Insecticide bioassays were carried out on larvae and adults of rosy eye mutant and wildtype strains of A. aegypti. Both the strains were equally susceptible to DDT, malathion and deltamethrin. Biochemical assays showed an increase in acetylcholinesterase enzyme (AChE) activity in all the stages of mutant strain with both the substrates i.e. acetylthiocholine iodide and S-butyrylthiocholine iodide. However, there was no difference in the percent inhibition of enzyme activity with propoxur in these two strains. Polyacrylamide gel electrophoresis performed in native conditions on the homogenates of adults of rosy eye mosquitoes showed that AChE-II allele was highly active with the substrate acetylthiocholine iodide as compared to wildtype strain. Frequency of the highly active AChE-II allele in the mutant strain was about 68%, whereas it was about 5% in the wildtype strain.
Title: Post-inoculation changes in enzyme activity of Aedes aegypti infected with Chikungunya virus Mourya DT, Hemingway J, Leake CJ Ref: Acta Virologica, 39:31, 1995 : PubMed
Levels of acetylcholinesterase, non-specific esterases, glutathione-S-transferase and glucose-6-phosphate dehydrogenase in Aedes aegypti (L.) mosquitoes inoculated intrathoracally with Chikungunya virus were elevated, as compared to uninoculated control insects. A number of these enzymes are important in the insects defence mechanism against xenobiotics, such as pesticides. Malathion bioassays indicated a reduction in the susceptibility of experimentally injected insects with virus or virus-free inoculum, compared to non-inoculated controls. However, insects which were mock-inoculated (injected with no inoculum) showed a similar reduction in susceptibility suggesting that the observed effect was due to the mobilization of a defence reaction in the mosquitoes in response to injury during inoculation.
Title: Effect of sublethal dosages of insecticides on chikungunya virus susceptible and refractory strains of Aedes aegypti Mourya DT, Gokhale MD, Banerjee K Ref: Southeast Asian Journal of Tropical Medicine & Public Health, 25:536, 1994 : PubMed
Three strains of Aedes aegypti mosquitos viz (i) CRS, refractory to Chikungunya (CHIK) virus by oral route of infection but susceptible to DDT (2) CSS, susceptible to CHIK virus and also susceptible to DDT (3) CSS-DDTR, susceptible to CHIK virus but resistant to DDT, were examined for the effect of sublethal dosages of DDT and deltamethrin on their fecundity. Biochemical analysis showed that there was an increase in glutathione s-transferase activity in the CSS-DDTR strain which was associated with DDT resistance. There was an increase in acetylcholinesterase activity in the CRS strain, however it was not associated with resistance to all the three insecticides tested. No significant differences in the fecundity of these three strains were observed, though there was some increase in the number of non layers in CSS-DDTR strain after the treatment of DDT and mean number of eggs laid by CSS and CRS strains was slightly reduced (0.5 > p < 0.1) after the treatment with deltamethrin.
Title: Insecticide susceptibility status & enzyme profile of Aedes albopictus populations from different localities of Maharashtra state Chakraborti S, Mourya DT, Gokhale MD, Banerjee K Ref: Indian J Med Res, 97:37, 1993 : PubMed
Susceptibility status of five populations of Ae. albopictus mosquitoes from Maharashtra state, to DDT, malathion, fenitrothion, bromophos, propoxur and deltamethrin was studied and compared with the laboratory population. Four populations survived when adults were exposed to 4 per cent DDT impregnated paper for 2 h; though three of these populations had lower DDT-LC50 values at larval stages in comparison with the laboratory population. Results of topical application of DDT on these four populations supported these findings by showing comparatively higher LD50 values at adult stages in comparison with the laboratory population. All the populations were highly susceptible to other pesticides tested i.e., malathion, fenitrothion, bromophos, propoxur and deltamethrin. These populations were distinguished from each other by esterase isoenzyme patterns.
Title: Changes in enzyme titres with age in four geographical strains of Aedes aegypti and their association with insecticide resistance Mourya DT, Hemingway J, Leake CJ Ref: Medical & Veterinary Entomology, 7:11, 1993 : PubMed
The enzymes acetylcholinesterase, glutathione S-transferase (GST), glucose 6-phosphate dehydrogenase (G6PD), and general esterases were assayed in four strains of Aedes aegypti mosquitoes aged between 1 and 30 days. Microtitre plate methods were used to assay activity in the homogenates of individual mosquitoes. The levels of GST and G6PD declined with the age of the mosquitoes, while the activity for the other enzymes remained constant. Soluble protein content was also found to decline with mosquito age in all the strains. Insecticide bioassays showed that two strains (Trinidad and Virtudes) of Ae. aegypti were resistant to DDT, deltamethrin and malathion, whereas two other strains (Bangkok and Indian) were susceptible to all four classes of insecticides tested. Higher esterase activity levels in the resistant compared to the susceptible strains were assumed to be the cause of organophosphate resistance. The combination of DDT and deltamethrin resistance in two strains with normal GST and G6PD characteristics suggests that a kdr-type nerve insensitivity mechanism may be involved.
