MORPHOLOGICAL DIFFERENCES IN PROTHORACIC SPIRACLES BETWEEN THREE STRAINS OF APIS MELLIFERA (L). EXISTENCE OF A RESISTANCE MECHANISM AGAINST ACARAPIS WOODI G. Theophilidis, F. HATJINA 1 , A. Gregorc, N. Pappas, St. Zacharioudakis, A. Thrasyvoulou 1 Hellenic Institute of Apiculture, N. Moudania 63 200, Greece E-mail:apicinst@instmelissocomias.gr INTRODUCTION A morphomentric study was contacted on the prothoracic spiracles of Apis mellifera macedonica, Apis mellifera ligustica and Apis mellifera carnica. Apis mellifera macedonica is a sub-species of Northern Greece, which shows resistance to Acarapis woodi. In Southern Greece, since Apis mellifera ligustica has been introduced, tracheal mite infestations have become severe. Apis mellifera carnica, which is also susceptible to Acarapis woodi, was used in this study for comparative reasons. Keywords: Apis mellifera / morphometry / spiracles / Acarapis woodi / resistance METHODS AND MATERIALS The parts of the cuticle (2 x 1mm) with the left and right prothoracic spiracles (including the auricle, the lobe and part of the trachea, nomenclature from Snodgrass, 1956) were removed and cleaned from the cut ends of muscle fibres. The dissected parts of the cuticle (including part of the trachea) were then dehydrated in a graded series of ethanol (30%, 50% 70% and 100%) and were finally mounted on slides for light microscopy. The preparations were examined with a Leica DMLB microscope and photographed using the Image Pro Plus software (by Digital Image Systems). The facilities of the image analysis system permitted the accurate measurement of certain dimensions of the spiracles like the length of atrium (LA, see Fig. 1), the width of atrium (WA) and the area of the atrium (AA). RESULTS Figure 2 is an image of a prothoracic spiracle of A. mellifera. The statistical analysis on the measurements of the specific dimensions of the spiracle (as shown in Fig. 1) revealed significant differences between the bee strains examined: the length of atrium was found to be 800 ±91µm and 751 ± 52µm respectively for A. m. ligustica and A. m. carnica (larger by 21% and 14% respectively) compared with A. m. macedonica (658 ± 48µm) (Fig. 3). The width of atrium was found to be 230 ± 34µm and 197 ± 20µm respectively for A. m. ligustica and A. m. carnica (larger by 29% and 14% respectively) compared with A. m. macedonica (177 ± 21µm) (Fig. 3). The most important parameter, the area of atrium was also found to be significantly larger in A. m. ligustica (148,900 ± 17,100µm 2 ) and in A. m. carnica (132,100 ± 14,500µm 2 ) (by 46% and 29% respectively) compared with A. m. macedonica (101,800 ± 16,900µm 2 ) (Fig. 4). The cross-diameter at the opening of the trachea was found to be 221 ± 19µm in A. m. ligustica and therefore 8% larger than the trachea of A. m. macedonica (204 ± 22µm). About 600µm from the outer part, the cross-diameter becomes significantly larger for both strains and finally tapers significantly to 236µm and 197µm for A. m. ligustica and A. m. macedonica respectively. 62