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Memórias do Instituto Oswaldo Cruz
Fundação Oswaldo Cruz, Fiocruz
ISSN: 1678-8060 EISSN: 1678-8060
Vol. 89, Num. 2, 1994, pp. 251-252
Mem. Inst. Oswaldo Cruz, Rio de Janeiro, Vol. 89(2): 251-252, apr./jun. 1994


RESEARCH NOTE


Susceptibility Status of Aedes taeniorhynchus to Organochlorine and Organophosphate Insecticides

Domingo Montada, Rosa Tang, Agustin Navarro, Francisca A Garcia


Code Number: OC94052
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Instituto de Medicina Tropical "Pedro Kouri", Autopista Novia de Mediodia, Km 6, e/ Autopista Nacional y Carretera Central, Apartado 601, Lisa, Ciudad de la Habana, Cuba

Key words: Aedes taeniorhynchus - susceptibility - organochlorine - organophosphate


Aedes taeniorhynchus play an important role in the transmission of Eastern Equine Encephalomyelitis (EEE), an important medical- veterinary arbovirus. A Fernandez et al. (1973 Rev Cub Hig Epid 19: 35-40) isolated EEE virus from Ae. taeniorhynchus in Havana, incriminating it as a vector and demonstrating its involvement in arbovirus transmission. Chemical control strategies against Ae. taeniorhynchus are very important to control vector populations and transmission of EEE. However, it is first necessary to determine the susceptibility status of vector population to various insecticides. Hence, we reported data on this subject using organophosphorus (5) and organochlorine (1) insecticides.

Larvae susceptibility tests in the laboratory followed the WHO procedure (WHO/VBC 81.807) using stock solutions of malathion, fenthion, fenitrothion, temephos, chlorpyrifos and DDT obtained from WHO. Late-third or early-fourth instar of Ae. taeniorhynchus larvae, collected in Rosario Beach, Guines, Habana Province were used. Eight tests were done for each insecticide. Each test consisted of four replicates each of six concentrations obtained by serial dilutions from each solution. Water used in the tests was obtained from inmature habitats and ranged from 10-12 mg/l salinity (pH values ranged from 7.5 to 8.0 and were not significantly different).

Tests were conducted with mosquito samples collected during the rainy (May-October) and dry (November-April) seasons.

LC50 and LC90 values were calculated by probit analysis (M Raymond 1985 Cahiers ORSTOM 23: 117-121). Control mortality was corrected using Abbott's formula (WS Abbott 1925 J Econ Entomol 18: 265-267). Replicates with larval mortality > 20% were discarded and repeated. All tests were conducted under laboratory conditions at 26 +/- 1 oC.

LC50 and LC90 values are shown in the Table. Ae taeniorhynchus was more susceptible to chlorpyrifos than the other insecticides tested. According to the WHO procedure, above mentioned, we found the following discriminating doses to chlorpyrifos (0.008 mg/l); DDT (0.02 mg/l); fenthion (0.02 mg/l); fenitrothion (0.04 mg/l); malathion (1.0 mg/l) and temephos (0.008 mg/l). LC50 and LC90 values reported here for fenthion and malathion insecticides are very similar to those found by AH Boike et al. (1978 Mosq News 38: 210-217) using a susceptible strain from Florida, U.S.A.

Discriminating insecticide dosages for Ae. taeniorhynchus obtained here, for the first time in Cuba, provide baseline data for monitoring the development of resistance to those insecticides used against this mosquito.

TABLE

Susceptibility of Aedes taeniorhynchus larvae to organochlorine and organophosphate insecticides collected in Habana Province, Cuba, 1991-1992

===================================================== Insecticides 95% Fiducial limits for LC 50 LC 90 LC 90 (mg/l) (mg/l) LCL UCL ------------------------------------------------------ Chlorpiryfos 0.00043 0.00107 0.00093 0.00129 DDT 0.00172 0.00352 0.00318 0.00400 Fenthion 0.00131 0.00318 0.00281 0.00373 Fenitrothion 0.00149 0.00441 0.00377 0.00533 Malathion 0.02588 0.09535 0.08260 0.11366 Temephos 0.00068 0.00152 0.00136 0.00173 ------------------------------------------------------ Insecticides Regression ------------------------------------- Equation F F Chi^2 ------------------------------------------------------ Chlorpiryfos 5.16 + 3.2 lnX 12.90*** 9.37 DDT 5.33 + 4.1 InX 153.61*** 4.38 Fenthion 5.26 + 3.3 InX 11.52*** 5.84 Fenitrothion 5.22 + 2.7 InX 25.26*** 8.64 Malathion 5.63 + 2.2 InX 123.19*** 8.94 Temephos 5.12 + 3.6 InX 6.14** 5.44 =====================================================

Copyright 1994 Fundacao Oswaldo Cruz - FIOCRUZ

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