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Ultrastructural characterization of sensilla and microtrichia on the antenna of female Haematopota pandazisi (Diptera: Tabanidae)


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The haematophagous females of the cleg fly Haematopota pandazisi (Kröber) (Diptera: Tabanidae) are a common pest in areas inhabited by wild and domestic ungulates in southern Europe, North Africa and Anatolia. A morphological investigation by scanning electron microscopy (SEM) was carried out for the first time on the antennae of females of H. pandazisi, with special attention to the type and distribution of sensilla and microtrichia. The typical brachyceran antenna is divided into three regions: the scape, the pedicel and the flagellum, which is the longest of the three and is composed of four flagellomeres. The scape and pedicel are characterized by only one type of microtrichium and chaetic sensillum, whereas five types of microtrichia and sensilla were identified on the flagellum and classified according to shape and distribution. The sensilla are of the chaetic, clavate, basiconic, trichoid and coeloconic types; the latter with either a basiconic or grooved peg inside. The results obtained in this study were compared to those found in other species in the family Tabanidae and other Diptera, with special attention to haematophagous species.
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Ultrastructural characterization of sensilla
and microtrichia on the antenna of female Haematopota pandazisi
(Diptera: Tabanidae)
Marco Pezzi
&Chiara Scapoli
&Elisabetta Mamolini
&Marilena Leis
&Teresa Bonacci
&Daniel Whitmore
Stjepan Krčmar
&Marica Furini
&Sauro Giannerini
&Milvia Chicca
&Rosario Cultrera
&Michel J. Faucheux
Received: 18 October 2017 / Accepted: 11 January 2018
#Springer-Verlag GmbH Germany, part of Springer Nature 2018
The haematophagous females of the cleg fly Haematopota pandazisi (Kröber) (Diptera: Tabanidae) are a common pest in areas
inhabited by wild and domestic ungulates in southern Europe, North Africa and Anatolia. A morphological investigation by
scanning electron microscopy (SEM) was carried out for the first time on the antennae of females of H. pandazisi,withspecial
attention to the type and distribution of sensilla and microtrichia. The typical brachyceran antenna is divided into three regions:
the scape, the pedicel and the flagellum, which is the longest of the three and is composed of four flagellomeres. The scape and
pedicel are characterized by only one type of microtrichium and chaetic sensillum, whereas five types of microtrichia and sensilla
were identified on the flagellum and classified according to shape and distribution. The sensilla are of the chaetic, clavate,
basiconic, trichoid and coeloconic types; the latter with either a basiconic or grooved peg inside. The results obtained in this study
were compared to those found in other species in the family Tabanidae and other Diptera, with special attention to
haematophagous species.
Keywords Antenna .Cleg .Haematopota pandazisi .Microtrichia .SEM .Sensilla
The family Tabanidae includes about 4406 species and sub-
species belonging to 137 genera worldwide (Roskov et al.
2013), some of which are of medical and veterinary impor-
tance (Mullens 2009). The family is divided into three sub-
families: Pangoniinae, Chrysopsinae and Tabaninae. The spe-
cies of the subfamily Pangoniinae are also called long-tongued
horse fliesbecause of their elongated and thin proboscis, and
have a relevant role as pollinators. Those of the subfamily
Chrysopsinae, known as deer flies, have brilliantly coloured
eyes and long antennae. The subfamily Tabaninae, known as
horse flies, has the highest species diversity within the family.
The species of the genus Haematopota, commonly known as
clegs, belong to the subfamily Tabaninae (Chainey 1993;
Morita et al. 2016).
Feeding habits in adult Tabanidae differ according to sex:
females feed on blood and males on nectar. Female tabanids
are therefore relevant vectors of many diseases due to the
accumulation of microorganisms in their mouthparts, salivary
*Marco Pezzi
Department of Life Sciences and Biotechnology, University of
Ferrara, Via Luigi Borsari 46, 44121 Ferrara, Italy
Department of Biology, Ecology and Earth Science, University of
Calabria, Via P. Bucci, 87036, Arcavacata di Rende, Cosenza, Italy
Department of Life Sciences, Natural History Museum, Cromwell
Road, London SW7 5BD, UK
Department of Biology, Josip Juraj Strossmayer University of Osijek,
Cara Hadrijana 8/A, HR-31000 Osijek, Croatia
UNIFAUNA (cultural and scientific association), Via di Montepaldi,
12, 50026, San Casciano in Val di Pesa, Firenze, Italy
Department of Medical Sciences, Section of Dermatology and
Infectious Diseases,University of Ferrara, Via Fossato di Mortara 64/
B, 44121 Ferrara, Italy
Laboratoire dEndocrinologie des Insectes Sociaux, Université de
Nantes, 2 rue de la Houssinière, B. P. 92208, F-44322 Nantes Cedex
03, France
Parasitology Research
glands and/or on their tarsi, which they transfer to their hosts
during feeding (Lessard et al. 2013). Their piercing proboscis
allows them to feed on vertebrates, including cattle and
humans (Krenn and Aspöck 2012). The genera
Haematopota,Tabanus, and Hybomitra are important pests
in the Old World (Mullens 2009). All species of
Haematopota are terrestrial, with edaphic larvae able todevel-
op on humus and colonize habitats distant from water bodies
(Di Luca 2012). The genus contains 28 species in Europe
(Chvála 2004). Haematopota pandazisi (Kröber) is distribut-
ed in southern Europe, North Africa and Anatolia (Chvála
et al. 1972; Chvála 2004), and has been reported from the
Italian mainland and Sicily (Di Girolamo et al. 1995; Chvála
2004). It is a common pest in areas inhabited by wild and
domestic ungulates, including cattle farms and stables
(Rivosecchi et al. 1986; Trentini 2001), and may also bite
humans (Krčmar and Marić2006).
Ultrastructural studies on the antennae of species of
Tabanidae are few and include descriptions of chaetic,
basiconic, coeloconic and trichoid sensilla (Elizarov and
Chaika 1977; Faucheux 1981;Parasharetal.1994;Ivanov
2007), whose functions range from mechanotactile to olfacto-
ry (Elizarov and Chaika 1977; Parashar et al. 1994;Ivanov
2007). Previous ultrastructural studies on the antennae of spe-
cies of the genus Haematopota were limited and scarcely de-
tailed (Elizarov and Chaika 1977;Parasharetal.1994).
This paper provides the first scanning electron microscopy
investigation of the morphology of the antenna of the female
of H. pandazisi, including information on the type and distri-
bution of its sensilla and microtrichia. This detailed study on
antennal morphology and distribution of sensilla and
microtrichia could be relevant for further investigations on
sensorial activities related to the search for suitable hosts,
mates, and larviposition sites in the Tabanidae family. These
data could also be useful for taxonomic and phylogenetic
Materials and methods
The specimens used in this study were collected from July to
September 2016 in the rural areas around Podere Nappo,
Oasi Dynamo Società Agricola, Limestre (Pistoia province,
Italy) (44° 22.33N; 10° 4742.86E), at elevations of about
10001100 m. They were captured with an insect net in an
area densely populated by wild and domestic ungulates,
placed in plastic boxes and brought live to the Laboratory of
Urban Ecology, Medical and Veterinary Entomology of the
University of Ferrara. The insects were then anaesthetized
with CO
, individually placed in 1.5-ml plastic tubes and,
while still anaesthetized, killed in a freezer at 20 °C, where
they were stored. The specimens were morphologically iden-
tified as females of H. pandazisi under a Nikon SMZ 800
stereomicroscope (Nikon Instruments Europe, Amsterdam,
The Netherlands) and using the identification keys of Chvála
et al. (1972)andKrčmar et al. (2011).
Given the morphological similarity of this species to
Haematopota italica Meigen, a molecular analysis through
COI gene-based DNA barcoding (Hebert et al. 2003) was
carried out through the DNA Analysis Serviceof FEM2-
Ambiente s.r.l., University of Milan-Bicocca (Milan, Italy).
The results of DNA barcoding excluded the specimens from
belonging to H. italica, due to high genetic distances with
reference barcode sequences of this species. These analyses
also excluded possible similarity with nine other
Haematopota species with sequences deposited in the inter-
national genetic repository (
The DNA barcoding data therefore supported the
morphological identification of the species as H. pandazisi.
For scanning electron microscopy (SEM), 15 females were
fixed, postfixed and dehydrated using the methods described in
Pezzi et al. (2017). The method proposed by Khedre (1997)
was employed to visualize the inner parts of the antenna under
SEM. After dehydration, the samples were critical point dried
in a Balzers CPD 030 dryer (Leica Microsystems, Wetzlar,
Germany), mounted on stubs and coated with gold-palladium
using an Edwards S-150 sputter coater (HHV Ltd., Crawley,
UK). The SEM observations were conducted at the Electron
Microscopy Centre, University of Ferrara, with a Zeiss EVO 40
SEM (Zeiss, Milan, Italy). Morphometric measurements were
performed during SEM observations, using the software ZEISS
SmartSEm v.5.09.SP10 (Carl Zeiss Ltd., Oberkochen,
Germany). Measurements were expressed as an average with
standard deviation.
The terminology of the antennal segments follows Keil
(1999), who divides the antenna into the scape, the pedicel
and the flagellum, composed of several flagellomeres. The
terminology of sensilla and microtrichia follows McIver
(1982) and Khedre (1997).
The antenna of the female of H. pandazisi (total length 2.30 ±
0.05 × 10
μm) is composed of three segments, the scape, the
pedicel and the flagellum (Fig. 1a and inlay). The scape
(964.38 ± 31.71 μm long) is cylindrical with a thinner proxi-
mal region (Fig. 1b). Its surface is covered by short and thin
microtrichia with longitudinal grooves and a blunt tip (Fig. 1b,
c), and by numerous chaetic sensilla (83.13 ± 17.34 μmlong),
each composed of a long articulated bristle with longitudinal
grooves and a sharp tip (Fig. 1b, d). The pedicel (154.68 ±
10.89 μm long) is of a truncated conical shape with two distal
triangular processes, the first in a dorsal position (101.40 ±
7.53 μm long) and the second, much shorter, in a ventral
position (33.60 ± 4.82 μm long) (Fig. 1a, e). The surface of
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the pedicel is covered by microtrichia and chaetic sensilla
(107.63 ± 24.92 μm long), both morphologically similar to
those of the scape (Fig. 1e). The flagellum, the longest region
of the antenna (1.10 ± 0.03 × 10
μm), is composed of four
Fig. 1 Scanning electron micrographs of head offemale of Haematopota
pandazisi.aLateral view of right antenna. Inlay: female head capsule. b
Scape. cDetail of surface of scape, showing microtrichia. dDetail of base
of chaetic sensillum. eLateral view of pedicel, showing dorsal (arrow)
and ventral (arrowhead) processes. CSP, chaetic sensilla of pedicel; CSS,
chaetic sensilla of scape; FL, flagellum; H, head; MS, microtrichia of
scape; PE, pedicel; SC, scape
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flagellomeres, of which the first is the longest (Figs. 1a and
2a). The first flagellomere (768.98 ± 29.98 μm long) can be
divided intotwo regions according to microtrichia and sensilla
types (Fig. 2a). The proximal region (193.65 ± 15.31 μm
long) (Fig. 2b) has only two types of microtrichia: the first
type hair-like with longitudinal grooves, the second shorter
and smooth (Fig. 2c). The proximal and distal regions of the
flagellomere are separated by a crownof chaetic sensilla
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(69.71 ± 5.61 μm long) with the same morphology as those on
the scape and pedicel (Fig. 2a, b). These sensilla are also
scattered on the surface of the other flagellomeres (Fig. 2a)
and near the joints connecting the flagellomeres. The distal
region of the first flagellomere (549.86 ± 16.60 μm long)
(Fig. 2a) is characterized by three types of microtrichia (Fig.
2df), five types of sensilla (Figs. 2b and 3ai), and cuticle
perforations (Fig. 3bd, g). The microtrichia of the first type
cover the entire surface of the region and are of a flat, trian-
gular shape with longitudinal grooves and a sharp tip (Fig.
2d). Those of the second type are characterized by three tips
and longitudinal grooves (Fig. 2e). Those of the third type are
shorter, conical and with a rounded tip (Fig. 2f). These last two
types of microtrichia are scattered along the distal region of
the flagellomere. The sensilla of the distal region of the first
flagellomere are complex and include clavate, basiconic and
trichoid sensilla plus two different types of coeloconic sensil-
la. The clavate sensilla, each located within a low depression,
are club-shaped with a blunt tip (Fig. 3a). The basiconic sen-
silla, each located within a shallow depression, are all mor-
phologically similar and with rounded tips, but range in length
from 6.24 to 15.33 μm(Fig.3b). The trichoid sensilla, each
located within a shallow depression, are conical with a round-
ed tip (Fig. 3c). The coeloconic sensilla belong to two types
based on their general shape and inner peg. Those of the first
type are dome-shaped, with an oval opening at the top (Fig.
3d). Some perforations are visible on the dome (Fig. 3d).
When the flagellum is longitudinally sectioned, the coeloconic
sensillum shows a spherical invagination (Fig. 3e). When
opened, the coeloconic sensillum appears divided into two
spaces by a thickening. The upper space corresponds to the
outside dome and the lower space to the spherical invagina-
tion, which in turn contains a basiconic peg, off-centered and
with a blunt tip (Fig. 3f). The coeloconic sensillum of the
second type appears on the outside as a circular opening
surrounded by microtrichia, with the tip of a peg visible in
its center (Fig. 3g). When the flagellum is longitudinally
sectioned, this type of sensillum appears as a squat cylinder
(Fig. 3h) with a single internal cavity containing a centered
peg, deeply grooved, with a large conical base and blunt tip
(Fig. 3i).
The distribution of sensilla varies in the distal region of the
first flagellomere, with three different associations of sensilla
along the major axis of the flagellomere (Fig. 2a): an associ-
ation of clavate sensilla and both types of coeloconic sensilla,
from the base of the distal region to a distance of about 102.60
±7.92μm(Figs.2a and 4a); an association of basiconic and
trichoid sensilla from this limit to about 361.26 ± 16.64 μm
(Figs. 2a and 4b); and an association of basiconic sensilla and
coeloconic sensilla of the first type, with rare trichoid sensilla,
in the most apical part of the region (80.13 ± 3.79 μmlong)
(Figs. 2a and 4c).
The second, third and fourth flagellomeres are shorter than
the first (Figs. 1a and 2a), respectively 129.53 ± 14.31 μm,
110.13 ± 4.74 μm and 171.90 ± 8.14 μm. The second and
third flagellomeres are cylindrical while the fourth is conical
(Fig. 2a), and their entire surface is covered by microtrichia
similar to those found in the distal region of the first
flagellomere (Fig. 4d). Basiconic and trichoid sensilla as well
as coeloconic sensilla of both types are scattered throughout
their surface, whereas clavate sensilla are rare and restricted to
The present study is the first to describe the ultrastructural
morphology of the antenna of the female of H. pandazisi.
Morphological studies on the antennae of Tabanidae are lim-
ited and the antennae of only two species of Haematopota
have been described: Haematopota pluvialis L. (Smith 1919;
Elizarov and Chaika 1977)andHaematopota dissimilis
Ricardo (Parashar et al. 1994). Other tabanid genera for which
the antennae have been described are Atylotus,Chrysops,
Hybomitra, and Tabanus (Smith 1919;Lall1970; Elizarov
and Chaika 1977; Faucheux 1981; Parashar et al. 1994;
Ivanov 2007). The antennae of H. pandazisi are generally
similar to those of other species of the genus (Chvála et al.
1972). The antennae of females of this species are character-
ized by five types of sensilla: chaetic, clavate, coeloconic,
basiconic and trichoid. As in other species of Tabanidae, the
chaetic sensilla of H. pandazisi are articulated, with longitu-
dinal grooves and a sharp tip (Lall 1970; Elizarov and Chaika
1977; Faucheux 1981; Parashar et al. 1994; Ivanov 2007).
Similar chaetic sensilla have been described as sensilla with
a thick wall(Elizarov and Chaika 1977), or more recently as
trichoid sensilla(Ivanov 2007). The distribution of chaetic
sensilla on the scape and pedicel is also similar to that of other
Tab ani dae (Lall 1970; Elizarov and Chaika 1977; Faucheux
1981;Parasharetal.1994;Ivanov2007). As in H. pandazisi,
Fig. 2 Scanning electron micrographs of flagellum of female of
H. pandazisi.aLateral view of flagellum. Dashed lines highlight crown
of chaetic sensilla between proximal and distal regions of first
flagellomere. Rectangle outlines region enlarged in (b). Arrows indicate
chaetic sensilla on flagellomeres. bDetail of (a) showing boundary
between proximal and distal regions of first flagellomere, indicated by
dashed line. cHair-like grooved microtrichia and short smooth ones in
proximal region of first flagellomere. dFlat triangular microtrichia, found
on all flagellomeres except in proximal region of first. eMicrotrichia with
three tips, found on all flagellomeres except in proximal region of first. f
Conical microtrichia, found on all flagellomeres except in proximal
region of first. 1AS3AS, parts of distal region of first flagellomere,
characterized by different associations of sensilla; 1FL4FL,
flagellomeres; 1FLD, distal region of first flagellomere; 1FLP, proximal
region of first flagellomere; CM, conical microtrichia; CSF, chaetic
sensilla of flagellomeres; FM, flat triangular microtrichium; HM, hair-
like microtrichium; SM, short, smooth microtrichium; TM,
microtrichium with three tips. Other abbreviations as in Fig. 1
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the chaetic sensilla are found in the proximal part of the first
flagellomere in Hybomitra lasiophthalma (Macquart) and
Tabanus lineola Fabricius (Lall 1970), H. pluvialis and
Taba nus bro mi us L. (Elizarov and Chaika 1977). The chaetic
sensilla observed on the distal part of each flagellomere in
H. pandazisi have also been observed in Chrysops vittatus
Wiedemann, H. lasiophthalma,T. lineola (Lall 1970),
Chrysops relictus Meigen, H. pluvialis,T. bromius (Elizarov
and Chaika 1977), and Atylotus fulvus Meigen (Faucheux
1981). The chaetic sensilla form an encircling crownaround
the proximal region of the first flagellomere in H. pandazisi;
whereas in H. lasiophthalma,T. lineola (Lall 1970),
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H. pluvialis and T. bromius (Elizarov and Chaika 1977)they
are grouped together in one or two tufts. In H. lasiophthalma,
T. lineola (Lall 1970)andT. bromius they form a single tuft
near the dorsal process, while in H. pluvialis they form two
tufts: one dorsal and one ventral (Elizarov and Chaika 1977).
In other species such as H. dissimilis,Tabanus rubidus
Wiedemann, Tabanus striatus Fabricius, and Tabanus
subcinerascens Ricardo, the chaetic sensilla are apparently
confined to only the scape and pedicel. In these four species
a mechanotactile function of the chaetic sensilla has been sug-
gested (Parashar et al. 1994). The same has been suggested for
these sensilla in Hybomitra bimaculata (Macquart) and
Tabanus bovinus L. (Ivanov 2007), as well as in other
haematophagous Diptera belonging to the families
Ceratopogonidae (Blackwell et al. 1992) and Culicidae
(McIver 1982). The single chaetic sensillum located at the
tip of the antenna in both sexes of Culicoides impunctatus
Goetghebuer and Culicoides nubeculosus (Meigen) (Diptera:
Ceratopogonidae) is thought to have a general tactile function
for investigation of substrates and textures (Blackwell et al.
1992). In Simulium baffinense Twinn , Simulium
euryadminiculum Davies, Simulium rugglesi Nicholson and
Mickel, and Simulium venustum Say (Diptera: Simuliidae),
the arrangement of chaetic sensilla around the distal boundary
of the pedicel and the scape suggests the ability to detect the
direction and degree of bending of the pedicel and flagellum
(Mercer and McIver 1973). The similar distribution of chaetic
sensilla in H. pandazisi also suggests a role in detecting the
direction and degree of bending of the same structures.
In Simulium arcticum Malloch (Diptera: Simuliidae), a che-
moreceptive role has been proposed for the chaetic sensilla at the
antennal tip. These sensilla would perceive host epidermis during
biting site selection, and perhaps flower parts during nectar feed-
ing(Shippetal.1988). In H. pandazisi, the clavate sensilla are
each localized in a circular depression and are club-shaped with
blunt tips, similar to those classified as a type of basiconic sen-
sillum in H. dissimilis,T. rub idus ,T. stri atus and
T. subcinerascens by Parashar et al. (1994), and in
H. bimaculata and T. bovinus by Ivanov (2007). Clavate sensilla
are rather unusual in haematophagous Diptera. Those of
H. pandazisi are similar to those described in S. arcticum and
Haematobia irritans irritans (L.) (Diptera: Muscidae) (White
and Bay 1980; Shipp et al. 1988), and are classified as basiconic
sensilla in S. arcticum (Shipp et al. 1988). Clavate sensilla are
common in non-haematophagous Diptera and have been previ-
ously described in Anthomyiidae (Honda et al. 1983;Ross
1992), Calliphoridae (Fernandes et al. 2004; Zhang et al.
2014), Fanniidae (Wang et al. 2012; Zhang et al. 2013b),
Muscidae (Been et al. 1988; Smallegange et al. 2008;Zhang
et al. 2013a;Wangetal.2014), Oestridae (Hunter and
Adserballe 1996; Zhang et al. 2012;Liuetal.2015),
Sarcophagidae (Khedre 1997; Pezzi et al. 2016),
Scathophagidae (Liu et al. 2016), and Tephritidae (Giannakakis
and Fletcher 1985;Levinsonetal.1987;Mayoetal.1987;Lee
et al. 1994;Arzuffietal.2008; Castrejón-Gómez and Rojas
2009; Bisotto-de-Oliveira et al. 2011). Sensilla of this type are
located in the proximal region of the first flagellomere in
H. pandazisi and scattered at the base of the other flagellomeres.
This condition is in part similar to that found in other Tabanidae,
where sensilla with a clavate shape are distributed on the proxi-
mal part of the first flagellomere but are missing on the other
flagellomeres (Parashar et al. 1994; Ivanov 2007). An olfactory
role has been proposed for these sensilla, which are also thought
to possess hygrosensitive cells (Lewis 1972), in haematophagous
Diptera such as S. arcticum (Shipp et al. 1988)andStomoxys
calcitrans L. (Muscidae) (Tangtrakulwanich et al. 2011). An
olfactory role for clavate sensilla has also been suggested in five
non-haematophagous species of the family Anthomyiidae
(Honda et al. 1983; Ross 1992).
In H. pandazisi there are two types of coeloconic sensilla.
The first type is dome-shaped with an oval opening and con-
tains an off-centered basiconic peg, while the second type has
a circular opening containing a centered and grooved peg. The
presence of two types of coeloconic sensilla and their detailed
morphology has never been previously documented for the
antennae of Tabanidae.
In Chrysops caecutiens (L.), C. relictus,Chrysops rufipes
Meigen, H. pluvialis,Hybomitra montana (Meigen), T.
bromius (Smith 1919; Elizarov and Chaika 1977), A. fulvus
(Faucheux 1981), H. bimaculata and T. bovin u s (Ivanov
2007), coeloconic sensilla have been observed but no descrip-
tion of their outer and inner morphology has been provided. In
other documented species of Tabanidae including
H. dissimilis,T. rubidus,T. striatus and T. subcinerascens
(Parashar et al. 1994), no coeloconic sensilla have been re-
ported. The distribution of these sensilla in H. pandazisi is
similar to that reported for A. fulvus (Faucheux 1981) and
H. pluvialis (Elizarov and Chaika 1977). Two types of
Fig. 3 Scanning electron micrographs of flagellum detail of female of
H. pandazisi.aClavate sensillum. bBasiconic sensillum. Arrows
indicate cuticle perforations. cTrichoid sensilla. Arrows indicate cuticle
perforations. dOutside surface of coeloconic sensillum of first type,
dome-shaped and with oval opening (asterisk). Arrows indicate cuticle
perforations. eCoeloconic sensillum of first type. Asterisk indicates inner
surface of flagellum and arrow indicates cavity of peg connected with
antennal cavity. fCoeloconic sensillum of first type, opened to show
basiconic peg. Dashed line highlights presence of two spaces inside
sensillum. Arrow indicates oval opening of sensillum. gOutside surface
of coeloconic sensillum of second type, with circular opening. White
arrow indicates grooved peg and black arrows indicate cuticle
perforations. hCoeloconic sensillum of second type. Asterisk indicates
inner surface of flagellum and arrow indicates cavity of peg connected
with antennal cavity. iCoeloconic sensillum of second type, opened to
show grooved peg. Diamond and arrow respectively indicate inside and
opening of sensillum. BPC, basiconic peg of coeloconic sensillum of first
type; BS, basiconic sensillum; CFT, coeloconic sensillum of first type;
CL, clavate sensillum; CST, coeloconic sensillum of second type; GPC,
grooved peg of coeloconic sensillum of second type; TS, trichoid sensilla
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Fig. 4 Scanning electron micrographs of first and second flagellomere
details of female of H. pandazisi.aDetail of distal region of first
flagellomere showing first association of sensilla (1AS, Fig. 2a),
consisting of clavate sensilla and two types of coeloconic sensilla. b
Detail of distal region of first flagellomere showing second association
of sensilla (2AS, Fig. 2a), consisting of basiconic and trichoid sensilla. c
Detail of distal region of first flagellomere showing third association of
sensilla (3AS, Fig. 2a), consisting of basiconic sensilla and coeloconic
sensilla of first type, with rare trichoid sensilla. dVariety of microtrichia
and sensilla of second flagellomere. Abbreviations as in Figs. 2and 3
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coeloconic sensilla have been described in other
haematophagous Diptera belonging to the subfamily
Anophelinae (Diptera: Culicidae) (Boo 1980; Pitts and
Zwiebel 2006;Hempolchometal.2017;Taaietal.2017), in
Lutzomyia longipalpis (Lutz and Neiva) (Diptera:
Psychodidae) (Fernandes et al. 2008), and in H. irritans
irritans (White and Bay 1980). Coeloconic sensilla bearing
a single peg without longitudinal grooves have also been de-
scribed in Anopheles maculipennis Meigen (Ismail 1964)and
Anopheles stephensi Liston (Diptera: Culicidae) (Boo and
McIver 1975;Boo1980). Coeloconic sensilla with a single
grooved peg are common in families of haematophagous
Diptera such as Ceratopogonidae (Chu-Wang et al. 1975;
Blackwell et al. 1992; Alexandre-Pires et al. 2010; Isberg
et al. 2013; Urbanek et al. 2014), Culicidae (Ismail 1964;
Boo and McIver 1976;Boo1980;PittsandZwiebel2006;
Hempolchom et al. 2017; Taai et al. 2017), Psychodidae
(Fernandes et al. 2008) and Hippoboscidae (Zhang et al.
2015). Concerning these sensilla, a thermoreception role has
been proposed in Aedes aegypti L. (Diptera: Culicidae), and a
thermoreception (Boo and McIver 1975) and an olfactory one
(Boo and McIver 1976)inA. stephensi. Olfactory and
hygroreceptor roles have also been suggested in Culicoides
furens (Poey) (Diptera: Ceratopogonidae) by Chu-Wang
et al. (1975).
ThebasiconicsensillaofH. pandazisi, characterized by
having blunt tips and being located within shallow depres-
sions on the flagellum, are similar to those observed in other
Tabanidae such as C. caecutiens,C. relictus,C. rufipes,
H. pluvialis,H. montana,T. bromius (Elizarov and Chaika
1977), and A. fulvus (Faucheux 1981),andtoafourthtype
of basiconic sensillum seen in H. dissimilis,T. rubidus,
T. striatus,andT. subcinerascens (Parashar et al. 1994), as
well as a fifth type of basiconic sensillum in H. maculata
and T. bovinus (Ivanov 2007). In two other species of
Haematopota,H. dissimilis and H. pluvialis, this type of
sensillum was apparently found only on the first
flagellomere (Elizarov and Chaika 1977;Parasharetal.
1994). However, in other Tabanidae such as C. relictus
(Elizarov and Chaika 1977), A. fulvus (Faucheux 1981),
H. maculata,andT. bovinus (Ivanov 2007), these sensilla
were found on all flagellomeres. Basiconic sensilla are
thought to play an olfactory role in Tabanidae (Elizarov
and Chaika 1977; Parashar et al. 1994). As with clavate
sensilla, the basiconic sensilla are thought to play an olfac-
tory role in the haematophagous species S. arcticum (Shipp
et al. 1988)andS. calcitrans (Tangtrakulwanich et al.
2011), whereas a hygrosensitive role has also been reported
for S. calcitrans (Lewis 1972). An olfactory role of these
sensilla has also been proposed in non-haematophagous
Diptera, including Anthomyiidae (Honda et al. 1983),
Drosophilidae (Clyne et al. 1997), Phoridae (Lu et al.
2012), Stratiomyidae (Faucheux and Mason 2001),
Sarcophagidae (Sukontason et al. 2004), Muscidae
(Sukontason et al. 2004,2007) and Calliphoridae
(Sukontason et al. 2004;Horeetal.2017).
In H. pandazisi, the trichoid sensilla are conical with a round-
ed tip and each located within a shallow depression. Trichoid
sensilla with similar morphology have been reported in
H. dissimilis,T. rubi d us,T. striatus,T. subcinerascens (Parashar
et al. 1994), H. bimaculata and T. bovinus (Ivanov 2007), al-
though in these species they were described as basiconic sensilla.
Trichoid sensilla that are morphologically similar to those of
H. pandazisi have never been reported in other haematophagous
Diptera besides Tabanidae, but they have been found in non-
haematophagous species such as Bactrocera tryoni (Froggatt)
(Tephritidae) (Giannakakis and Fletcher 1985), Hydrotaea
irritans (Fallén) (Muscidae) (Been et al. 1988), Bactrocera
dorsalis (Hendel) (Tephritidae) (Lee et al. 1994), Pselaphomyia
nigripennis (Bigot) (Stratiomyidae) (Faucheux and Mason 2000)
and Pseudacteon sp. (Phoridae) (Lu et al. 2012). In H. irritans,
these sensilla have been described as basiconic (Been et al.
1988). In Tabanidae, an olfactory role has been proposed for
trichoid sensilla (Parashar et al. 1994). Investigations on the role
of these sensilla in haematophagous Diptera have been conduct-
ed mainly in Culicidae and an olfactory role was clearly demon-
strated, especially in relation to detection of hosts and oviposition
sites (Qiu et al. 2006; Hill et al. 2009; Siju et al. 2010). An
olfactory role for trichoid sensilla has also been proposed in other
haematophagous species such as Boophthora erythrocephala
(De Geer) (Diptera: Simuliidae) (Elizarov and Chaika 1975),
but in S. calcitrans (Lewis 1972)theyhavebeenreportedas
chemoreceptors. The same role has been proposed in non-
haematophagous families such as Anthomyiidae (Ross 1992),
Oestridae (Hunter and Adserballe 1996), Psilidae (Ross 1992)
and Tephritidae, where a role in the perception of sexual phero-
mone and host plant volatiles has also been suggested (Levinson
et al. 1987; Arzuffi et al. 2008).
Other common structures observed on the antennae of
H. pandazisi are the microtrichia. The present study includes
the first detailed description of their morphology and distribu-
tion in a species of Tabanidae.
In Tabanidae, microtrichia are generally distributed on all
regions of the antenna (Elizarov and Chaika 1977;Parashar
et al. 1994; Ivanov 2007), but in H. dissimilis,T. rubidus,
T. striatus and T. subcinerascens they have been indicated as
sensilla stellate(Parashar et al. 1994). A total of six different
types of microtrichia have been found in H. pandazisi accord-
ing to their location and morphology. Those of the first type,
distributed on the scape and pedicel, are short and character-
ized by longitudinal grooves and a blunt tip, and are similar to
those described in H. bimaculata and T. bovinus (Ivanov
2007). Those of the second and third types, distributed on
the proximal region of the first flagellomere in H. pandazisi,
are hair-like with longitudinal grooves and short and smooth,
respectively. Microtrichia of a similar shape had never been
Parasitol Res
previously described in Tabanidae and their distribution in the
proximal region of the first flagellomere is also unusual since
this region is devoid of sensilla. A similar distribution has
been apparently observed only in C. vittatus (Lall 1970),
C. relictus,andH. pluvialis (Elizarov and Chaika 1977), and
could be related to the mechanoreceptive role of the chaetic
sensilla of the pedicel and of the crown on the first
The last three types of microtrichia found on the antennae
of females of H. pandazisi are distributed on the distal part of
the first flagellomere and on all other flagellomeres. The first
of these additional types has a flat triangular shape with lon-
gitudinal grooves and a sharp tip, and is similar to microtrichia
reported in H. bimaculata and T. bovinus (Ivanov 2007). The
remaining two types of microtrichia are of a tricuspid and a
conical shape, respectively, and had never been previously
described in any species of Tabanidae.
The high morphological diversity of sensilla and
microtrichia on the antennae of females of H. pandazisi shows
the relevance of these structures in the sensorial perception of
this haematophagous species as well as in other Diptera.
Investigations of the sensorial structures in Tabanidae may
establish a base for electrophysiological and molecular studies
on sensorial activities involved in the search for hosts, mates,
and larviposition sites,as well as for applications in the control
of infesting populations, such as developing attractants for
traps or repellents for animal and human protection. Finally,
the ultrastructural details of these antennal structures may con-
tribute key data to taxonomic and phylogenetic studies on this
important group of Diptera.
Acknowledgments The authors owe thanks to Dr. Cristina Rinaldi, Dr.
Maria Silvia Bellotti, and Dr. Egizia Zironi (University Library System,
Ferrara, Italy) for their valuable help in providing references. Thanks are
also due to Miss Giulia Santalmasi (Dynamo Camp, Limestre, Pistoia,
Italy). The manuscript is dedicated to the loving memory of Mr. Simeone
Pezzi Ancarani.
Funding information This study was funded by Consorzio Futuro in
Ricerca(Ferrara, Italy), code n. LEIS40/17, assigned to Marilena Leis.
Compliance with ethical standards
Conflict of interest The authors declare that they have no conflict of
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... A chemoreceptive role has been proposed for the sensilla chaetica at the antennal tip of S. arcticum (Shipp et al., 1988). These sensilla would come into contact with the host epidermis while selected a biting site, and perhaps flower parts during nectar feeding (Pezzi et al., 2018). ...
... Subtype I has inconspicuous pores, while the other three subtypes have dense pitting of the cuticle. Subtypes III and IV are located within shallow depressions on all flagellomeres, and are similar to those observed in other studies (Pezzi et al., 2018). However, measurements of subtype IV were not possible in this study, as their bases are invisible. ...
... One type of sensillum coeloconicum was found in this study, whereas two types were identified in An. minimus and An. harrisoni (Diptera: Culicidae) , Haematopota pandazisi (Diptera: Tabanidae) (Pezzi et al., 2018), and Lutzomyia longipalpis (Diptera: Psychodidae) (Fernandes et al., 2008). Apart from a chemosensory function (Lui et al., 2021), this sensillum type has proven to be sensitive to temperature (thermoreceptive) and humidity (hygroreceptive) Pezzi et al., 2018). ...
Antennae and maxillary palpi are the most important sensory organs involved in the behaviors of black flies. The ultrastructure of sensilla on these sensory appendages of two human-biting black fly species, Similium nigrogilvum and Simulium umphangense, was studied for the first time. Wild adult females of both species were collected in Umphang District, Tak Province, western Thailand. The morphology and distribution of sensilla were examined using scanning electron microscopy. Overall, the morphology of the antennae and maxillary palpi and distribution of sensilla are similar in the two species. Four major types of sensilla were found on the antennae of both species: sensilla basiconica (three subtypes), coeloconica, chaetica (four subtypes), and trichodea. However, sensilla basiconica subtype IV are only present on the antennal surface of S. nigrogilvum. Sensilla trichodea are the most abundant among the four types of sensilla that occur on the antennae of both species. Significant differences in the length of the antennae (scape and flagellomere IX), length of the maxillary palpi (whole and palpal segments I, III, IV and V), and the length and basal width of four sensilla types (trichodea, chaetica, basiconica, and coeloconica) were found. In addition, two types of sensilla were observed on the maxillary palpi: sensilla chaetica (three subtypes) and bulb-shaped sensilla. Differences were observed in the numbers of bulb-shaped sensilla in the sensory vesicles of S. nigrogilvum and S. umphangense. The findings are compared with the sensilla of other insects, and the probable functions of each sensillum type are discussed. The anatomical data on sensory organs derived from this study will help to better understand black fly behavior.
... The olfactory sensilla is characterized as numerous pores on the cuticle, which permit the entry of the semiochemical contacting with the receptors on the dendrite membrane. Even though the sensillum structures have been well studied in a variety of insect species [6][7][8], previous studies have not reported the fine ultrastructure of the sensilla on B. dorsalis antennae and maxillary palps, despite the economic and agricultural importance of this pest. ...
... It was found that the antennae and maxillary palps were covered with numerous olfactory sensilla (i.e., ST, SB, and SCo) and non-olfactory sensilla (i.e., SCh and MI). The types, abundance, and distribution of these sensilla are similar to that observed from other Dipteran species, such as Anastrepha serpentine [16], Haematopota pandazisi [8], and B. zonata [17]. These findings were confirmed by previous research [18], except the ST, which we classified into olfactory sensilla based on the multi pores on the surface of the sensilla, observed with the FESEM. ...
... The SB are mainly distributed on the antennae and maxillary palps, which have been reported in various species such as Hydrotaea chalcogasten [21], Toxotrypana Curvicauda [22], Pseudacteon tricuspis [24], and H. pandazisi [8]. They are identified as olfactory sensilla with ultrastructure characteristics of numerous nano pores present on the surface. ...
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The sensilla on the antennae and maxillary palps are the most important olfactory organs, via which the insect can perceive the semiochemicals to adjust their host seeking and oviposition behaviors. The oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), is a major agricultural quarantine pest infesting more than 250 different fruits and vegetables. However, the sensilla involved in olfaction have not been well documented even though a variety of control practices based on chemical communication have already been developed. In this study, the ultrastructure of the sensilla, especially the olfactory sensilla on the antennae and maxillary palps of both males and females, were investigated with field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Three types of olfactory sensillum types including trichodea, basiconica, and coeloconica, and two non-olfactory sensilla including both chaetica and microtrichia, were observed. Each of these three types of olfactory sensilla on the antennae of B. dorsalis were further classified into two subtypes according to the morphology and number of receptor cells. For the first time, the pores on the sensilla trichodea and basiconica cuticular wall were observed in this species, suggesting they are involved in semiochemical perception. This study provides new information on B. dorsalis olfaction, which can be connected to other molecular, genetic, and behavioral research to construct an integral olfactory system model for this species.
... In particular, in H. equina the microtrichia are present also on the internal surface of the antennal fossa, lending support to this hypothesized role. Recently, six types of microtrichia, including branched ones, have been detected also on the flagellum of the tabanid fly Haematopota pandazisi (Krober, 1936) by Pezzi et al. [35], who postulated the role of these structures, together with different kinds of sensilla, in the sensory perception. ...
... Although there are a few electrophysiological studies about the role played by basiconic sensilla, it is known that they are mainly involved in odour detection due to the presence of many pores on the external wall [55]. The multiporous basiconic sensilla occurring on L. fortisetosa differ from those described in other dipterans [34,35,54,56], since the ultrastructure shows a reduction in the presence of the wall pores, which occur only in the distal half of the shaft. The limited number of pores on the basiconic walls could be due to the perception of the host odours which is activated just when the parasite is approaching the host at short-medium distances. ...
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Lipoptena cervi (Linnaeus), Lipoptena fortisetosa Maa, Hippobosca equina Linnaeus, and Pseudolynchia canariensis (Macquart) are hematophagous ectoparasites that infest different animal species and occasionally bite humans. Hosts are located by a complex process involving different kinds of stimuli perceived mainly by specific sensory structures on the antennae, which are the essential olfactory organs. General antennal morphology, together with distribution and ultrastructure of sensilla, have been studied in detail with scanning and transmission electron microscopy approaches. Observations have revealed some common features among the four studied hippoboscids: (a) typical concealment of the flagellum inside the other two segments; (b) characteristic trabecular surface of the flagellum; (c) peculiar external microtrichia; (d) presence on the flagellum of basiconic sensilla and grooved peg coeloconic sensilla; (e) unarticulated arista. The ultrastructure of L. fortisetosa revealed that microtrichia and the flagellar reticulated cuticle are not innervated. Different roles have been hypothesized for the described antennal structures. Microtrichia and the reticulated cuticle could convey volatile compounds towards the flagellar sensory area. Peculiar sensory neurons characterize the unarticulated arista which could be able to detect temperature variations. Coeloconic sensilla could be involved in thermoreception, hygroreception, and carbon dioxide reception at long distances, while the poorly porous basiconic sensilla could play a role in the host odour perception at medium–short distances.
... In insects, antennae have been identified as the main sensory organs involved in chemoreception, mechanoreception, thermoreception, and hygroreception, enabling the perception of various environmental signals, such as dispersed odoriferous molecules, temperature, and humidity (Hallberg, 1982;Steinbrecht, 1996;Liang and Fletcher, 2002;Bawin et al., 2017;Li et al., 2018;Pezzi et al., 2018). Antennae possess various sensilla, specialized components of the cuticular surface, which display diverse olfactory functions in life behaviors, including searching for food, habitat, and oviposition sites, or locating conspecifics for mating (Setzu et al., 2011;Ma et al., 2017). ...
The gall midge Gephyraulus lycantha (Diptera: Cecidomyiidae) is a serious gall-forming pest that causes devastating damage in the wolfberry, Lycium barbarum (Solanaceae) in Northwest China. In the present study, the external morphology and ultrastructure of the antennae and the antennal sensilla of G. lycantha were examined by scanning electron microscopy. The results show that the moniliform antenna of G. lycantha consisted of a scape, pedicel, and flagellum, and exhibited obvious sexual dimorphism. The male antennae were significantly longer than those of females. Moreover, male flagellomeres were spheroidal nodes separated by slender internodes, whereas those of females were cylindrical with no obvious internodes. There were sex and individual differences in antennal segment number. Male antennae had 10 − 16 flagellomeres, most of which had 15, while female antennae consisted of 8 − 14 flagellomeres, most of which had 12. Moreover, a pair of antennae in the same individual had different numbers of flagellomeres. Four types of sensilla were observed along the surface of the antennae, including sensilla chaetica, sensilla trichodea, sensilla coeloconica, and sensilla circumfila. Among the types of sensilla, sensilla chaetica were the longest and most prominent sensilla discovered on the antennal flagellum in both sexes. Sensilla trichodea were widely distributed over the antennal surface, including the scape, pedicel, and flagellum. Sensilla coeloconica were categorized into four subtypes: sensilla coeloconica Ⅰ, sensilla coeloconica Ⅱ, sensilla coeloconica Ⅲ, and sensilla coeloconica IV; however, sensilla coeloconica IV was absent in females. Sensilla circumfila were found only on cecidomyiidae insect antennae and were attached to the surface by a series of stalks, forming loops around each flagellomere. The numbers of all four types of sensilla on the male antennal windward side were significantly higher than those on the leeward side. The probable biological functions of these sensilla were discussed herein based on their morphology and ultrastructure. These results provide an important basis for further research on chemical communication and strategies for the control of G. lycantha, and it will be able to serve future group Taxonomy studies (species of cecidomyiidae), providing new taxonomic characters (general ultrastructural morphology, number of sensilla and antennal segments, distribution of different types of setae, types and subtypes sensilla), which varies between species and subspecies.
... The morphological and physiological characterization of these sensilla have been fundamental components of this research. Such studies have been done on species in the orders Diptera (Hempolchom et al., 2017;Pezzi et al., 2018), Hymenoptera Zhou et al., 2015), Coleoptera (Ren et al., 2014;Vera and Bergmann, 2018), and many species of Lepidoptera, considered important agricultural pests, such as Plutella xylostella L. (Lepidoptera: Plutellidae) (Yan et al., 2017), Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) (Diongue et al., 2013), and Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) (Seada, 2015). The characterization of their sensilla may help future studies to understand the physiological mechanisms whereby the chemical compounds of particular plants have repellent or attractive effects on such pests, as well as how these species detect their own sexual pheromones. ...
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Insects have several types of sensilla, the characterization of which has been fundamental to understanding the mechanisms of sensory perception in different species. This study aimed to describe the ultrastructure of the sensilla present on the antennae of Alabama argillacea (Hübner, 1823) (Lepidoptera: Erebidae), an important pest of cotton (Gossypium hirsutum L.) crops, as well as their possible variation between sexes. To do this, the antennae of males and females of A. argillacea were analyzed using scanning electron microscopy. Sensilla morphometry was assessed using photomicrographs, from which the lengths and basal and apical diameters of sensilla were measured using the ImageJ program. Seven types of sensilla were identified on the antennae of A. argillacea: sensilla trichodea, sensilla chaetica, sensilla auricillica, sensilla coeloconica, sensilla styloconica, sensilla basiconica, and sensilla Böhm bristles. Differences between the sensilla of males and females were found in their lengths and basal diameters in the distal and proximal regions. This suggests that sensilla functionality may not only vary from one species to another, but also between sexes within the same species. Thus, further transmission electron microscopy and single sensillum recording studies may provide more detailed information on the sensilla of A. argillacea and their functions.
Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae) has a great capacity to destroy stored grain worldwide. We report on the sensilla on the antennal funiculus of S. zeamais, using classical anatomical methods and scanning electron microscopy to obtain a detailed database of the antennal sensilla for each sex. The antenna is composed of eight antennomeres. Average antennal length is 781.58±20.64 µm for males and 808.91±11.80 µmfor females. Six types and subtypes of sensilla were identified on the funiculus: squamiform, basiconic (2 subtypes), chaetic (2 subtypes), and coeloconic. Sensilla squamiformia are distributed evenly but in few numbers on male and female antennomeres. Sensilla basiconica can be divided into subtypes, SB1 and SB2, according to the shape of the cone. Both subtypes occur on the last antennomere of the flagellum and there are fewer SB2 than SB1. Sensilla chaetica appear in the same position as sensilla basiconica and have two subtypes, SC1 and SC2. Significant differences were not found in the types of sensilla on the antennae of the two sexes, but a difference was found in the number of sensilla.
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Background Species of the Anopheles minimus complex are considered to be the primary vectors of malaria in South and Southeast Asia. Two species of the complex, Anopheles minimus and Anopheles harrisoni, occur in Thailand. They are sympatric and difficult to accurately distinguish based on morphological characters. The aim of this study was to investigate the potential of antennal sensory organs to distinguish these two species. Additionally, we investigated their ability to mate in cages of different sizes, as well as the possible mechanism(s) that evokes stenogamous behavior. Methods Large sensilla coeloconica present on the antennae of females of An. minimus and An. harrisoni were counted under a conventional light microscope and various types of antennal sensilla were examined under a scanning electron microscope (SEM). Determinations of mating ability were carried out in 20 and 30 cm3 cages with a density resting surface (DRS) of 7.2. The insemination rate, frequency of clasper (gonocoxopodite) movement of the male genitalia during induced copulation and duration of mating of the two species were compared. ResultsThe mean numbers of large sensilla coeloconica on antennal flagellomeres 1–8 and the mean number of large sensilla coeloconica on each flagellum in An. minimus (26.25) and An. harrisoni (31.98) were significantly different. Females of both species bear five types of antennal sensilla: chaetica, trichodea, basiconica, coeloconica and ampullacea. Marked differences in the structure of the large sensilla coeloconica were observed between the two species. Furthermore, only An. minimus could copulate naturally in the small cages. The frequency of clasper movement in the stenogamous An. minimus was significantly higher than in An. harrisoni, but there was no difference in the duration of mating. Conclusions To our knowledge, this study is the first to examine and discover the usefulness of large sensilla coeloconica on the antennae of females and the frequency of clasper movement in males for distinguishing the sibling species An. minimus and An. harrisoni. The discovery provides an effective and relatively inexpensive method for their identification. Additionally, the greater frequency of clasper movement of An. minimus might influence its ability to mate in small spaces.
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Antennal sensilla were first investigated in the eight medically and veterinary important Anopheles mosquito species (Anopheles argyropus, Anopheles crawfordi, Anopheles nigerrimus, Anopheles nitidus, Anopheles paraliae (= Anopheles lesteri), Anopheles peditaeniatus, Anopheles pursati, and Anopheles sinensis) of the Hyrcanus Group in Thailand, using scanning electron microscopy (SEM). Four types of sensilla, including sensilla chaetica (large and small), sensilla trichodea (sharp- and blunt-tipped), sensilla basiconica or grooved pegs (types I, II, and III), and sensilla coeloconica (large and small), were observed on the female antennae of the eight species. The greatest number of sensilla found along the flagellum of all the Anopheles species consisted of sensilla trichodea. Grooved pegs type II were not found on the antennae of An. peditaeniatus. Interestingly, clusters of 10–15 grooved pegs type III, with blunt-tipped and unevenly grooved-lengthwise sensilla, and a sunken group of 7–12 grooved pegs type III, with slightly curved and point-tipped sensilla, were found distally on flagellomeres 3–7 of An. argyropus and An. peditaeniatus, respectively. In addition, the key for species identification, based on fine structure and morphometrics of antennal sensilla among the eight species, was constructed and differentiated successfully. However, in order to focus intensively on the exact function of these sensilla, further electrophysiological study is needed in understanding their significant role in mosquito behavior, especially when these insects seek hosts for transmitting pathogens to humans.
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Scathophaga stercoraria (Linnaeus, 1758) is a well-established insect model species involved in numerous investigations on behavior, biology, phylogeny, genetics and evolution. The antennal sensilla of S. Stercoraria are examined via scanning electron microscopy in order to emphasize their importance on taxonomy and phylogeny. On antennal scape and pedicel, both microtrichiae and several sharp-tipped mechanoreceptors are observed, while another two structures, setiferous plaques and pedicellar button, are also detected on antennal pedicel. One type of sensory pit and four types of antennal sensilla, including trichoid sensilla, basiconic sensilla, coeloconic sensilla and clavate sensilla, are observed on antennal funiculus. Similarity and disparity of setiferous plaques among different calyptrate groups are analyzed in terms of phylogeny. The phylogenetic results supported by morphology of setiferous plaques strongly accord with the cladistic relations based on known molecular tree, implying the potential taxonomic and phylogenetic implications of the plaques in Calyptratae.
Blow flies (Diptera: Calliphoridae) are one of the foremost organisms amongst forensic insects to colonize corpses shortly after death, thus are of immense importance in the domain of forensic entomology. The blow fly Hemipyrellia ligurriens (Wiedemann, 1830) (Diptera: Calliphoridae) is considered as a forensically important fly species globally and is also known for its medical and veterinary importance. In the present study, we report for the first time scanning electron microscopic studies on the morphology of sensilla of antenna of adult male and female of H. ligurriens is with profound importance in better understanding of the insect morphology from forensic entomological perspective, and also could aid in proper identification of the species from other calliphorid flies. The structural peculiarities observed in the (i) antenna of H. ligurriens with three segments- scape, pedicel and flagellum with dorso-laterally placed arista (ii) densely covered microtrichia and most abundant trichoid sensilla identified on the antenna (iii) observation of only one type of sensilla, chaetic sensilla (ChI) on the scape (iv) two types of chaetic sensilla (ChI and ChII) and styloconic sensilla on the pedicel (v) the flagellum with three types of sensilla- trichoid, basiconic and coeloconic sensilla (vi) Basiconic sensilla with multiporous surfaces with characteristic olfactory function. Moderate sexual dimorphism in the width of the flagellum, the females with wider flagella than the males, bear significance to the fact that they bear more multi-porous sensilla than the males, thus suffice their need to detect oviposition sites. Significant difference was observed in the length and width of coeloconic sensilla between the two sexes, the females showed bigger coeloconic sensilla, suggesting their function in oviposition site detection and successful colonization in corpses.
The black soldier fly, Hermetia illucens (L.) (Diptera: Stratiomyidae), is a relevant species in waste and pest management, but is also of forensic and medical importance. A scanning electron microscopy (SEM) investigation of the antennae of both sexes of H. illucens is presented here for the first time. The antenna is composed of three regions: the scape, the pedicel, and the flagellum. The first two regions are single segments, whereas the third region, the longest one, is composed of eight flagellomeres. The scape and pedicel have microtrichia, chaetic sensilla, and rounded perforations. The flagellum is covered by different microtrichia, the morphology of which is described in detail. Two types of sensory pit are found on flagellomeres 1 to 6. An oval depression with trichoid sensilla extends from flagellomeres 4 to 6. On both sides of flagellomere 8 is a lanceolate depression covered by hair-like microtrichia. Morphometric and morphological analyses revealed some sex-related differences. The results of the SEM investigations are compared with those obtained on other species of the family Stratiomyidae and other brachyceran Diptera. The possible role of sensilla in sensory perception is also discussed in comparison with nondipteran species.
A scanning electron microscopy investigation of the antenna and maxillary palp of the adult of Sarcophaga tibialis Macquart (Diptera: Sarcophagidae), a species of medical, veterinary, and forensic relevance, is presented for the first time. Adults of both sexes used in this study were obtained from larvae collected in a case of traumatic myiasis in a domestic cat in northern Italy. The antenna of S. tibialis is that typical of cyclorrhaphan Diptera, consisting of three segments: the scape, the pedicel, and the postpedicel, bearing the arista. The scape is covered by microtrichia and has a row of long chaetic sensilla. The pedicel is also covered by microtrichia and has three types of chaetic sensilla and a cluster of setiferous plaques. Trichoid, styloconic, clavate, and basiconic sensilla are distributed among the microtrichia on the postpedicel. Invaginated basiconic-like sensilla and olfactory pits are also present, the latter ones more numerous in the female. Our results are compared with those obtained for other calyptrate flies, mainly in the family Sarcophagidae. The data obtained may represent a basis for electrophysiological studies on the sensorial activity of the species related to the search for food sources, mates, and suitable larviposition sites, and for comparative morphological studies with other Diptera.
The olfactory organ of an insect is formed by a pair of head appendages, the antennae which carry arrays of innervated hair structures, the sensilla. The antennae are the most important multimodal sensory organs for the insects and their relatives, bearing not only the sensilla of olfaction, but also those of taste, mechano-, hygro-, and thermoreception, and sometimes sensors for CO2. For many insects, the olfactory sense, and therefore the antenna, is of utmost importance not only in their search for food for themselves or their offspring, but for intraspecific communication as well, for example in ants or moths.
While antenna is the main organ for insect to accept the external chemical signals, the antennal sensilla that are diverse in structure and function form the insect receptors in chemical communication. Since a variety of Pseudacteon species are important natural enemies of the red imported fire ant, Solenopsis invicta Buren (. invicta), to elucidate the types of Pseudacteon sensilla will promote the study and understanding of the selection behavior ofPseudacteon in parasitizing. invicta. This study has used scanning electron microscope (SEM) to observe and investigate the females antennal sensilla of three Pseudacteon species, the Pseudacteon (P.) lit oralis, P. obtusus, and P. tricuspis, and demonstrated that there are four types of sensilla, the trichoid, basiconic, coeloconic, and chaetic sensilla, on their antennal flagellum. Among them, the former three are common in all three species, with trichoid sensillum as mostly abundant, while the chaetic sensillum exists only in the antennae of P. obtusus. The trichoid sensilla exhibit significant interspecies variations and are further classified into two subtypes based on the presence or absence of protrusions, the surface of which contains different shades of groove-like or irregular punctate structures. The basiconic sensilla resemble short spines with densely porous structures on the surface and are in the length of 7.3-9.8 μm and the width of 1.3-1.6 μm, upright or slightly bent. The coeloconic sensilla are irregularly formed in the middle and base of the flagellum, without surface pores; each coeloconic sensillum has eight finger-like folds in unequal lengths, while the end of the fold resembles a blunt cone. The chaetic sensilla enlarge at the base, possess multiple fold-like structures and fine-tipped ends, and are approximately 5 μm in length.