376
Bionomics of the Ox Warble-Fly
born and bred at Mukteswar, whilst towards the end of April 1937, the writer
actually observed what appeared to be an adult H. lineatum in a locality
adjoining Naini Tal (altitude 5,000 ft.) but which unfortunately he was unable
to secure. Additional evidence in support of this statement is provided by
the fact that the oesophageal forms of H. lineatum larvae have been recovered,
during July 1937, from bulls maintained at Mukteswar since October 1936.
In January 1937, a systematic survey was undertaken with a view to
obtaining an indication as to the extent of warble-fly infestation in hill bulls
at Mukteswar, including those housed in the out-kraals of the station. In all,
372 bulls were examined, out of which 198 (53.23 per cent) showed warble
tumours in their backs, the maximum number of warble tumours observed in a
single animal being fifty-three. Nearly fifty-five mature larvae were pressed
out from some of these tumours and all of these were identified as Hypoderma
lineatum, which so far has been the only species of Hypoderma recorded in
this locality.
From the foregoing figures, it would appear that H. lineatum is well estab-
lished in the Kumaun hills, and it would be of interest to enquire into the
possible factors that determine the occurrence of this pest at such high altitudes.
It is worthy of note that similar observations have also been recorded in the
United States of America by Bishopp and his collaborators [1926], for, according
to these authors, warble-flies seem to thrive well in fairly high altitudes, this
being specially true with Hypoderma lineatum, which is known to be abundant
at elevations above 7,000 ft. The evidence so far available would seem to
suggest that the pest is not influenced—at any rate, to any appreciable extent—
by conditions of temperature and topography, as is evidenced by the fact that
H. lineatum is also abundant in the Punjab which, in respect of both these
ecological factors, is very different from the Kumaun hills. The difference in
temperature conditions between the two localities may, however, provide an
explanation for the fact that while at Mukteswar it was observed that the
warble tumours continued to appear in the backs of cattle till early March, at
Hissar (Punjab), no tumours were reported to have been observed after the
middle of January. It is of interest to note that in the course of a short tour
which the author undertook in the Punjab during the winter of 1937, the pest
was most prevalent in areas where rainfall was scanty and the soil was sandy
loam. The districts of Hissar and Ferozepore were found to be comparatively
heavily infested, while, as already recorded by Cross [1926], goat warbles were
most common in the " Barbary " breed in the Salt Range area in the
Jhelum district.
III. THE OESOPHAGEAL FORMS
It is of interest to observe that the oesophageal forms of H. lineatum
larvae have been found to occur at Mukteswar, continuously from the end of
March 1937 to the date of writing (October 1937). This is a point which it
would seem difficult to reconcile with the generally accepted view that H.
lineatum has only one brood in a year. The occurrence of these forms has also