March, 1957]
P.
BALARAMA
MENON
15
the large numbers of egg masses collected from different Divisions of Rajasthan,
it was observed that some of the batches of tabanid eggs obtained from Jal Mahal
tank in Jaipur were parasitised and when they were kept in a moist chamber, large
numbers of small hymenopterous insects were found emerging from them. These
parasites appeared quite different from the species of Telenomus reported from
Uttar Pradesh. The insects which emerged from the eggs collected from Jaipur
were sent for identification and confirmation to the Commonwealth Institute of
Entomology, London, and have been identified as belonging to an indeterminate
species of Centrodora of the family Encyrtidæ (Hymenoptera). This appears to
be the first record of this species parasitising eggs of tabanid flies in India. It was
not possible to determine what species of Tabanidæ the parasitised eggs belonged
to, but it was probable that they may be of Atylotus which were found laying eggs
on grass in Jal Mahal tank in Jaipur from where the infected egg masses were
collected. Many adults of Atylotus were collected while in the act of oviposition
from the same site and no other species was in evidence at that time. The possibility
of utilising these parasites in the biological control of tabanid flies is yet to be
investigated.
SUMMARY
This report presents for the first time, data regarding the occurrence of surra
and tabanid flies in Rajasthan and Ajmer. Though the area is generally dry, surra
is prevalent in camels in Rajasthan. There is an increase in the incidence of surra
in the post-monsoon months reaching the climax in October and November when
the fly breeding is also expected to be at its highest. The incidence continues
during the early part of winter and gradually declines towards summer and is the
lowest during April and May when the water sources are dried up and fly breeding
is completely stopped.
The disease is more common in the moist regions, viz. eastern half of Rajasthan
including eastern half of Jodhpur Division. Udaipur and Kota are the two Divi-
sions affected most. Pali has the highest incidence of surra recorded so far. Since
camels of the arid region of Jodhpur and Bikaner Divisions come in contact with
the diseased ones, when taken for foraging, they get the infection during the fly
season. Hence cases of surra are not uncommon in Jodhpur and Bikaner Divisions
also. Surra cases are also reported from Ajmer but the majority of them are
believed to be from camels brought from outside the State.
A tabanid survey was conducted in the area with special emphasis on the
breeding places and it was established that the transmission of surra took place in
the area through the agency of the flies which were present, in all the Divisions of
Rajasthan and Ajmer and which could breed and complete their life cycle under
conditions prevailing there. Even " waterless " Bikaner with an average annual
rainfall of 7. to 8 inches was not free of them. Large numbers of the different stages
of these flies, viz. egg, larva, pupa and adult, were collected from different Divisions
and four species of Tabanidæ, viz. Tabanus rubidus, T. striatus, T. macer and an
undetermined species of Atylotus have been recorded. These are new records for
the locality.