Pyrethroid susceptibility & enzyme activity in two malaria vectors, Anopheles stephensi (Liston) &. A. culicifacies (Giles) from Mysore, India.
OBJECTIVE
Anopheles stephensi and A. culicifacies are the two major vectors of malaria in Karnataka. These mosquito populations are continuously being exposed directly or indirectly to different insecticides including the most effective pyrethroids. Therefore, there is a threat of insecticide resistance development. We subjected these vectors to larval bioassay using two popular pyrethroids viz deltamethrin and permethrin. An attempt was also made to correlate the activities of certain detoxifying enzymes such as A- esterase, B-esterase, glutathione-S transferase (GST) and glucose-6-phosphate dehydrogenase (G6PD) with the tolerance levels of the two vectors.


METHODS
Larval bioassay was carried out following the standard WHO procedure on field-collected larvae. The LC50 and LC90 values were calculated following Probit analysis. Biochemical estimations were done with a U V spectrophotometer and the isozyme studies employing native polyacrylamide gel electrophoresis (PAGE).


RESULTS
The results of the larval bioassay revealed that A. stephensi has more tolerance to deltamethrin than A. culicifacies and vice versa for permethrin. Biochemical estimations revealed significantly (P < 0.05) higher levels of A-esterase and GST activity in A. stephensi whereas A. culicifacies showed significantly higher (P < 0.05) levels of B-esterase and G6PD activity. The total larval protein assayed was found to be more (P < 0.05) in A. stephensi. The isozyme profiles also revealed difference in mobility, intensity and the number of bands.


CONCLUSIONS
As these malaria vectors are exposed to different kinds of insecticides, they develop increased enzyme activities to overcome the insecticide pressure. This has enhanced the tolerance level against the pyrethroids tested. Thus, A. stephensi was found to be tolerant to deltamethrin depicting a higher activity of A-esterase and GST enzymes, whereas the higher activity of B-esterase and G6PD has resulted in the development of tolerance to permethrin in A. culicifacies.
Ganesh
K N
KN
Department of Studies in Zoology, University of Mysore, Manasagangotri, Mysore, India.
Urmila
J
J
Vijayan
V A
VA
D000818:Animals; D000852:Anopheles / Q000187:drug effects / Q000201:enzymology* / Q000254:growth & development*; D001681:Biological Assay; D004361:Drug Tolerance; D004950:Esterases / Q000378:metabolism; D005954:Glucosephosphate Dehydrogenase / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D007306:Insecticides / Q000494:pharmacology*; D007814:Larva / Q000187:drug effects / Q000201:enzymology; D009570:Nitriles; D026023:Permethrin / Q000494:pharmacology*; D011722:Pyrethrins / Q000494:pharmacology*
D007306:Insecticides; D009570:Nitriles; D011722:Pyrethrins; C017180:decamethrin; D026023:Permethrin; D005954:Glucosephosphate Dehydrogenase; D005982:Glutathione Transferase; D004950:Esterases