Morphological and biochemical characteristics of two forms of Hybomitra typhus (Diptera: Tabanidae).

The tabanid Hybomitra typhus (Whitney) is widely distributed throughout the northern zones of all Canadian provinces and territories, in the north-western United States, Alaska, Minnesota and Michigan and in the east along the Appalachian highlands to South Carolina. It is known to attack man and livestock, and the larvae have been found in saturated moss from bogs, swamps and lake shores. It is variable in colour. Two morphologically distinct forms recorded in 1961 flying together at a large Sphagnum bog near Ottawa are referred to as forms A and B. They were again taken flying together in a large bog in Prescott, Ontario, in July 1974. Morphological characters used to distinguish the forms, which have been clearly segregated by size and colour characters, are described in this paper, and an electrophoretic examination of enzyme variants at the esterase loci, which provides additional diagnostic characters, is recorded. The combined data indicate that flies recorded as H. typhus comprise more than one species. The common form B predominated in mid-July 1974, whereas the variant form A occurred in much greater numbers in collections in late June 1975.