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

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.

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

“…magnifica ) enclose the postpedicel, have been reported in many bot fly species in different families [ 38 ]. The significantly enlarged pedicel are reported in obligate parasitic flies, such as the mouse warble fly genus Portschinskia [ 34 ] and the louse fly [ 45 , 46 ], and thus are common characteristics of the subfamilies Gasterophilinae, Oestrinae, and Hypodermatinae ( Table 2 ). These structures were speculated to protect the numerous fragile sensilla on the postpedicel surface from mechanical damage [ 46 , 47 ], but they may also obstruct the olfactory functions of antennae by reducing the chances for the sensilla to interact with odour molecules in the air.…”

“…The significantly enlarged pedicel are reported in obligate parasitic flies, such as the mouse warble fly genus Portschinskia [ 34 ] and the louse fly [ 45 , 46 ], and thus are common characteristics of the subfamilies Gasterophilinae, Oestrinae, and Hypodermatinae ( Table 2 ). These structures were speculated to protect the numerous fragile sensilla on the postpedicel surface from mechanical damage [ 46 , 47 ], but they may also obstruct the olfactory functions of antennae by reducing the chances for the sensilla to interact with odour molecules in the air. The exact function of these paradoxical structures remains to be determined, perhaps by using techniques that can manifest the details of the interaction between airflow and the insects [ 48 ].…”

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

“…Despite the availability of the keys for detailed identification of the anatomical structures of H. equina , a comprehensive analysis of micro-details requires specialized equipment, such as a scanning electron microscope. Some recent articles presenting high-resolution photographs verify and provide details of these anatomical structures [ 8 , 9 , 10 , 11 , 12 ].…”

“…Moreover, the latest research [ 12 ] has indicated that the host seeking process in H. equina involves various stimuli perceived mainly by specific sensory structures on the antennae, which are the essential olfactory organs. The researchers made a particularly interesting discovery that will be briefly discussed below.…”

“…Based on the analysis of the specific structure of antennas in H. equina , Andeani and co-authors [ 12 ] have proposed an interesting hypothesis. They have suggested that the localization of the hosts at medium and long distances by winged adult hippoboscids is mainly facilitated by sensilla; nevertheless, this complex process involves visual stimuli as well.…”