LT50 of malaria vectors against insecticides used in district Muzaffargarh, Pakistan

Muzaffargarh is an endemic area for malaria where An.culicifacies is the main malaria vector and Anopheles stephensi (Liston) is the secondary vector. We determined the susceptibility and irritability levels of field strains of both the species to discriminative dose of different insecticides against their adult stages based on World Health Organization’s (WHO) established criteria. On performing probit analysis, An.stephensi was found resistant to DDT (dichlorodiphenyltrichloroethane, an organochlorine), dieldrin (a chlorinated hydrocarbon), and malathion (organophosporus) with Lethal Time 50 (LT50) of 83.17 (p= >0.05, CI: 78.50-87.80), LT 50 of 52.48 (p= >0.05, CI: 49.30-55.66), and LT50 of 37.53 (p= >0.05, CI: 33.45-41.59), respectively. The species found sensitive to permethrin, deltamethrin and fenitrothion (all pyrethroids) with LT50 of 2.85 (p= <0.05, CI: 2.21-2.85), LT50 of 2.34 (p= <0.05, CI: 1.98-2.70), and LT 50 of 13.18 (p=<0.05, CI: 11.18-15.17), respectively. Among these, permethrin showed more promising results against adult An.stephensi along with the other two drugs.

When analysed for irritancy, we found that among pyrethroids permethrin had the most irritant for An.stephensi and An.culicifacies. Both the DDT and dieldrin showed the least irritant for An.stephensi with 0.42 ± 0.08 and 0.77 ± 0.12 take-offs/min/adults, respectively.

The mean number of take-offs/min/adult with permethrin showed significant irritancy for permethrin when compared with DDT. Pyrethroid insecticides are being used as indoor residual sprays in Pakistan. Based on this study, we conclude that use of organochlorine (DDT) and chlorinated hydrocarbon (dieldrin) must not be reintroduced at any stage in future, and the use of pyrethroids should continue with preference given to permethrin for effective control of malaria by indoor spraying technique

 

Key words: An.culicifacies, An.stephensi, insecticides, irritancy, susceptibility