Bul. ent. Res. 78, 317-328
317
Published 1988
The parthenogenetic midge of water supply systems, Paratanytarsus grimmii
(Schneider) (Diptera: Chironomidae)
P. H.
LANGTON
3, St Felix Road, Ramsey Forty Foot, Huntingdon, Cambs., PE17 1YH, UK
P. S.
CRANSTON
ANIC, Division of Entomology, CSIRO, GPO Box 1700, Canberra, ACT 2601, Australia and
formerly Entomology Department, British Museum (Natural History), Cromwell Road, Lon don,
SW75BD, UK
P.
ARMITAGE
Freshwater Biological Association River Laboratory, East Stoke, nr Wareham, Dorset, UK
Abstract
Chironomid midges have been known to include parthenogenetic species
for over a century. One of these species, Paratanytarsus grimmii (Schneider),
cited under several different names here shown to be junior synonyms, has
attained some notoriety as a pest. Its occurrence as a supposedly paedogenetic (actually pharate adult parthenogenetic) inhabitant of water distribution
systems is discussed and related to its more usual occurrence in a variety of
small water bodies including aquaria. New synonymy is proposed and a
lectotype designated.
Introduction
For over a century it has been known that some Chironomidae (non-biting midges) are
able to reproduce parthenogenetically (Grimm, 1870, 1871; Zavfel, 1907; Johannsen,
1910). The phenomenon remained a scientific curiosity, albeit well studied, until the late
1930s, when a chironomid midge, widely distributed through the drinking water supply
system of an unnamed German city, was found to be parthenogenetic. The pharate adult
was able to lay fertile eggs within the pupa, a phenomenon sometimes erroneously referred
to as paedogenesis. As a sanitary problem, this provoked intensive study, detailed by
Kruger (1941), but the infestation disappeared only when the water froze within the mains
pipes. Larvae and pupae of parthenogenetic midges within the water supply recurred in
eastern England in the 1970s (Williams, 1974) and was recognized as widespread in
southern England within the decade. In 1986, an infestation occurred in Cyprus and there
is accumulating evidence that the problem is widespread in other countries.
Taxonomic background
Identification of the species involved has proved troublesome, partially because there
are no males, the stage upon which traditional taxonomic judgements have been made.
Additionally, it has proved difficult to trace specimens examined by previous workers.
Furthermore, too great an emphasis was given previously to the failure of the nuisance
318
p, H, LANGTON, p, S, CRANSTON and p, ARMITAGE
species to eclose, despite evidence of morphologically inseparable parthenogenetic populations with demonstrated facultative eclosure and variable proportions of eclosed and
uneclosed egg-laying females,
In the years since the first British reports of this nuisance, we have attempted to
resolve the confused nomenclature of the chironomid species involved. This has entailed
maintaining cultures derived from nuisance and natural populations, observing the behaviour over many generations and analysing the morphology of the species in relation to
previously published and historic materiaL It is our conclusion that there is a single species
involved, Paratanytarsus grimmii (Schneider), with relatively homogeneous morphology in
all stages and with only minor variations throughout its almost worldwide geographic range
and habitats, We therefore concur with Lindeberg's (1971) implicit view that "all these
forms are perhaps strains of one species"; however, Lindeberg refrained from pursuing the
nomenclatural conclusions, Despite the problems inherent in recognition of parthenogenetic species, we feel justified in viewing P. grimmii as one virtually world-wide 'weed'
species,
Abbreviations
Repositories are abbreviated in the text as follows:
ANIC Australian National Insect Collection, Canberra, Australia;
BMNH Entomology Department, British Museum (Natural History), London, UK;
CUIC Cornell University Insect Collections, Ithaca, New York State, USA (Dr J.
Leibherr);
DHDE Private collection of D. H. D. Edward, University of Western Australia, Nedlands, W. Australia;
FBA Freshwater Biological Association River Laboratory, East Stoke, nr Wareham,
Dorset, UK;
PHL Private collection of P. H. Langton;
ZSM Zoologische Staatssammlung, Munich, German Federal Republic (Dr F. Reiss).
Paratanytarsus Thienemann & Bause
Paratanytarsus Thienemann & Bause in Bause, 1913; 120. [For discussion of authorship see
Reiss & Siiwedal, 1971: 73-74.] Type-species: Tanytarsus lauterborni Kieffer. 1909, des.
Reiss & Siiwedal, 1981: 74.
Stylotanytarsus Kieffer, 1921a: 276. Type-species: Tanytarsus bau.~els
Bause, 1913: 97
[Kieffer, 1922: 96], here designated.
The genus-group name Stylotanytarsus has a confused history arising from non-sequential
publications. The first reference to Stylotanytarsus was in a key (Kieffer, 1921a) with no
indication of included species, but later in the same year in another key (Kieffer, 1921b)
two species were included in Stylotanytarsus, bauseellus "Kieffer" and boiemicus "Kieffer".
These two names were not accompanied by descriptions, and it was not until the following
year (Kieffer, 1922) that they were described from reared females as be\cnging to the genus
Paratanytarsus "Bause", It is evident that the three publications (Kieffer, 1921a, 1921b,
1922) appeared in the reverse order to their production: Kieffer intended the genus
Stylotanytarsus for bauseellus and boiemicus described in Paratanytarsus in an intended
earlier publication. However, it is evident that Kieffer had earlier provided the names
bauseellus and boiemicus to Bause who unintentionally made the names available by
publishing them, accompanied by illustrations of the pupae. Thus the authorship and date
of bauseellus and boiemicus must be Bause, 1913. We select Tanytarsus bauseellus Bause,
1913: 97 (with pupal illustration on fig. 73) as the type of Stylotanytarsus Kieffer. 1921a.
Thus, although the immature stages were known, Kieffer based Stylotanytarsus on female
adults. Further references to Stylotanytarsus after Kieffer (1922) relate to many of the
species names listed under Paratanytarsus grimmii (Schneider) below and, almost exclusively,
refer to parthenogenetic species of Paralanytarsus that lack a pupal thoracic horn, However,
CHIRONOMID OF WATER SUPPLY SYSTEMS
319
the confusion over dissimilis originating from Johannsen (1905, 1937) (additionally detailed
below) also impinges on Stylotanytarsus. Thus, when Kruger (1941) discussed Stylotanytarsus,
his generic definition was based upon the pupal abdominal spine pattern, and in addition to
the parthenogenetic 'boiemicus' group, he erected a second, 'securifer', species-group based
upon Tanytarsus dissimilis Johannsen. In addition to dissimilis, Kruger included Tanytarsus
securifer Goetghebuer, 1934, based upon pupae and adults named as this species, reared by
Nietzke (1938). Examination of examples of this species in ZSM (but not Goetghebuer's
type) shows this to be identical with dissimilis Johannsen.
The larva and adult female of Stylotanytarsus cannot be differentiated from those of
Paratanytarsus, and the pupa clearly belongs to the Paratanytarsus inopertus group of Pinder
& Reiss (1986), differing only in lacking a thoracic horn. We do not believe that this loss of
a thoracic horn warrants generic status and therefore treat Stylotanytarsus as a junior
synonym of Paratanytarsus. This treatment is not new, but conflicts with the opinion
expressed by Reiss & Sawedal (1981).
Paratanytarsus grimmii (Schneider)
(Chironomus-Art Grimm, 1870: 1)
Chironomus grimmii Schneider, 1885: 301. Type(s): Not stated [? USSR] [believed lost].
Tanytarsus dissimilis Var. a Johannsen, 1905: 293. Syn. n.
Tanytarsus boiemicus Bause, 1913: 97, fig. 74; Johannsen, 1937 (for T. dissimilis VaL a.
Johannsen, 1905). Type(s): CZECHOSLOVAKIA: Hradec Kralove [believed lost]. Syn. n.
Tanytarsus bauseellus Bause, 1913: 97, fig. 73. Type(s): GERMAN FEDERAL REPUBLIC:
Westphalia, nr Munster [believed lost]. Syn. n.
Paratanytarsus boiemicus Kieffer, 1922: 96 (as sp. n.).
Paratanytarsus bauseellus Kieffer, 1922: 96 (as sp. n.).
Paratanytarsus grimmii Schneider; Thienemann, 1929: 115.
Tanytarsus virgo Goetghebuer, 1934: 291. Type(s): GERMAN FEDERAL REPUBLIC: Bremen
[not examined]. Syn. n.
Tanytarsus chlorogyne Goetghebuer in Goetghebuer, 1938: 113 (nom. nov. for virgo
Goetghebuer, 1934 not Kieffer, 1917 [jun. homonym]).
Stylotanytarsus inquilinus Kruger, 1941: 248. Lectotype (here designated): GERMANY:
unnamed "mitteldeutschen Industrienstadt" [examined]. Syn. n.
Stylotanytarsus luteola Goetghebuer in Thienemann, 1950: 162. Type(s): AUSTRIA: Lunz
[not examined]. Syn. n.
Lundstroemia parthenogenetica Freeman, 1961: 721; Edward, 1963. Holotype: AUSTRALIA:
Western Australia, Lake Gwellup [Paratypes, examined, same locality]. Syn. n.
Paratanytarsus parthenogeneticus (Freeman); Glover, 1973; Sasa, 1979.
Lundstroemia agameta Forsyth, 1971: 137. Holotype: NEW ZEALAND [not examined]. Syn.
n.
Paratanytarsus sp. Anden Reiss, 1972: 60.
The specific synonymy within this taxon is as complex as any in the notoriously confused
nomenclature of the Chironomidae. As is often the case, types have not been retained or
have been destroyed. However, excellent descriptions and figures of the pupae often
facilitate recognition. The summary of our nomenclatural decisions below is followed by a
discussion of the history and justification of the nomenclatural conclusions made.
The taxon was first recognized by Grimm who described its morphology and biology as
Chironomus-Art, first in German (Grimm, 1870) then later in English (Grimm, 1871). The
species was named subsequently as Chironomus grimmii by Schneider, who added little
further details, and no type has been found.
Zavrel, who reared the parthenogenetic species whose pupae were subsequently described
by Bause (1913) and adults by Kieffer (1922) as boiemicus, discussed partheno- and
paedogenetic chironomids (Zavfel, 1907). Both he, Johannsen (1910) and Bause (1913: 17,
in an extensive footnote) recognized the parthenogenetic chironomid described by Grimm
(1870) as belonging to the Tanytarsini. However, Bause (1913), who used the immature
320
P. H. LANGTON. P. S. CRANSTON and P. ARMITAGE
stages to describe boiemicus and bauseellus and to include them in his Tanytarsus lauterborni
group (=Paratanytarsus), did not pursue the similarity to Grimm's parthenogenetic midge.
Munsterhjelm (1920) and Thienemann (1929) did recognize the close relationship and
Thienemann placed grimmii in the 'Paratanytarsus' group of genera.
Despite Thienemann's virtual resolution of the problems in this 1929 paper, on many
subsequent occasions when parthenogenetic Tanytarsini were encountered, further new
names were proposed. For example, Goetghebuer (1934) described Tanytarsus virgo for a
parthenogenetic midge from an aquarium in Germany without comparison with any
other species. The immature stages were indistinguishable from bauseellus and boiemicus
(Thienemann, 1935), as were those of Stylotanytarsus luteola described by Goetghebuer in
Thienemann (1950). No types of these species have been examined, but the immature stages
preserved in the ZSM confirm the identity.
The most thorough attempt to understand the taxonomy (and some nomenclature) was
that of Kruger (1941), who investigated the species causing nuisance in German water
distribution pipes. Kruger believed that he could recognize several parthenogenetic taxa,
including inquilinus that he described as new, based upon subtle differences in the pupa,
particularly the numbers of filamentous setae (30--40) on the anal lobe. Syntypic slidemounted material of inquilinus exists in ZSM, and lecto- and paralectotypes are recognized
here (see below). Re-examination of this material shows greater variability in setal counts
and size than Kruger had published, and we are unable to confirm either the pupal separation
of inquilinus or the existence of further species suggested by Kruger. The material falls
within the range of morphological variation and biology that we recognize for grimmii.
A great deal of subsequent confusion over this taxon, and the genus Stylotanytarsus
erected for the parthenogenetic taxa related to Paratanytarsus, is due to Johannsen. He
described Tanytarsus dissimilis with a variety a (Johannsen, 1905), subsequently recognizing
this variety to be parthenogenetic and identical with T. boiemicus (Johannsen, 1937). In
the latter paper, Johannsen (1937) redescribed the immature stages of dissimilis, recognized
the species as being both parthenogenetic and paedogenetic, and placed it in the Paratanytarsus group. Unlike the European parthenogenetic taxa we now recognize as all belonging to
grimmii, Johannsen's dissimilis was described as able to produce males and possessing a
distinct pupal thoracic horn. Examination of Johannsen's material in curc shows that his
rearing culture(s) contained two species: the holotype male of dissimilis belongs to
Paratanytarsus and is identical to P. con/usus Palmen, 1960 (and therefore a senior synonym
thereof) while dissimilis var. a (that he later recognized as boiemicus) is identical with P.
grimmii. Johannsen's (1937) concept of dissimilis included both species; only the true
dissimilis possesses a pupal thoracic horn. The confusion, further detailed under Stylotanytarsus above, probably arose through the abdominal spine patterns on the two species being
extremely similar.
More recently described species, P. parthenogeneticus (Freeman, 1961) from Australia
and P. agametus (Forsyth, 1971) from New Zealand, were described without reference to
earlier names. We concur with Sasa's (1979) recognition that the Japanese population he
studied demonstrated the identity of Freeman's parthenogenetica and Forsyth's agameta.
Type material of adults and examination and reference to descriptions of the immature
stages by Edward (1963), Forsyth (1971) and Sasa (1979) convince us that, in turn. these
are junior synonyms of grimmii.
Description
Female (n = 50+). The female conforms to the generic diagnosis of Saether (1977)
and may be identical to Saether's Paratanytarsus sp. B (Saether, 1977: 145, fig. 68C, D).
Body length 1·1-2·6 mm, wing length 1·3-2·1 mm, light green with pale brown thorax
and legs, darker brown antenna and postnotum.
Antenna with five fiagellomeres, lengths 92-112,56-63,59-72,53-69,59-89 ,um, exceptionally ftagellomeres 4 and 5 partially fused, fiagellomeres 2-4 spindle-shaped. Antennal
ratio 0·22-0·29. Flagel\omeres 1-4 each bearing apically a pair of simple, narrow, sensilla
trichodea of length 33-38 "m.
321
CHIRONOMlD OF WATER SUPPLY SYSTEMS
Palp with segments 3 and 4 subequal, shorter than segment 5.
Wing membrane with slight brown pigment, rather densely covered with macrotrichia.
R2 + 3 absent. Vena rum ratio 1·2:1·3.
Foreleg ratio 1·23: 1·50, Anterior tibial scale absent. Each mid- and hind-leg tibial comb
usually bearing a strong spur, rarely one is missing, Combs nearly contiguous, occupying in
total slightly more than half the circumference of the tibial apex,
Genitalia as in Fig. 1.
Fig, L-Paratanytarsus grimmii, <jl genitalia, ventral view, (Scale bar
100,urn.)
50+) (Fig. 2). The pupa of P. grimmii conforms to the generic diagnosis
Pupa (n
for Paratanytarsus given by Reiss & Sawedal (1981) and Pinder & Reiss (1986).
Body length 2·8-4·0 mOl, yellow-green.
Frontal seta weakly filamentous, 90-165 ,urn long, arising from slight tubercle. Thoracic
horn absent. All dorsocentral (dc) setae ca 100,um long, dcl fine, arising very close to dc2,
these widely separated from proximate dc3 and 4; dc2-4 about 4,um wide, stout and apically
frayed.
Abdominal setal pattern as in Fig. 2. Tergite I without shagreen. Tergite II with
widespread shagreen and posterior hookrow of 60-110 hooklets. Tergite III with paired
medio/postero-lateral groups of ca 40-50-,um-long translucent spines. Tergite IV with anteriomedian dark pigmented group of 25-35 spinules and two groups of longitudinal mediolateral rows of 25-35 ca 50-,um-Iong translucent spines. Tergite V with anterior paired dark
pigmented groups of 18-26 spinules. Tergites VI-VII with median shagreen, tergite VIII
with only antero-Iateral patches, tergite IX with weak anterior field of shagreen.
C..omb on postero-Iateral margin of tergite VIII brown, 25-45,um wide, bearing 4--10
marginal teeth. Filamentous lateral setae on segments IV-VIII 2-3, 4 (3), 4, 4 and 5,
respectively.
322
p, H. LANGTON, P. S. CRANSTON and p, ARMITAGE
Fig. 2,-Paratanytarsus grimmii, pupal abdomen, dorsal view. (Scale
bar 200 ,um, )
Anal lobe with 28-47 marginal filamentous setae (median of 41 in 33 British examples,
probably a little lower in German examples).
Fourth-(jinal)-instar larva (n = 50+) (Figs. 3-12). The larva of P. grimmii conforms
to the generic diagnosis for Pararanytarsus given by Pinder & Reiss (1983).
Body length 2·8-3· 7 mm, tinged with pink, with yellow head capsule 270--380 pm long;
mentum, mandibular teeth and apical half of mola mid-brown.
Antenna (fourth instar: Fig. 6; first-third instars: Figs 3-5) is five-segmented, segment
lengths: 96--106,21-26, l(}-B, 3-7,3-6 pm. Antennal ratio 1·93-2·2. Antennal blade 3540 pm. Lauterborn organs small, 4-5 pm long, on short petiole of 2-3 pm.
Premandible 66--82 pm long, with sharp apical tooth, broader subapical tooth and slight
inner tooth.
Mandible (fourth instar: Fig. 8; first instar: Fig. 7) 125-148 pm long; outer tooth much
shorter than apical tooth; mola angled.
Mentum (fourth instar: Fig. 12; first-third instars: Figs. 9-11) 81-89 pm wide, with slightly
trifid median tooth 13-15 pm wide. Ventromental plate elongate, 105-112 pm long, maximally
20--23 pm wide; plates almost in contact medially.
Abdomen: all claws on anterior and posterior parapods simple, approximately 15 claws
on posterior parapod. Procerci about 45 pm high and20pm wide, subapically darkly pigmented,
bearing apically eight setae of maximum length 450--500 pm. Anal tubules subovate. 80-100 pm long, much shorter than posterior parapods.
CBlRONOMID OF WATER SUPPLY SYSTEMS
323
Figs 3-6.-Paratanytarsus grimmii, larval antennae; 3, first instar; 4, second instar; 5, third
instar; 6, fourth instaL (Scale bars = 25 ,urn.)
Diagnosis
The genus ['aratanytarsus is known well only in the adult male and pupal stages; the
larvae and adult females are rarely described, never adequately for discrimination from
related species. For this reason, the descriptions given above contain some details that are
of unknown diagnostic relevance. In this parthenogenetic species, only the pupa can be
recognized with certainty; in Pinder & Reiss (1986), this stage keys to the inopertus speciesgroup, differing principally in lacking a thoracic horn and less distinctly in the tergal spine
pattern.
Our inability to discriminate females of P. grimmii from those of congeneric species
means that we are unable to recognize un associated females with certainty. Glover's (1973)
observation that P. grimmii (cited as P. parthenogeneticus) differs from Australian congeners
in the reduction in macrotrichia at the base of wing cell ml + 2 cannot be substantiated even
within the Australian fauna and the character cannot be used to discriminate elsewhere.
Thus, we list unassociated females along with unassociated larvae after the next section.
Type-material examined
In the Zoologische Staatssammlung, Munich, there are many slides of P. grimmii bearing
inadequate data labels that may relate to type material of some nominal taxa. Amongst
these are two slide preparations labelled "Stylotanytarsus 10.6. (II)" and another "Stylotanytarsus 11.7. (III)" in one hand, with "inquilinus Kg" in different ink. Comparison with
known examples of handwriting indicate that the original label was written by Kruger, the
species name by Thienemann. Despite the lack of further data, these slides appear to be
syntypes of inquilinus Kruger, and a lectotype is here designated and the slide so labelled
on a red Zoologische Staatssammlung, Munchen, label. The slide comprises a female
indicated under a coverslip containing two other females on the slide marked "11.7. (III)".
Two further slides contain three females under one coverslip and two under an adjacent
coverslip, and three pupal exuviae, respectively; these (and the remaining two on the
slide containing the lectotype) have been labelled appropriately as paralectotypes of
Stylotanytarsus inquilinus. All material has been returned to ZSM.
Holotype male, a slide labelled "OAJ Lot 1519, Tanytarsus d dissimilis Johannsen,
Elston Ice Pond, Ithaca, N.Y. Oct. Holotype No. 2363 Cornell University Dept. of
Entomology". Returned to CUIC.
324
p, H. LANGTON, p, S, CRANSTON and p, ARMITAGE
~9'
Il"
~
I
I
12
'
I----i
Figs 7 & 8.-Paratanytarsus grimmii, larval mandible; 7, first instar; 8, fourth ins tar. Figs 912,-Paratanytarsus grimmii, larval menta; 9, first instar; 10, second instar; 11, third instar;
12, fourth instar. (Scale bars 25 11m.)
The only other nominal taxon discussed in which type material exists and has been
examined is that of Lundstroemia parthenogenetica Freeman. The following have been
studied: 10 female paratypes, pinned, Australia, Western Australia, Lake Gwellup, viii &
ix.1958 (D. H. D. Edward) (BMNH). Associated pupae confirm the synonomy to grimmii.
Other material examined (all slide-mounted in Euparal or Canada Balsam unless stated
otherwise)
AUSTRALIA: 1 ,?, 4 pupae, University of Sydney, McMaster Lab. "Dr J. Boray's
aquarium", 22.ix.1966 (A. L. Dyce) (ANIC); 5 pupae, 2 larvae, 25.x.1961, 'ex-lab. culture'
(D. H. Colless) (BMNH); numerous pupae, Western Australia, Lake Gwellup. viii &
ix.1958 (D. H. D. Edward) (DHDE). CANADA: 1 S?, 2 pupal exuviae, New Brunswick, St
Andrews Biological Station, 29,iii.1977 "in tremendous numbers blocking filters of water
recirculating system for aquaculture" (M. 1. Dodswell) CH 3354 (CNC); 1 S?, 1 pupa, 1
pupal exuviae, 2 larvae, Ontario, University of Windsor, 8.iii.1983, "lab. colony" (P.
Hebert). CHILE: many pupal exuviae and S? ,?, Punta ArenasIMagellanes, Rio Tres Brazos,
22.ii.1954 (L. Brundin); many pupal exuviae and s?,?, Rio Paine/Magelianes 15,ii.1954 (L.
Brundin); many pupal exuviae and,? ,?, N.W. Tierra del Fuego, Rio Fortuna and Rio
Oscar, 6-7.ii.1954 (L. Brundin) (all ZSM). CYPRUS: 1 ,?, 8 pupae, 15 larvae, Xylotimbou
CHIRONOMID OF WATER SUPPLY SYSTEMS
325
Water Supply, "ex-mains" (G. Ophanides); 3 <?, 2 larvae, Satira village "water distribution
system" (G. Ophanides) (BMNH). GERMAN FEDERAL REPUBLIC: numerous larvae and
pupae with inadequate data but including: PIOn, "Thienemann's garden" & "algen kulture
Kemforschungs-aulage lillich, x.83" (ZSM). ITALY: 2 pupae, 13.iv.1981 (B. Rossaro) (ZSM);
PERU: pupal exuviae and <?<?, Puna Bay near Chucuito, 16.iv.1954 (L. Brundin) (ZSM).
TURKEY: 2 pupae, Istanbul, xi.1943 (Bott) (ZSM); UK: 3 <?, Essex Water Co., 26.x.1973
"2nd generation adult" (P. H. Langton) (BMNH); many larvae, pupae, adult <?, same
source, different dates (PHL); 2 larvae, 1 pupa, same source, 25.vii.1973 (P. S. Cranston)
(BMNH); 5 larvae, 1 pupa, West Sussex, West Hoathly, "ex-water mains" (Stallybrass)
(BMNH); 5 larvae, London, BMNH, "ex-water taps" (P. S. Cranston) (BMNH); 4 <?, 8
pupae, 13 larvae, Dorset, FBA "ex-aquarium" (P. Armitage) (BMNH), further material
(FBA). USA: 1 larval & associated pupal exuviae, 15.ix.191O, Maine, Orono, OAJ Lot
1659; 1 <? with associated pupal exuviae, same source, 22.x.191O, OAJ Lot 1648; 1 pupal
exuviae, same source, x.191O, OAl Lot 1646; 4 pinned <?, same source, ix.-x.1910 (All
CUIC).
Material probably P. grimmii but unconfirmed by pupa:
USA: 3 larvae, Washington State, Mt. St. Helens, hot sulphurous pool near shores of
Spirit Lake, 3.vii.l985 (P. S. Cranston) (BMNH). AUSTRALIA: 21 pinned <? <?' NSW, Sydney,
20.x.1966, "ex-culture" (A. L. Dyce); 3 pinned 9<?, ACT, Black Mt., l.ix.1960, "light
trap" (I. F B. Common); Victoria, Ocean Grove, 12.xi.1962 (J. Martin) (ANIC).
Distribution
Australopacific Region: widespread in Australia from Western Australia to Queensland,
sooth to Victoria (Glover, 1973, as P. pathenogeneticus). Neotropical Region: from Lake
Titicaca in the north to north-western Tierra del Fuego in the south (Reiss, 1972, as
Paratanytarsus sp. Anden). Palaearctic Region: widespread from Britain to Turkey; Japan.
Nearctic Region: eastern USA and Canada, with a possible record from western USA (see
above). Unknown from the Afrotropical Region.
to
Biology
Accounts of the biology of P. grimmii have been given by Grimm (1870) and, under a
variety of the names listed in the nomenclature section, by Thienemann (1935), Krilger
(1941), Edward (1963), Forsyth (1971), Langton (1974) andSasa (1979). These accounts
differ only in minor details and are summarized here with additional unpublished information
from the authors.
The eggs are laid as a single row in a gelatinous sheath, the egg-string, and lie at an
angle of 40-45 0 to the longitudinal axis of the sheath. The first egg-string is laid within 2 h
of eolosion (if ecIosion does take place), in some cases within a few minutes. Usually, a '
second string is laid later, within :;.t. h, and even eight strings have been reported from a
single female of one clone ('parthenogeneticus'). The fly lays its eggs while resting on the
water surface, the process taking about 30 s to complete, during which time the abdomen is
angled away from the water surface. The tightly coiled fawn-coloured egg-string is formed
on the end of the abdomen, which is then lowered to the water surface, where the string
may float for a short time before sinking. On oeeasions, the egg string immediately contacts
the water as it forms, as a slight undulate cord, dropping immediately to the bottom upon
completion. Few adults are still alive two days after eclosion.
The number of eggs in each egg-string depends probably as much on larval nutrition as
on the clone. Most of the reported values lie in the range 13-80, with a total number of
eggs laid by a single midge in the range 100-175, but a total of 13 for 'inquilinus' and of 352
for 'parthenogeneticus' are recorded.
On contact with the water, the gelatinous sheath rapldly swells, displaeing the enclosed
eggs from their orderly arrangement, uncoils and becomes transparent, the egg-string
appearing milky or yellowish to the unaided eye due to the enclosed eggs. The initial
326
P. H. LANGTON. P. S. CRANSTON and P. ARMITAGE
diameter of the egg-string is about O· 2 mm, but it may swell to 1 mm when it has absorbed
water.
The newly laid eggs are 0·18-D·35 mm long and 0·06-0·12 mm wide, larger adults laying
larger eggs. Grimm (1870) reports that during embryonic development the eggs stretch to
accommodate the developing larva, an egg of 0·22 mm reaching 0·27 mm before hatching.
The young larvae hatch, tail first, 48-100 h after the eggs were laid. After a short period,
during which they disperse by crawling, these first-instar larvae build silken tubes fastened
to the substrate along their length, except for the mouth opening which may be raised. In
these they live, extending the anterior end of the body from the tube to scavenge on a
variety of organic debris.
There are the usual four instars recognizable by head-capsule lengths of 9G-I05, 12G150, 18G-265 and 27G-380 ,urn. The fully grown larva has a body length of 3-4 mm and width
of 0·5 mm, with pale brown head and greenish body, often with a pink tinge developing in
older larvae.
As the larva increases in size, it extends its tube, giving a final form of the tube as a
long rambling hollow cone, about 0·5 mm in diameter at its origin, increasing gradually to
about 0·75 mm at its termination, and as much as ten times as long as the larval body. The
tube is embellished with small particles of organic or mineral matter, which are actively
stuck to the circumference of the opening as the tube is extended. Often, however, a larva
may leave its tube and start again elsewhere, so that complete tubes are rare even in the
laboratory.
The duration of the larval stage depends upon the temperature of the water and food
availability. The first moult occurs 1-7 days after hatching, the second after 3-10 days and
the third after 14-16 days. The shortest recorded period between hatching and pupation is
17 days.
Prior to pupation, most of the tube is eaten to leave a section long enough to protect
the pupa, about 6 mm long and 0·8 mm broad, the openings of which are narrowed to leave
a small orifice through which a stream of water is maintained by undulations of the pupal
body.
The 'pupal' stage is of short duration; Kruger (1941) recorded 25 min to 4·5 h. How
long the free pupal stage lasts is uncertain, if indeed it exists, for all 'pupae' are in fact
pharate adults enclosed within the pupal exuviae. The pharate adults leave the pupal tubes
and swim vigorously for 30 min to over an hour, after which they hang vertically from the
water surface for about 20 s, when the thoracic region noticeably swells to the unaided eye.
Within a minute from the final cessation of swimming, the eclosed adult is resting on the
water surface or flying to rest nearby.
If the pharate adult fails to eclose, it will lay its eggs while still enclosed within the pupal
exuviae, the process erroneously referred to as paedogenesis by Zavrel (1907) and Johannsen
(1910). The egg-string swells as it absorbs water and ruptures the exuvial abdomen, allowing
the larvae to escape when they hatch.
Generation times vary greatly for the reasons given above. The effect of temperature is
given by Edward (1963): at median temperatures of 12·5, 16 and 25°C, the life cycle is
completed in 32-40, 25-35 and 19-27 days, respectively. Temperatures above 27°C are
progressively more lethal, and the larvae cannot survive freezing. Partly starved populations
may take months to complete development, and then smaller adults are produced.
In nature, the species inhabits shallow standing water; large populations occur frequently
in small artificial garden fishponds, where the larvae are found in mats of filamentous algae
or on the substrate close to the water's edge. They also occur in the shallow margins of
lakes and reservoirs amongst emergent vegetation. Their pupal exuviae are rarely collected
by skimming the water surface or by collecting flotsam, but examination of the filamentous
algae reveals the trapped exuviae. The capacity to lay eggs without eclosion has enabled P.
grimmii to colonize water distribution systems, and its frequent occurrence in aquaria may
be due to its arrival in tap water. It has been observed that P. grimmii outbreaks in water
distribution systems follow the replacement of old filters. This may be due to filter
replacement dislodging immature stages of P. grimmii or to the new filters eXcluding the
CHIROl"OMID OF WATER SUPPLY SYSTEMS
327
continuous supply of predators that cannot maintain populations within the water-filled
pipes.
Discussion
A widely distributed parthenogenetic species which is a weak flier, living only for a short
time in the most probable distribution phase and which has been in existence for a very
great number of generations is likely to have been subject to minor mutations which affect
its biology and morphology. One would therefore expect that P. grimmii occurs in a
multiplicity of clones different to some extent and perhaps even coexisting in the same water
body. Although certain of these clones may be preadapted for unusual habitats such as
water mains, it would be a futile exercise to attempt to isolate and name clones on minute
differences in structure and/or biology. The problems in doing so are compounded by
environmentally induced variation during the life cycle, beginning perhaps even with the
unlaid egg. Populations developing in small ponds, water distribution systems or carefully
tended laboratory populations are more homogeneous in appearance, dimensions and
biology. An example will suffice: 'parthenogeneticus' appears from the Australian material
of Edward (described by Freeman (1961) and Edward (1963)) to be particularly recognizable
in being larger and more fecund than other described 'species', including the New Zealand
P. agametus (Forsyth, 1971). Sasa reported a similar clone to parthenogeneticus from Japan,
which under different conditions produced the complete range of morphological variation
between the two antipodean 'species'.
Acknowledgements
We are grateful to Dr F. Reiss (ZSM) for loan of material and taxonomic discussions
and to Dr J. Leibherr for the loan of Johannsen material from CUIC. We also wish to
thank Angela Matthews for providing the illustrations.
References
BAUSE,
"
E. (1913). Die Metamorphose der Gattung Tanytarsus und elmger verwandter
Tendipedidenarten.-126 pp. lnaug. Diss. Zool. Inst. Westfalische Wilhelms-UniversiUit zu
Munster.
EDWARD, D. H. D. (1963). The biology of a parthenogentic species of Lundstroemia (Diptera:
Chironomidae), with descriptions of the immature stages.-Proc. R. enl. Soc. Land. (A) 38,
165-170.
FORSYTH, D. J. (1971). Some New Zealand Chironomidae (Diptera).-1. R. Soc. N.Z. L 113-144.
FREEMAN, P. (1961). The Chironomidae (Diptera) of Australia.-Aust. 1. Zool. 9,611-737.
GLOVER. B. (1973). The Tanytarsini (Diptera: Chironomidae) of Australia.-Aust. 1. Zoo/., Suppl.
Ser. no. 23, 403-478.
GOInGHEBUER, M. (1934). Ceratopogonidae et Chironomidae nouveaux ou peu connus d'Europc
(cinquieme note).-Bull. Annis Soc. r. ent. Belg. 74,287-294.
GOETGHEBUER, M. (1938). Tendipedidae-Tendipedinae [partj.-Fliegen palaearkt. Reg. Be, 73-128.
GRIMM, O. VON (1870). Die ungeschlechtiche Fortplanzung einer Chirollomus-Art und deren Entwicklung aus dem unbefruchteten Ei.Zap. imp. Akad. Nauk 7 (15),124.
GRIMM, O. VON (1871). On the agamic reproduction of a species of Chironomus. and its development
from the unfecundated egg.-Ann. Mag. nat. Hist. 8,31-45. 106115.
JOHANNSE:I, O. A. (1905). Aquatic nematocerous Diptera. II.pp.76327 in Needham, I. G.,
Morton, K. I. & Johannsen, O. A. (Eds). May flies and midges of New York.-Bull. N. Y.
51. Mus. no. 86, 331 pp.
JOHANNSE:I, O. A. (1910). Paedogenesis in Tanytarsus.-Science, N. Y. (N.S.) 32, 768.
JOHANNSEN, O.A. (1937). Aquatic Diptera. Part III. Chironomidae: subfamilies Tanypodinae,
Diamesinae, and Orthocladiinae.Mem. Cornell Univ. agric. Exp. Stn no. 205, 84 pp.
KIEFFER. J. J. (1909). Diagnoses de nouveaux Chironomides d'AlIemagne.-Bull. Soc. Hist. nat. Metz
26,3756.
KIEFFER, J. 1. (1917). Chironomides d'Amerique conserves au Musee National Hongrois de
Budapest.Annls hist.-na(. Mus. flatn. hung. 15,292-364.
KIEffER, J. J. (1921a). Synopse de la tribu des Chironomariae.-Annis Soc. scient. Brux. 40, 269276.
328
P. H.
LANGTON. P. S. CRANSTON and P. ARMITAGE
KIEFFER, J. J. (1921b). Chironomides de I'Afrique Equatoriale (I" partie).-Annls Soc. em. Fr. 90,
156.
KIEFFER, J. 1. (1922). Chironomides nouveaux ou peu eonnus de la region palearetique.-Annls Soc.
scient. Brux. 42,71128.
KRUGER, F. (1941). Parthenogenetisehe Stylotanytarsus Larven als Bewohner einer Trinkwasserleitung.
(Tanytarsus-Studien III: die Gattung Stylotanytarsus).-Arch. Hydrobiol. 38,214253.
LANGTON, P. H. (1974). On the biology of the parthenogenetic Paratanytarsus breeding in the Essex
Water Company distribution system.-Wat. Treat. & Exam. 23,230231.
LINDEBERG, B. (1971). Parthenogenetic strains and unbalanced sex ratios in Tanytarsini (Diptera,
Chironomidae).Ann. zool. fenn. 8,310317.
MUNSTERHJELM, G. (1920). Om Chironomidernas agglaggning oeh aggrupper.-Acta Soc. Fauna nora
!enn. 47 (2), 1174.
NlETZKE, G. (1938). Die Kossau. Hydrologisehefaunistisehe Untersuchungen an schleswigholsteinischen Fliessgewassern.Arch. Hydrobiol. 32, 174.
PALMEN, E. (1960). Paratanytarsus-Arten (Dipt., Chironomidae) aus dem flmesohalinen und oligohalinen Brackwasser des Finnisehen Meerbusens.Suom. hyont. Aikak. 26,280291.
PINDER, L. C. V. & REISS, F. (1983). The larvae of Chironominae (Diptera: Chironomidae) of the
Holaretie region. Keys and diagnoses.-Entomol. Scand. Supp!. no. 19,293435.
PINDER, L. C. V. & REISS, F. (1986). The pupae of Chironominae (Diptera: Chironomidae) of the
Holarctie region. Keys and diagnoses.-Entomol. Scand. Supp\. no. 28, 299456.
REISS, F. (1972). Die Tanytarsini (Chironomidae, Diptera) Slide hiles und Westpatagoniens. Mit
Hinweisen auf die TanytarsiniFauna der Neotropis.Stud. neotrop. Fauna 7, 4994.
REISS, F. & Si\WEDAL, L. (1981). Keys to males and pupae of the Palaearctic (excl. Japan)
Paratanytarsus Thienemann & Bause, 1913, n. comb., with descriptions of three new species
(Diptera, Chironomidae).-Entomol. Scand. Supp\. no. 15,73104.
SAETHER, O. A. (1977). Female genitalia in Chironomidae and other Nematocera: morphology,
phylogenies, keys.Bull. Fi~h.
Res. Bd Can. 197, 209 pp.
SASA, M. (1979). A morphological study of adults and immature stages of 20 Japanese species of the
family Chironomidae (Diptera).-Res. Rep. Natn. Inst. Env. Stud. no. 7, 1149.
SCHNEIDER, A. (1885). Chironomus Grimmii und seine Parthenogenesis.Zool. Beitr. I, 301302.
THiENEMANN, A. (1929). ChironomidenMetamorphosen. II. Die Sectio Tanytarsus genuinus.-Arch.
Hydrobiol. Planktonk. 20,93123.
THIENEMANN, A. (1935). ChironomidenMetamorphosen. XII.-Dt. ent. Z. 2,8696.
THlENEMANN, A. (1950). Lunzer Chironomiden. Ergebnisse von Untersuchungen der stehenden
Gewasser des Lunzer Seengebietes (Niederosterreich).Arch. Hydrobiot. Suppl. no. 18, 1202.
THIENEMANN, A. (1951). Tanytarsus-Studien II. Die Subsectio Paratanytarsus. Auf Grund der
nachgelassenen Papiere Friedreich Wilh. Carl Krligcr's.Arch. Hydrobiol. Supp\. no. 18,
595632.
WILLIAMS, D. N. (1974). An infestation by a parthenogenetic ehironomid.Wat. Treat. & Exam. 23,
215229.
ZAvI\EL, J. (1907). Paedogenese a parthcnogenesc u Tanytarsa.Cas. ceske Spot. em. 4, 6465.
(Received 12 October 1987)
© C·A·B International, 1988
•