Characterization of genetic diversity of some serovars of Bacillus thuringiensis by RAPD.

RAPD based fingerprinting of 21 serovars of Bacillus thuringiensis (Bt) representing different serotypes was performed using 19 random decamer primers. A total of 172 polymorphic fragments, ranging in size from 161-2789 bp, were amplified from 13 of the 19 primers. Pairwise genetic similarity analysis revealed very low similarity values, ranging from 3-68%, among the serovars of Bt, indicating high genetic divergence. Nineteen serovars of Bt fell in two major clusters and remaining two formed solitary clusters in the dendogram. Clustering of Bt strains established genetic relatedness between serovars and serotypes. It has been suggested that RAPD analysis can be used for genotypic characterization of Bt to complement flagellar serotyping.

Respiratory responses and blood sugar level of the crab, Barytelphusa cunicularis (Westwood), exposed to mercury, copper and zinc.

Barytelphusa cunicularis (Westwood), a freshwater crab was exposed to mercuric chloride, copper sulphate and zinc sulphate from 0 to 12 hr and the oxygen consumption of the animal was measured in order to study the stress caused by these heavy metals. Normal oxygen consumption was affected by the three heavy metals. Similarly, crabs exposed to sublethal concentrations of the same pollutants for 24, 48, 72 and 96 hr showed an elevation in the blood sugar level with a maximum increase at 48 hr. The results indicate a switch towards glycolysis in order to overcome the anaerobic stress caused by the heavy metals.

Susceptibility studies on Culex tritaeniorhynchus Giles, 1901, to insecticides in the state of Goa.

Tests conducted on the adults of C. tritaeniorhynchus in Goa during 1988-89 against organochlorine, organophosphate and carbamate insecticides showed that the LC50 values against DDT and dieldrin after 1 h of exposure were 2.2 and 1.2 per cent respectively. The LT50 values against malathion (5%), fenitrothion (1%) and propoxur (0.1%) were 19, 22 and 35 min respectively. Thus, taking into consideration the base-line data available for C. quinquefasciatus, the species can be considered susceptible to dieldrin, malathion, fenitrothion and propoxur. However, the results with DDT were equivocal and require verification.

Isolation of Japanese encephalitis virus from Culex pseudovishnui Colless, 1957 (Diptera: Culicidae) in Goa.

A strain of Japanese encephalitis virus was isolated from a pool of 54 female C. pseudovishnui Colless, 1957. The mosquitoes were collected in August 1988 during the period of epidemic of JE. This is the first report of isolation of JE virus from mosquitoes in Goa in the western coastal belt of peninsular India. In view of this isolation, C. pseudovishnui acquires greater importance, even though its density and relative prevalence during the current study was found to be far lower than C. tritaeniorhynchus.