-shining and thinly pale
grey-dusted, but less dusted and darker copper-coloured along lines of ac and dc setae and at most
seta insertion points; pleura ground colour mainly obscured by grey-white dust; scutellum more
shiny on smooth central half, granular and coppery on lateral quarters; dorsum flat in front of
scutellum in area bordered by last two dc and end of ac row; ac biserial in front (first 3 pairs),
then uniserial (8 setae) but with setae pointing alternately left and right, row ending between 4
th
and 5
th
dc setae, fairly long, about ⅓ length of adjacent dc and about equal to distance between
ac and dc rows; dc ‒ 2 pre- and 4 post-suturals, 5
th
inset, 1-5 similar in size, the 4
th
the shortest,
the 6
th
longest (about 1.3 x length of 5
th
); intra-alar ‒ 1 pre- and 2 post-suturals in almost straight
line; 1 strong posterior supra-alar; 1 moderately strong anterior supra-alar; anterior slope of
dorsum with about 7 fine short black setae in front of dc, 3 longer black outside dc; 2 notopleurals,
anterior stronger and almost on lower suture; 1 strong upper and 1 weak lower postpronotal; about
73
5 fine short white lower and about 11 fine white upper proepisternals; 3 (?4) short black pronotals
either side; 3 fine white katepisternal hairs just in front of posterior spiracle; vertical row [5-6] of
metepimeron hairs [equally spaced on posterior corner; only 3 visible in type], [single fine white
setae at top and bottom of outer face, not visible in type]; scutellum with 2 long strong lateral, 2
very short fine ‘apical’ hairs and similar hair on side in front of lateral seta. Legs. All pale yellow
of similar hue but black, although greyed by thin dust, on basal ⅔ of mid and most of hind coxae
(yellow-tipped), outer basal corner of front coxa, tarsomeres 4+5 of front leg, 2-5 of mid and hind
legs, and apical ½ of hind basitarsus; grading yellow to black on segments where colour changes.
Chaetotaxy of legs: Front leg (I): coxa I – all hairs and apical setae yellowish white; femur I –
short pre-apical pv scarcely longer than vestiture hairs; no ventral vestiture; tibia I – very short
pd at apical quarter, its length about 1.5 times vestiture which is rather short and in regular rows,
minute apicals; anterior apical comb well developed; tarsal I segments unmodified. Mid leg (II):
coxa II – apical and outer anterior setae black, hairs white, inner apical setae white; trochanter II
with 2 black ad setae [usually only 1]; femur II – black preapical anterior, posterior and pv just
distal to anterior, ventral vestiture of fine pale hairs along most of length; tibia II – ad at paired
with pd, at ⅓, just beyond ½, small pd at ¾, weak ventral at ½; apicals ad, pd, av all strong,
remaining apicals weak; tarsomeres II unmodified. Hind leg (III): coxa III – 1 strong black outer
seta at basal ¼, a few tiny white hairs on upper and lower parts of outer face, and slightly stronger
white hair below main seta; trochanter III – 1 black ad; femur III – black pre-apical pv, anterior
and stronger av twice length of anterior; depth of femur 1.5 times maximum depth of mid and
fore femora; tibia III – 4 ad and 4 pd more or less equally spaced but not paired except for the
most distal setae; 2 av at apical ¼; 2 pv at apical ¼; anterior row on entire length of rather weak
setae only slightly (about 1.2 times) longer than shaft width; posterior vestiture slightly denser in
apical ; small posterior apical comb; width of shaft marginally greater than mid tibia; tarsus III
– basitarsus with ventral column at its base with bifid claws curving distally; 1 small nearly
upright setae in mid ventral position; vestiture slightly longer in basal anterior cluster; remaining
tarsomeres
unmodified. Claws on all legs short, pulvilli reaching about ¾ claw length, empodium
distinct. Length ratios of femur, tibia, tarsomeres 1-5 (relative to tarsomere 5 expressed as 1.0)
in front leg 6.9/6.8/4.4/1.9/1.4/1.1/1, mid leg: 7.8/8.4/4.4/2.1/1.4/0.9/1, hind leg
7.9/10.4/2.6/2.6/1.6/1.1/1. Wings. Entirely hyaline, slightly grey-tinged, equally shaded all over;
veins dark but costa and bases paler, yellow at extreme base proximal to vein h; venation typical
of Syntormon; microtrichia even over all cells except extreme base of cells at root of wing where
microtrichia are minute and sparse; calypter yellow with narrow slightly darkened margin where
hairs arise, hairs yellow; [halter yellow with base of stem brown – missing (right-hand) or entirely
obscured (left-hand) on type]. Abdomen. All tergites metallic green, shining but thinly dusted;
T2 and T3 with yellow lateral patches extending full width of lateral margin and narrowing
dorsally, on T2 nearly reaching the midline, more widely separated on T3; all setae and vestiture
black dorsally but 2 white marginal setae on T1 on lower edge, white hairs on T1 laterally and
anterior two ranks dorsally, white vestiture along lower margin of all tergites; dorsal vestiture of
T2–T4 in 5-6 ranks; longest marginal setae about half tergite length; hypopygial capsule black;
sternite 1 dark, 2, 3 and anterior corners of 4 yellow, 5 dark; sternite hairs white.
Discussion
When I started this study, I tended to agree with the opinion of several eminent dolichopodid
workers that S. pseudospicatum is merely a variety of S. pallipes. It was therefore somewhat
surprising that the morphometric analysis and habitat specificity indicate that they are almost
certainly different. A key result is that the variation that so many previous authors persuaded
themselves was gradual is actually discontinuous. Furthermore, there are small differences in the
basitarsus shape that, along with the well-established leg colour and chaetotaxy, contribute to the
74
separation of these two species. Not only are there strong morphological grounds for keeping the
species separate but S. pseudospicatum has a narrow habitat range compared to that of S. pallipes,
the former species being almost restricted to saltmarshes and other brackish sites in northern
Europe where it may live alongside S. pallipes.
Criticism may be levelled at the use of untransformed ratios in both PCA and discriminant
analysis, particularly as some of the most influential characters had bimodal distributions which
cannot be normalised. Hills (1978) recommended using the logarithm of ratios but this did not
appear to markedly affect the present results.
Fig. 7. Genitalia and cerci of Syntormon pseudospicatum and S. pallipes: (a) whole capsule
in ventral view of pseudospicatum; (b) cerci of pseudospicatum (two examples); (c) cerci of
pallipes; (d) cerci of pallipes (another specimen) showing setae and the basal membrane
connecting the cerci to the capsule.
Since first submitting this paper for publication, Maslova et al. (2019) and Chursina and
Grichanov (2019) published their papers on S. pallipes and S. pseudospicatum, and concluded
that they were one variable species, S. pallipes. Maslova et al. (2019) illustrated the genitalia of
both species and enumerated differences that they detected although, as they regarded
pseudospicatum as a synonym of S. pallipes, they interpreted these differences as part of the
variation within S. pallipes. Some of the described features appear due to the angle of view,
particularly the length of the terminal section of the phallus, but also several differences in the
75
cerci that they illustrated in dorsal view. I have illustrated the genitalia of S. pseudospicatum in
ventral view (Fig. 7) which is identical to the figure of S. pallipes in Maslova et al., indicating
that their figure of S. pseudospicatum with a rounded hypandrium is probably an artefact of the
preparation. Two examples of the cerci of each species (Fig. 7) show slight variation but are
effectively indistinguishable, and this suggests that the variation described by Maslova et al.
(2019) is trivial (and their figures also inaccurately show the cerci as a single plate although it is
two separate articulated appendages). My own conclusion is that the genitalia are
indistinguishable (see also Drake in preparation). However, genitalia may not be the final arbiter
in distinguishing species, particularly as the clearly distinct species Syntormon monile Haliday in
Walker and S. silvianum Pârvu have very similar genitalia, and differences between the genitalia
of several British Syntormon are trivial compared to conspicuous differences in their legs and
antennae.
Chursina and Grichanov (2019) present a different issue. The chance must be vanishingly
small of two studies being undertaken independently and concurrently on the same pair of species
using morphometric analysis, and coming to the opposite conclusion. This has happened with S.
pallipes and S. pseudospicatum. Chursina and Grichanov (2019) analysed one leg colour
character, geometric morphometry of wing size and shape, and molecular sequences of COI and
12S rRNA. I cannot fault the work except for two points. The photograph of the hind leg of the
taxon they call S. pseudospicatum does not resemble Strobl’s type or any of the specimens I used
in my analysis; in particular, the basitarsus is narrow and almost cylindrical, and the basal column
with its terminal hooks lies at a shallow angle to the shaft, with the hooks apparently being almost
undeveloped. Secondly, they identified specimens using Negrobov’s (1975) key, in which the
first character mentioned is the degree of division of the two hooks on the hind basitarsus, but I
cannot see this difference between the specimens I have examined. Whatever the reasons for our
different conclusions, they must explain both sets of results which cannot be dismissed since they
are well supported by statistical analysis. In brief, Maslova and Grichanov (2019) described three
main results. There were significant differences in wing centroid size and shape between
populations from different geographic areas, and in shape (but not centroid size) between the two
colour forms although the test statistic suggested a smaller difference between colour forms than
between populations. Canonical variate analysis applied to wing shape did not clearly separate
the two colour forms. Using molecular data, specimens of S. pseudospicatum from Iran could
not be distinguished from S. pallipes from the same population or from Belgian S. pallipes.
Finally, they found significant differences between populations in the ratio of the apical ring of
the hind femur (and clearly a test of this ratio between colour forms could not be undertaken as
the ratio for S. pseudospicatum has a mean and variance of zero). In contrast, my results show a
conclusive discontinuity in the variation of leg colour and morphology, different habitat
preferences, and colour variation that may be partly explained by seasonality but not geographic
location. Of these, the pronounced habitat specificity of S. pseudospicatum is presumably under
genetic control expressed through physiology or behaviour, which need not show a morphological
counterpart.
There are three possible reasons for the difference in our results and conclusions. The most
seductive, in that it encompasses both sets of results, is that the two taxa may be rapidly speciating
so that some characters do show genuine differences, notably in leg morphology and colour, but
not in wing or genitalia morphology. If this is the case then S. pseudospicatum has an uncertain
status, and whether it is considered a species or given a lower rank becomes subjective.
Secondly, the two species may represent an example of polyphenism, which is the ability
of animals with the same genotype to develop distinctly different alternative phenotypes without
intermediates, resulting from the environmental conditions encountered during their development
(Nijhout 1999). For instance, colour forms arise under different temperature regimes, as in
76
syrphids (Rotheray and Gilbert 2011) and Lonchoptera (Baud 1973), and in Auchenorrhyncha
feeding on different plant hosts (Claridge and Gilham, 1992). In this scenario, S. pseudospicatum
would be a polyphenotype of S. pallipes induced by saline conditions. One counter to this
suggestion is that both species may be collected together on the same site and day. This suggests
that larvae develop under similar conditions which would be expected to affect both species
equally. I have not examined females in fine detail but other authors concur with my conclusion
that there are no obvious differences in females collected with males of either species, yet if
salinity is operating on one polymorphic species then it affects only male secondary sexual
characters, which makes the suggestion suspect.
The third rather prosaic reason is that one of us is wrong, and that more detailed genetic
analysis using a wider range of genetic loci may be needed to resolve this. If indeed S.
pseudospicatum is shown to be merely a phenotype of S. pallipes, it would represent one of the
most extreme examples within the Palaearctic dolichopodid fauna, having two remarkably
disjunct forms in addition to marked continuous variation within the ringed, hairier form.
I continue the rest of this discussion on the assumption that the two species are distinct.
Clearly, if they are one variable species than much of what is discussed will be inapplicable.
Both S. pallipes and S. pseudospicatum exhibit a wide variation in the colour of the second
and third tergites, although in both species the tergites tend to be either completely dark green or
largely yellow, with little of the gradation that is found in the leg colour of S. pallipes. It is of no
taxonomic value despite Parent (1938) describing the form with dark tergites as S. pallipes and
those with yellow patches as var. pseudospicatum. In my sample, yellow patches were found in
roughly two thirds (69%) of S. pseudospicatum and one third (32%) of S. pallipes. Through the
season, individuals of both species became ‘paler’ on average (that is, more specimens had large
yellow tergite patches) and in S. pallipes the hind femur became paler on average (that is, the
black apical rings became narrower). Early-flying individuals therefore tend to be darker than
those found later in the year. If S. pseudospicatum was a pale form of S. pallipes, it would be
expected to be more frequent later in the season, but this is clearly not the case; their seasonal
distributions are similar (Figs 3, 4).
Several other species have been synonymised with S. pallipes or described as varieties:
Rhaphium hamatum Zetterstedt, 1843, S. uncitarsis Becker, 1902, variety inmaculatus Santos
Abreu, 1929, and subspecies S. pallipes longistylus Grichanov, 2001. Syntormon uncitarsis was
synonymised with S. pallipes by Becker himself, perhaps with some resignation as he says (my
translation) “At last, I too was able to convince myself of these great variations [described by
Loew], and must therefore designate my species uncitarsis from Egypt as only a paler variant”
(Becker 1918). His comment at the end of his 1902 description strongly suggests that it is indeed
the same species as S. pseudospicatum as Becker says (my translation) “This species had so much
in common with the description of S. pseudospicatum that I would not have dared to re-describe
it had Prof. Strobl not established the difference by comparing my types with his own; he
remarked ... that the touching of the eyes of his males in a point under the antennae was not, as I
suspected, caused by shrinkage of the face, but represented the natural condition.” I too have
examined one of Strobl’s males (the holotype, but Becker’s text implies that Strobl had more
males) and I agree with Becker that the eyes touch because the face has shrunk, and it is hardly
in its natural condition. I compared Becker’s description of S. uncitarsis against Strobl’s male,
with which it agrees well apart from the face shape, minor differences in colour pattern that are
within the wide variability of dolichopodids, and the hairs on the hind tibia which Becker
described as absent (Die Hinterschienen haben durchaus keine borstliche Bewimperung).
However, the description of S. uncitarsis does not fit the concept of S. pallipes that I have
established in this paper, that is, with ringed femora and tibia and with moderately long stout hairs
on the hind tibia. It may be relevant that the possible habitat of S. uncitarsis was brackish, in
77
common with that of S. pseudospicatum. In his introduction, Becker gives the localities he visited
in Egypt, and the locality of his S. uncitarsis at “Fayum” was the Fayum Oasis. Although this is
a considerable way from the sea, about 200km, it is probable that Becker visited the saline Lake
Qarun in this oasis area; this lake is now a Ramsar site and probably an attractive place for a
dipterist to have visited on an extended expedition lasting, as Becker’s did, from November to
May. If S. uncitarsis was collected from a brackish site, then its habitat also fits that of S.
pseudospicatum. I have not seen Becker’s specimens, so hesitate to confirm a synonomy of S.
uncitarsis with pseudospicatum, although it seems far more logical than placing S. uncitarsis as
a synonym of S. pallipes.
Zetterstedt (1843) described Rhaphium hamatum which Loew (1850) synonymised with
S. pallipes, but his description of the legs as yellow and the hind basitarsus as often pale at the
base fits S. pseudospicatum, compared to variety ‘a’ of his new species whose hind femora have
black apices, which fits S. pallipes. He goes on to briefly describe two male varieties of S. pallipes
(and a third being represented by females only), based on the colour of the tergites and hind
femora: ‘b’ is apparently a mixture of both S. pallipes and S. pseudospicatum, and ‘c’ is most
likely to be S. pseudospicatum. Zetterstedt also gave a short description of S. pallipes but,
comparing this with his new R. hamatum, I cannot understand why he thought his species was
distinct, although he did seem unsure about the exact identity of Fabricius’s pallipes. I have not
seen his specimens but I guess that they include both S. pallipes and S. pseudospicatum, and
therefore S. hamatum cannot be treated as a synonym of either species until a lectotype is
designated. If it transpires that the most appropriate lectotype fits S. pseudospicatum then
hamatum would become the senior synonym.
Grichanov (2001) described S. pallipes longistylus from Madagascar and stated that it was
closely related to the ‘subspecies’ pseudospicatum, but did not enumerate the differences from
this phenotype but only those from S. pallipes pallipes (the nominotypical subspecies having to
be erected once subspecies are described). The considerably longer arista relative to the
postpedicel of ssp longistylus puts it well outside the range of European S. pseudospicatum, with
a ratio quoted as 41:25, that is, arista 1.64 times the length of postpedicel, compared to the
maximum of 0.86 times in my pseudospicatum sample. Grichanov (2018) retained its status as a
subspecies of S. pallipes (his earlier synonym with the nominotypical pallipes (Grichanov 2013)
was apparently an error, Igor Grichanov pers. comm.), but there are conspicuous differences from
both S. pseudospicatum and S. pallipes that suggest that it is a distinct species. As well as its
Madagascan provenance and the long arista, other conspicuous differences are possessing only 5
strong dc setae (6 in European Syntormon (Parent 1938)), the fore coxae with black apical setae
(not yellow), and yellow hind coxae (not grey with yellow tip).
Santos Abreu (1929) described var. inmaculatus from the Canary Isles. In his very detailed
re-description of the nominal pallipes, the hind femora and tibia have dark apical rings and the
basitarsus is blackish brown or almost completely black, so this must indeed be S. pallipes.
However, his very brief description of his variant distinguishes inmaculatus from pallipes on only
small differences in the colour of the face, frons and sternites and absence of the yellow patches
on the second and third tergites. He did not mention the colour of the hind leg, which he surely
would have done given his very detailed description of the nominal type. His females of var.
inmaculatus differ from the nominal type in lacking yellow tergite patches. I have not seen his
specimens but guess that they are the colour form of S. pallipes without yellow patches on the
tergites. In both S. pallipes and S. pseudospicatum, the occurrence of yellow patches might be
merely polymorphism (although I have not proven this), so var. inmaculatus probably has no
taxonomic status. Santos Abreu himself used the term ‘variety’ for his new taxon, which under
ICZN (1999) rules is infrasubspecific (ICZN Article 45.6.4), but the taxon given in the Palaearctic
catalogue is a trinomial subspecies (Negrobov 1991). This is probably incorrect but is irrelevant
78
if inmaculatus is only a colour variety of two other species. Incidentally, S. inmaculatum has
been cited in Pollet (2011) and repeated in the PESI (2020) portal as immaculatum (with two
‘mm’); this appears to be an unjustified emendation as inmaculatum (with an ‘n’) is acceptable
Latin.
From a conservation perspective, S. pseudospicatum is far too widespread in Britain to
deserve a conservation status but it is part of the assemblage strongly associated with saltmarshes
and brackish sites. Such sites are well represented in Britain compared to some other European
countries but they are not free of pressures from port development, truncation by sea defences,
erosion and rising sea levels (Covey and Laffoley 2002) so identifying suites of specialists of this
habitat is a valuable exercise. Even if S. pseudospicatum is eventually synonymised with S.
pallipes, it remains a considerably more interesting form than many taxa that suffer synonymy,
and should be recorded separately from S. pallipes.
Identification
Negrobov’s key, quoted in the introduction, used a hook character that is difficult to interpret
since the two hooks in specimens that I have examined are mounted on the top of the column.
Their separation from each other varies only slightly but inconsistently in S. pallipes and S.
pseudospicatum; they never arise near the base of the column, but perhaps this is not what
Negrobov meant and maybe details have been lost in translation. Strobl’s type specimen of S.
pseudospicatum differs from Negrobov’s (1971) figure in the hind basitarsus being black in the
apical half, and not entirely yellow as he probably mistakenly illustrated.
Discriminant analysis showed that three characters separate the species with no errors:
ratio of the black ring to total length of the femur, the same ratio for the black ring on the basitarsus
and the average length of the hairs on the tibial fringe. Although the ring on the tibia was not
included in the analysis because it was so closely cross-correlated with the femur ring, it would
also be another reliable character for separating the species. An additional useful character was
the relative thickness of the fringe hairs to the adjacent antero-dorsal seta at the distal quarter of
the tibia, although assessing this requires more care. The ratio of the lengths of the first two tarsal
segments of the hind leg had a strong influence on the separation of the species in the discriminant
analysis but the difference in the means, although highly significant, was trivial and certainly of
no practical use in separating the species. The number of hairs in the tibial fringe was the same
for both species, contrary to the impression given by Loew (1850) and Becker (1918) who
described the fringe of S. pseudospicatum as sparser, or more scantily haired, than that of S.
pallipes. It is not the number but stoutness and length of the hairs that give rise to the differing
impressions of the density of hairing. In fact, the short subsidiary row has more hairs in S.
pseudospicatum than in S. pallipes, although they are finer.
The following rather detailed couplet should separate nearly all specimens, although
usually there will be no need to check more than the first three characters (separated by
semicolons in the couplet). Despite this high level of detail, some outliers will almost certainly
be found. Typical hind tibia, showing the fringes, and hind basitarsi showing the range of
variation in the uprightness of the column with hook are shown in Fig. 8.
_____________________________________________________________________________
Fig. 8. Hind tibia, dorsal face, and two examples of hind basitarsus, anterior face, of
Syntormon pallipes (a, c) and S. pseudospicatum (b, d). Both basitarsi on left-hand side are
from Brittany, France, those on the right-hand side are from Devon, England; tibiae are of
English specimens. The dark ring on the tibia of S. pallipes has been omitted for clarity; see
Fig. 1.
79
80
1 Hind femora and tibia each with a dark apical ring that may extend to their bases (Fig. 1a);
hind basitarsus entirely black (Fig. 8c); anterior fringe of hind tibia composed of longer,
thicker hairs (average length 1.8 x shaft diameter at penultimate antero-dorsal seta, rarely as
short as 1.4 times, hairs nearly as stout as antero-dorsal setae, Fig. 8a); subsidiary apical hair
row dorsal to the main anterior row usually with at least one apical hair as stout as those of
the ad row, more usually 2-3 such hairs (Fig. 1c characters 12 &13); basitarsal column with
hooks usually more upright (proximal edge making an angle of 55-85° with tarsus axis, Fig.
8c) ............................................................................................................................... pallipes
- Hind femora and tibia entirely pale; hind basitarsus pale in about the basal third (Fig. 8d);
anterior fringe of hind tibia composed of shorter, thinner hairs (average length 1.5 x shaft
diameter at penultimate antero-dorsal seta, rarely as long as 1.9 times, hairs only 2/3 as thick
as antero-dorsal setae, obviously thinner, Fig. 8b); subsidiary apical hair row dorsal to the
main anterior row usually with no or only one apical hair as stout as those of the anterior row;
basitarsal column with hooks usually more slanting and curved (proximal edge making an
angle of 45-70° with tarsus axis, Fig. 8d) ………………………………….. pseudospicatum
Acknowledgements
I thank Roy Crossley for fruitful discussion about the reality of S. pseudospicatum and for the
loan of specimens, Richard Lane for learned discussion about morphometric analysis, the
Naturhistorisches Museum, Vienna, Austria, for the loan of the type specimen of S.
pseudospicatum from the Gabriel Strobl collection, Duncan Sivell (Natural History Museum,
London) for arranging this loan and providing access to the NHM Diptera collection and Val
McAtear of the Royal Entomological Society’s library for providing obscure literature. Marc
Pollet made many helpful comments on the first draft, and Igor Grichanov clarified the status of
his Madagascan S. pallipes longistylus. Distribution maps were made using DMAP.
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Changes to the Irish Diptera List (30) – Editor
This section appears as necessary to keep up to date the initial update of the Irish list in Vol. 10,
135-146 and the latest checklist of Irish Diptera (Chandler et al. 2008). Species are listed under
families. The gain of 9 species cited here brings the total Irish list to 3458.
Mycetophilidae
Boletina bidenticulata Sasakawa & Kimura, 1974 (added by Chandler 2020b)
Leia longiseta Barendrecht, 1938 (added by Chandler 2020b)
Manota unifurcata Lundström, 1913 (added by Chandler 2020b)
Mycetophila gibbula Edwards, 1925 (added by Chandler 2020b)
Rymosia connexa Winnertz, 1864 (added by Chandler 2020b)
Platypezidae
Agathomyia lundbecki Chandler in Shatalkin, 1985 (added by R. Mitchell in Chandler 2020a)
Phoridae
Phalacrotophora fasciata (Fallén, 1823) (added by Nelson in the present issue)
Agromyzidae
Phytomyza brunnipes Brischke, 1881 (added by Warrington in the present issue)
Phytomyza stolonigena Hering, 1949 (added by Warrington in the present issue)
References
Chandler, P.J. 2020a. Flat-footed Fly Recording Scheme Newsletter 3 Spring 2020. 4 pp.
Bulletin of the Dipterists Forum No. 89.
Chandler, P.J. 2020b. Fungus Gnats Recording Scheme Newsletter 11 Spring 2020. 8 pp.
Bulletin of the Dipterists Forum No. 89.
