Ultrastructural investigation of antennae in three cutaneous myiasis flies: Melophagus ovinus, Hippobosca equina, and Hippobosca longipennis (Diptera: Hippoboscidae)

Hippobosca equina L. (Hippoboscidae: Hippobosca)-An Old Enemy as an Emerging Threat in the Palearctic Zone

Arthropods of the Hippoboscoidea superfamily are parasites of animals from various systematic groups. Mass appearances of these insects and their attacks on people are increasingly being recorded. Their parasitism has a negative effect on host well-being, as it causes feelings of agitation and irritation as well as skin itching and damage. It may result in weight loss and development of diseases in the long-term perspective. Parasites can be a potential epidemiological threat for their hosts as well. One of such parasites is a cosmopolitan species of the Hippoboscinae subfamily-Hippobosca equina. Studies have confirmed the presence of Corynebacterium pseudotuberculosis equi, Bartonella spp., and Anaplasma spp. in the organism of these insects. The frequency of anaphylactic reactions caused by H. equina attacks has been increasing. The aim of the present paper was to summarize the up-to-date knowledge of Hippobosca equina Linnaeus, 1758 due to its significance in medical and veterinary sciences as a potential vector of pathogens. Given the increasing expansion of ectoparasites, mainly related to climate change, ensuring animal welfare and human health is a priority.

Finding a suitable coat: The ecology of the invasive deer ked (Lipoptena cervi (Linnaeus, 1758); Diptera: Hippoboscidae), an ectoparasite of large mammals in the Czech Republic

Some parasitic diseases of wild animals are transmissible to humans and cause health problems. A widespread ectoparasite of vertebrates is the deer ked, Lipoptena cervi ((L.); Diptera: Hippoboscidae). We studied the interaction of this parasite with habitat-related, host-related, and temporal factors in the Czech Republic. We analysed observations of its abundance in hunted wild animals in the context of their environment. Our results confirmed that cervids are a preferred host species. Most of the other relationships between ked abundance and the studied factors were probably due to the olfactory preferences of keds. Males and older individuals of the game host species were more attractive to the parasites for this reason. The higher abundance of keds at the beginning of the hunting season can be explained by their phenology. The deer ked can significantly affect the management of game species. We conclude that its preference for older male cervids is important for the future conditions of game animals. The population densities of deer keds in areas with high parasitization rates could thus be influenced by active game management.

Comparative morphology of antennal ultrastructure in Tachinidae parasitoid flies (Diptera): The phylogenetic importance of antennal sensilla

Tachinidae are one of the most diverse clades of Diptera. All tachinids are parasitoids of insects and other arthropods, and thus are considered an important source of biological pest control. Antennae are the most important olfactory organs of Tachinidae playing key roles in their lives, especially in locating hosts, and details of antennal ultrastructure could provide useful features for phylogenetic studies and understanding their adaptive evolution. Despite the ecological and evolutionary importance of antennae, the current knowledge of antennal ultrastructure is scarce for Tachinidae. Our study examined antennal sensilla of thirteen species belonging to thirteen genera within eleven tribes of all the four subfamilies (Phasiinae, Dexiinae, Tachininae, and Exoristinae): Beskia aelops Walker, Trichodura sp., Voria ruralis (Fallén), Zelia sp., Cylindromyia carinata Townsend, Phasia xenos Townsend, Neomintho sp., Genea australis (Townsend), Copecrypta sp., Hystricia sp., Belvosia sp., Leschenaultia sp., and Winthemia pinguis (Fabricius). Types, length and distribution of antennal sensilla were investigated via scanning electron microscopy (SEM). Our comparative analysis summarized 29 variable characters and we evaluated their phylogenetic signal for subfamilial, tribal and generic/specific levels, showing that antennal ultrastructure could be a reliable source of characters for phylogenetic analysis. Our findings demonstrate the remarkable diversity of the antennal ultrastructure of Tachinidae.

Insights into the Antennal Characteristics and Olfactory Strategy of the Endangered Rhino Stomach Bot Fly Gyrostigma rhinocerontis (Diptera: Oestridae)

Gyrostigma rhinocerontis (Diptera: Oestridae) is a rare obligate intestinal parasite of both white and black rhinoceroses, which can induce severe myiasis, cause secondary infection, and lead to enormous economic and scientific loss. Antennae are the main sensory organs of G. rhinocerontis, which may have evolved a series of specialized adaptive structures to facilitate the exploitation of their hosts. Here, we thoroughly examine the antennae of G. rhinocerontis via light and scanning electron microscopy. Only microtrichia and chaetic sensilla were observed on the scape and pedicel, and the latter is enlarged, half-enveloping the postpedicel. Four types of sensilla (trichoid sensilla, basiconic sensilla, coeloconic sensilla, and clavate sensilla) and sensory pits are detected on the postpedicel. A set of coeloconic sensilla and a chaetic sensillum are located on the arista. Distribution, type, size, and ultrastructure of antennal sensilla are presented. The antennae of G. rhinocerontis are the largest among Oestridae species, with the most sensilla and the most sensory pits. These antennal characteristics could be correlated to their adaptation for more sensitive and accurate olfactory organs, used to locate their rare and endangered hosts. Accordingly, this morphological evidence supports that the host is an important driving factor in the diversity of antennal morphology in the bot flies.

Ultrastructure of Antennal Sensory Organs in Nine Flesh Flies (Diptera: Sarcophagidae): New Insight into the Definition of Family Sarcophagidae

Simple Summary

The antennal sensilla of species in all three subfamilies of Sarcophagidae are studied for the first time via scanning electron microscopy. The morphology, density, and distribution of each type are described for each species. A total of eight types of antennal sensilla (chaetic sensilla, setiferous plaques, pedicellar buttons, trichoid sensilla, basiconic sensilla, coeloconic sensilla, clavate sensilla, bottle-shaped sensilla) and sensory pits are found in both sexes. The existence of bottle-shaped sensilla in the sensory pits in all three subfamilies of the sarcophagid species suggests a potential synapomorphy of sarcophagids and a new morphological diagnosis character of the family Sarcophagidae.

Abstract

The antennae are the main olfactory organ of flies, playing key roles in their survival and the success of all life stages. Antennal ultrastructural morphology has been well described in the representative species of most calyptrate families, yet only a few studies have focused on Sarcophagidae species, those with ecological and medical relevance. Antennal morphology and the types, shapes, distribution, and density of the antennal sensilla of nine Sarcophagidae species are studied in detail with scanning electron microscopy, including Miltogramminae: Metopia campestris (Fallén) and Mesomelena mesomelaena (Loew), Paramacronychiinae: Agria mihalyii (Rohdendorf & Verves), Wohlfahrtia bella (Macquart), and W. magnifica (Schiner); Sarcophaginae: Sarcophaga (Parasarcophaga) albiceps Meigen, S. (Bercaea) africa (Wiedemann), S. (Boettcherisca) peregrina (Robineau-Desvoidy), and S. (Liosarcophaga) portschinskyi (Rohdendorf), covering all three subfamilies of this family. The morphology of the three segments of the antennae has been described. The scape has only one type of chaetic sensilla, while three subtypes of chaetic sensilla were detected on the pedicel. The postpedicel has four types of sensilla: trichoid sensilla, coeloconic sensilla, clavate sensilla, and three subtypes of basiconic sensilla. Bottle-shaped sensilla were observed in sensory pits on the postpedicel in all nine species. These sensilla have not been discovered in other calyptrate species, suggesting that they are a potential sarcophagid synapomorphy.

Antennal Morphology and Fine Structure of Flagellar Sensilla in Hippoboscid Flies with Special Reference to Lipoptena fortisetosa (Diptera: Hippoboscidae)

Simple Summary

In insects, host searching usually involves different kinds of stimuli, both visual and chemical, that may act in combination. External cues are perceived through specific sensory organs (sensilla), mainly present on the antennae. Understanding how ectoparasites belonging to the Hippoboscidae locate their hosts is crucial, since these flies infest animals and can attack humans, with veterinary and medical implications. The aim of this research was to study the antennae of four hippoboscid species, Lipoptena cervi (Linnaeus, 1758), Lipoptena fortisetosa Maa, 1965, Hippobosca equina Linnaeus, 1758, and Pseudolynchia canariensis (Macquart, 1840), investigating the morphology and the sensory structures present on these appendages. A typical conformation of the antennae with the envelopment of the third segment (flagellum) inside the first two have been observed. Moreover, two types of sensilla have been detected and their role in the perception of host odours and CO₂ have been hypothesized. Other antennal structures seem to be involved in the detection of temperature and humidity variations. Our findings confirm that these hippoboscids use chemoreception for host location, giving insights into this complex process in this poorly investigated group.

Abstract

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.

Evolutionary adaptations in four hippoboscid fly species belonging to three different subfamilies

Lipoptena cervi (Linnaeus, 1758), Lipoptena fortisetosa Maa, 1965, Hippobosca equina Linnaeus, 1758, and Pseudolynchia canariensis (Macquart, 1840) (Diptera: Hippoboscidae) are haematophagous ectoparasites that infest different mammal and bird species and occasionally attack humans. They are known for the health implications they have as vectors of pathogens to humans and animals, and for the injuries they inflict on their host's skin. This study focused on the morphological structures evolved by parasites in terms of their biology and the different environment types that they inhabit. To this aim, we examined four hippoboscid species, as well as their hosts' fur (ungulate and horse), and feather (pigeon) through light and Scanning Electron Microscopy (SEM) observations in order to highlight the main morphological features that evolved differently in these flies and to explain the effect of hosts' fur/feather microhabitats on the morphological specializations observed in the investigated ectoparasites. The studied species showed main convergent characters in mouthparts while remarkable differences have been detected on the antennal sensillar pattern as well as on the leg acropod that displayed divergent characters evolved in relation to the host.

Molecular evidence of bacteria in Melophagus ovinus sheep keds and Hippobosca equina forest flies collected from sheep and horses in northeastern Algeria

The sheep ked, Melophagus ovinus, and the forest fly, Hippobosca equina, are parasitic dipteran insects of veterinary importance. As hematophagous insects, they might be considered as potential vectors of diseases which may be transmissible to humans and animals. The purpose of this study was to present initial primary data about these two species in Algeria. To do so, we conducted a molecular survey to detect the presence of bacterial DNA in flies collected in Algeria. A total of 712 flies including, 683 Melophagus ovinus and 29 Hippobosca equina were collected from two regions in northeastern Algeria. Monitoring the monthly kinetics of M. ovinus infestations showed something resembling annual activity, with a high prevalence in January (21.67%) and May (20.94%). Real-time quantitative PCR assays showed that for 311 tested flies, 126 were positive for the Bartonella spp. rRNA intergenic spacer gene and 77 were positive for Anaplasmataceae. A random selection of positive samples was submitted for sequencing. The DNA of Bartonella chomelii and Bartonella melophagi were amplified in, respectively, five and four H. equina. 25 M. ovinus positive samples were infected by Bartonella melophagi. Amplification and sequencing of the Anaplasma spp. 23S rRNA gene revealed that both species were infected by Wolbachia sp. which had previously been detected in Cimex lectularius bed bugs. Overall, this study expanded knowledge about bacteria present in parasitic flies of domestic animals in Algeria.

Comparative morphology of the deer ked Lipoptena fortisetosa first recorded from Italy

Hippoboscidae flies parasitize various animal species. Knowledge about these insects remains sparse, although they are known to cause stress and damage to their hosts, and can also accidentally infest humans, causing different sanitary risks. Research conducted in Tuscany assessing the biology and distribution of Lipoptena cervi (Linnaeus, 1758) (Diptera: Hippoboscidae), the most common ectoparasite of ungulates in Italy, revealed the presence of Lipoptena fortisetosa Maa, 1965 in Italy for the first time. This study includes a morphological comparative description of L. cervi and L. fortisetosa, emphasizing the peculiar differences between the two species to facilitate their accurate identification. The most pertinent morphological differences between the two species are highlighted, such as the external features of the antennae, distribution of bristles, and different features in the external genitalia. In both species, scanning electron microscopy of mouthparts revealed strong adaptive convergence in the feeding apparatus. Modified palps and a very thin proboscis are described in relation to feeding behaviour.

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

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.

The antenna of horse stomach bot flies: morphology and phylogenetic implications (Oestridae, Gasterophilinae: Gasterophilus Leach)

Antennae are among the most elaborate sensory organs in adult flies, and they provide rich information for phylogenic studies. The antennae of five out of eight species of Gasterophilus Leach (G. haemorrhoidalis (Linnaeus), G. intestinalis (De Geer), G. nasalis (Linnaeus), G. nigricornis (Loew) and G. pecorum (Fabricius)), were examined using scanning electron microscopy. The general morphology, including distribution, type, size, and ultrastructure of antennal sensilla were presented, and the definition of auriculate sensilla and sensory pits were updated and clarified. Eighteen antennal characters were selected to construct the first species-level phylogeny of this genus. The monophyly of Gasterophilus was supported by the presence of coeloconic sensilla III on the antennal arista. The species-level cladogram showed G. pecorum branching off at the base, and the remaining species forming the topology (G. intestinalis+ (G. haemorrhoidalis+ (G. nasalis+ G. nigricornis))). Our research shows the importance of the antennal ultrastructure as a reliable source for phylogenetic analysis.

Ultrastructural Morphology of the Antenna and Maxillary Palp of Sarcophaga tibialis (Diptera: Sarcophagidae)

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.

Comparative ultrastructure of pretarsi in five calyptrate species

Pretarsi are the most important structures that allow flies to walk on various smooth surfaces and act as contact sensory organs. The pretarsal ultrastructure, including adhesive pads, claws, unguitractors, and bristles, of five calyptrate species are presented and described in detail, including Calliphora calliphoroides (Rohdendorf, 1931), Lucilia sericata (Meigen, 1826), Sarcophaga portschinskyi (Rohdendorf, 1937), Muscina stabulans (Fallen, 1817) and Portschinskia magnifica Pleske, 1926. Two types of tenent setae (spoon-tipped and spatula-tipped) are present on the ventral side of pulvilli in all species. The density of tenent setae and the pulvilli area in forelegs, midlegs, and hindlegs of both sexes are different. Among the five species, Ca. calliphoroides has unusually large pulvilli to its body size. These results provide morphological details that help to understand the movement and attachment of flies.

Scanning electron microscopy of antennal sensory organs of the cattle grub, Hypoderma lineatum (Diptera: Oestridae)

Hypoderma lineatum (Villers, 1789) (Diptera: Oestridae) is a hypodermosis fly that has resulted in great economic losses worldwide. The antennae of cattle grub males and females were examined through stereoscopic microscopy and scanning electron microscopy to reveal the general morphology, combined with distribution, type, size, and ultrastructure of the antennal sensilla. All of the three antennal segments (antennal scape, pedicel, and funiculus) possess microtrichiae on their surface. Mechanoreceptors only exist on the antennal scape and pedicel. The antennal funiculus presents four types of antennal sensilla: trichoid, basiconic, coeloconic, and clavate sensilla. Three distinctive characters of H. lineatum are obvious: (1) the relatively slender, flexible, and equal-height mechanoreceptors; (2) the enlarged antennal pedicel, and numerous antennal sensory pits and pit sensilla on the antennal funiculus; and (3) all types of antennal sensilla clustered in sensory pits, respectively. Additionally, the enlarged antennal pedicel and abundant sensory pits and pit sensilla might facilitate odor detection, enhance olfactory sensitivity and accuracy, and also protect the fragile antennal sensilla from mechanical irritation or damage.

Ultrastructure of antennal sensory organs of horse nasal-myiasis fly, Rhinoestrus purpureus (Diptera: Oestridae)

Rhinoestrus purpureus (Brauer, 1858) (Diptera: Oestridae) is an economically important parasite that can cause severe nasal myiasis in equids or even attacking humans. The antennae of R. purpureus were examined using stereoscopic microscopy and scanning electron microscopy. The general morphology was provided detailedly, together with distribution, type, size, and ultrastructure of antennal sensilla. All the three antennal segments, antennal scape, pedicel, and funiculus, are interspersed by microtrichiae. Only mechanoreceptors are detected on antennal scape and pedicel. On antennal funiculus, three types of sensilla were observed, including basiconic sensilla, coeloconic sensilla and clavate sensilla. Two features are characterized of this host-specific bot fly: (1) numerous sensory pits with branched basiconic sensilla on antennal funiculus and (2) the absence of trichoid sensilla. The function of these distinctive traits are discussed in association with the life history. We suggest that more sensory pits with branched sensilla could increase the sensitivity of olfactory system for host orientation, while the capability of pheromone identification might be reduced due to the absence of trichoid sensilla. Besides, we support both thermo- and chemo-functions of coeloconic sensilla.