Dr. Murai Éva szerk.: Parasitologia Hungarica 20. (Budapest, 1987)

Scanning electron microscopy has opened new prospects for researchers to discover unknown morphological details (PAYSINGER et al., 1983; BROCE and ELZINGA, 1984; IWASA, 1984). The new SEM observations indeed, improved our knowledge of morphology, however the function of the mouthparts of the secretophagous flies and their harmful effect to the host animals were not much dealt with in those works. MAHANKO (1973) described the morphology of the prestomal teeth of 13 species of the genera Hydrotaea and Musca, and he classified those muscoid species in three categories of "parasitism" based on the size, measurements of the prestomal teeth and the life-habits of the given species (where e. g. the place of Musca do mestica was rather questionable. Below not only those parts of the proboscis are described which have the ability to cause harm to the epithelia (see e.g. MEDVECZKY et al., 1988) but evidence was also sought for the details of the effects of the mouthparts causing microlesions. Of course, several pictures are also included here which show hitherto known features and do not provide new findings but which promote understanding a morphological-functional treatment, or, which show simply the usefulness of the SEM studies in this field. MATERIALS AND METHODS The specimens of a WHO strain Musca domestica and those of Musca autumnalis were obtained alive from the insectarium of the Parasitological Department, University of Veterinary Science, Budapest; the specimens (dry museum specimens) of Musca osiris were obtained from the collection of the Zoological Department, Hungarian Natural History Museum, Budapest. Carbon tetrachloride (CCI4) was used for killing the flies and assuring the reproduction of the physiological positions of the labella (for details see KOVÁCS-SZ. and GONDÁR, 1986). After a few minutes of air-drying - which removes CCI4 residues - a cleaning procedure was applied by a bio-active washing powder. Then the heads of flies were cut off and after transversally halving and air-drying they were mounted on SEM stubs. Specimens were vacuumcoated with a thin layer of coal and gold prior to examining them on a Jeol JSM-35 scanning electron microscope. For examination of the living tissues with SEM - which served as tests showing the harmful effect of the mouthparts - the method of SULOCHANA and DERBYSHIRE (1977) was adopted with the alterations described in the paper of MEDVECZKY et al. (1988). For testing the harmful effect of the different parts of the proboscis, flies were immobilized on the same way as it has been previously described (MEDVECZKY et al., 1988). RESULTS Based on the hitherto known references, first of all as regards the functions of proboscis, our examinations were concentrated to the haustellum and to the labella (Fig. 1), considering also the aims of our trials with living flies. Prior to an actual functioning, the proboscis of the muscoid flies emerges from the subcranial cavity through the movement of the muscles inserted to the inner chitinous skeleton of the proboscis and through the extra amount of haemolympha which is pressed into the volumen of proboscis. The contraction of the proboscis is also a result of active contractures (WEST, 1951; GREENBERG, 1973). However, this stretchy organ contains rather numerous stiffening elements, particularly so for the haustellum. For causing microlesions, the labrum and the hypopharynx seem the most dangerous elements at first glance, since both these structures are borne on a firm base on the rostrum, both are well-sclerotized and extremely sharp (WEST, 1951); the tips of both these structures terminate between the lamellae of the labella. The labrum, which covers the dorsal surface of the proboscis, is comparatively easy to examine (Fig. 2). Contrarily, the other "dagger", namely the hypopharynx which forms the ventral wall of the food-channel in the haustellum, is hardly accessible and in addition, is easily breakable while preparing off the plates of the mentum (Figs 3-6). The complex of the labrum and the hypopharynx form the food-channel, and they are extremely stiff when forming that tube. Our Fig. 7 shows clearly the position of the labrum-hypopharynx inside the haustellum, where we managed to bend the