Pathogenesity of thai sacbrood virus to the ecotypes of Apis cerana indica Fab. in Kerala
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Date
1998
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Department of Agricultural Entomology, College of Agriculture, Vellayani
Abstract
Identification of ecotypes of the Indian bee A. cerana indica Fab.
in different ecological niche in Kerala adopting statistical analysis of
the morphometric data was attempted in the investigation. Sixty worker
bees each were collected from 18 locations distributed throughout Kerala
and data on 50 selected characters were collected. Univariate analysis
showed significant variations in the data with reference to all the fifty
characters indicating the desirability of a multivariate analysis for
identifying sub groups of A. cerana indica available in the state.
A comparison of the honeybee population of the three topographic
divisions of the state viz., highrange, highland and midland, with reference
to each morphometric character revealed that the bees from highrange
were distinct from those of highland and midland. There was less
distinction between the bees of the latter two divisions. It also indicated
that the highrange bees possessed longer proboscis, antennae, wings and
legs. The abdominal size also showed an increasing trend in highland and
highrange bees.
Eleven morphometric characters were positively correlated with
altitude while seven characters showed negative correlation.
Multivariate(discriminant) analysis of the morphometric data
revealed the existence of four different clusters / ecotypes in A. cerana indica
populations of Kerala. Cluster I included all the six locations of midland
and four locations of highland. Two locations of highland at higher altitude
formed cluster 11. Pampadumpara of the highest altitude in highrange came
in cluster IV and remaining locations of the highrange constituted cluster
Ill.
Contribution of each morphometric character towards divergence
of the clusters was also assessed. Seventeen characters contributing 2.5
to 6.4 per cent of divergence were thus identified.
Bees from all the four clusters / ecotypes showed susceptibility to
Thai Sacbrood Virus (TSBV) infection.
Studies on the pathogenicity of TSBV showed that all four larval
instars of A. cerana indica were susceptible to TSBV. One day old larvae
were highly susceptible recording 100 per cent mortality closely followed
by 2 and 3 day old larvae showing 84 to 92 and 82 to 96 per cent mortality
respectively, with an incubation period of 3-4 days. Four day old larvae
were comparatively less susceptible recording 72 to 74 per cent mortality
with an incubation period of 3 to 5 days.
The infected larvae were seen lying on the floor of the brood cells
on their back with the head directed outwards and turned upwards like the
prow of a boat. In later stages they became plumbier than healthy larvae.
After death each larva showed a sac like appearance when lifted up and it
was filled with a milky fluid formed probably by the histolysis of the tissues.
In 10 to 15 days the sac got shrunk into a small browinish black scale
\ "
loosely lying at the floor of the' cell. The presence of diseased larvae was
found to upset the behaviour of workers and queen. These resulted in the
fast dwindling of the population and cessation of cleaning activities in the
hive. The hive lost the desired qualities of a bee abode and hence the
surviving bees deserted the same causing total loss to apiary.
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