ISOLATION AND CHARACTERIZATION OF ENTOMOPATHOGENIC ...

The fungal spray at higher dosage (1.2 x 10 12 ) after 7 days of second and third spray
only showed more than 50 per cent of mortality. The concentrations 2 x 10 12 and 2 x 10 10
performed at par with each other and significantly superior to all doses of V. lecanii at 7 DAS
and this trend continued at 14 DAS after the first and third spray.
Even at the lowest dose V. lecanii was significantly superior to untreated only at 7
and 14 DAS. After first spray there was no significant difference between all the doses of V.
lecanii and untreated control at 3 DAS, but inferior to chemical spray became evident (Table
45). However observations showed no difference between highest dose of V. lecanii (2 x 10 12 )
and succeeding dose (2 x 10 10 ). Conversely, the lowest dose (2 x 10 5 ) failed as badly as
untreated check throughout the study period at third day after each spray (Table 45).
Dimethoate, efficiently knocked down at the third day of first spray and continued to
maintain its effectiveness throughout the observation period.
4.12 CHEMICAL MUTATION
UV radiation
The conidial suspension of Ma2 and Vl1 exposed to UV radiation at 5 cms from UV
bulb resulted in an optimum killing percentage of 99.97 per cent. From the stock of
mutagenized survivors, totally twelve mutants from Vl1 and twelve mutants from Ma2 strain
were developed.
The test insects (H. armigera and B. brassicae) exhibited mortality to all mutants.
However, the mortality of V. lecanii mutants values ranged from minimum of 32.59 to
maximum of 91.97 per cent during the study (Table 46). Among Vl1 derived mutants highest
cumulative mortality of 91.97 per cent was observed on VA2, but failed to differ statistically
from other mutants, VA5 (90.56%), VA11 (91.96%) and VA12 (89.36%). The lowest mortality
was recorded with VA9 with only 32.59 per cent.
The M2 derived mutants exhibited moderate pathogenicity of H. armigera. The
mortality ranged from 36.50 in MH12 to 91.67 in MH4 and was on par with MH2 (90.92%).
The next best mutant was MH8 (82.75%) followed by MH5 (77.10%) and held type V1
(73.96%).