Haemocytes of the hemlock woolly adelgid Adelges tsugae Annand (Hom., Adelgidae) and changes after exposure to low temperatures

The main cellular components of the haemolymph of Adelges tsugae Annand wer e identified from individuals collected in Massachusetts, USA in February a nd October 1997. The cell types present were formative cells, plasmatocytes , adipohaemocytes, vermiform cells, prohaemocytes and oenocytoids. Vermifor m cells were the most abundant. Very few oenocytoids were found. They were significantly more cells of all types in the haemolymph of A. tsugae collec ted in October than in those collected in February. Adelges tsugae collecte d in February were exposed in the laboratory to -20, -25 and -30 degrees C for 2, 4 and 8 h. No intact cells were found in the haemolymph of A. tsugae exposed to -30 degrees C. Haemocytes were damaged by exposure to -20 and - 25 degrees C. The effect of these temperatures on the different cell types is presented.