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Memórias do Instituto Oswaldo Cruz
Fundação Oswaldo Cruz, Fiocruz
ISSN: 1678-8060 EISSN: 1678-8060
Vol. 90, Num. 3, 1995, pp. 411-413
Mem Inst Oswaldo Cruz. Rio de Janeiro, Vol. 90(3): 411-413, may/jun. 1995

Effects of Three Organophosphorus Insecticides in the Reproductive Potential of Culex quinquefasciatus

Lucita Aguilera, Maria del Carmen Marquetti, Agustin Navarro, Juan Bisset

Departamento de Control de Vectores, Instituto de Medicina Tropical "Pedro Kouri", Autopista Novia del Mediodia Km 6 No. 251, Apatlado 601 Zona 13, La Lisa, Ciudad de La Habana, Cuba

Code Number: OC95080
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A Culex quinquefasciatus Say 1823 strain with resistant genes to organophosphates was tested in the laboratory to know the reproductive potential after exposure, as larvae, at the LC^30 and LC^70 (mg/l) of three organophosphorus insecticides: malathion, chlorpyrifos and methyl-pirimiphos. Data showed that fecundity was decreased significantly by malathion at LC^30= 0.0025 and LC^70= 0.0075, whereas fertility had a no significant decrement by chlorpyrifos and methyl-pirimiphos at the LC^70 (0.000016, 0.00043). The sexual index was affected by chlorpyrifos and methyl-piritniphos showing a greater number of adult females.

Key words: insecticide - malathion - chlorpyfifos - methyl-pirimiphos - reproduction - Culex quinquefasciatus

In 1981 Cuba started an intensive campaign for the control of mosquito Aedes aegypti (Linnaeus) (Diptera: Culicidae). The insecticide more used between 1981 and 1986 was malathion, in addition, temephos and fenthion were also used. In 1986 began the use of other organophosphorus insecticides like methyl-pirimiphos and chlorpyrifos. This campaign reached success in the control of A. aegypti, but at the same time Culex quinquefasciatus, as a secundary effect, began the colonization of the typical urban breedingsites of that species (Bisset et al. 1987), increasing their populations in spite of the continuous use of insecticides in those areas, suggesting the presence of resistance in this mosquito (Bisset & Marquetti 1983). The treatment of a determinate species with sublethal doses of insecticides may affect their survival, their reproduction or the genetic composition of future generations (Moriarty 1969). Hunter (1958), working with the malathion and diazinon found a reduction of Musca domestica descent, while El-Khatib and Geroghiou (1985) reported that the treatment of C. quinquefasciatus larvae with temephos decreased the fecundity of survivors. These reports indicate that the sublethal effects of the pesticides can be important for the reduction of the number of injurious insects in pest control programs.

The present work describes the effect of the sublethal doses of three organophosphorus insecticides on the reproductive potential of C. quinquefasciatus.

MATERIALS AND METHODS

A strain of C. quinquefasciatus denominated "quibu" was used. It was mantained in standard conditions of laboratory (25 + 2 C and 75 + of relative humidity) and free of insecticides for ten successive generations. In one liter 'of distilled water five rafts of eggs were placed. Larvae were fed daily with fishmeal. Pupae were transferred to a beaker containing water and placed in a breeding box.

Adults mosquitoes were blood fed on chicks three days after emergence and offered a sugar solution on cotton pads as a carbohydrate source.

Insecticides tested were malathion (95% TG), chlorpyrifos and methyl-pirimiphos (90% TG) and ethanol was used as solvent. Three tests were done for each insecticide and, each test consisted of five concentrations of chemical, using five replicates for concentration. Controls for each insecticide were used and treated with ethanol. Twenty five larvae were placed into glass flasks containing 200 ml of distilled water and were exposed to the insecticide for 24 hr without food. Survivor larvae were washed and put in distilled water, offered daily fishmeal and were maintained in trays until they reached the pupal stage.

Pupae were sexed for each insecticide and concentration, and 100 male pupae and 100 female were placed in breeding boxes, for each dose of each insecticide and for the control. After the coupling of the adults, rafts of each box were collected up to a number of fifty.

Eggs were counted in the rafts obtained per insecticide and concentration, and the percent eclosion was recorded. The emergent larvae were placed into trays until they reached the pupal instar and these were finally sexed to establish the sexual index for each insecticide and concentration.

Data of bioassays were submitted to a computer program called probit-log (Raymond 1985). The ANOVA test of Linear Regression, the Kruskal-Wallis and Student-Newman Keul tests and the test for the comparison of two proportions were also used. It was considered significant at the level of p < 0.05.

RESULTS AND DISCUSSION

The toxicity of the three tested insecticides on larvae of early fourth stage of C. quinquefasciatus, is shown in Table I. From this ,Table is observed that chlorpyrifos was the most toxic (LC -0.000009 mg/l) followed by methyl- pirimiphos (LC50=0.00026 mg/l) and maolathion (LC50=0.0035 mg/l). These values of LC50 are in accordance to those previonsly reported by Villani et al. (1983) and El-Khatib and Georghiou (1985), who worked with malathion and chlorpyrifos insecticides.

In Table II the effect of these insecticides on the fecundity of C. quinquefasciatus is shown. In the survivors at LC30 and LC70 of malathion, the production of eggs was reduced to 57% (p C. pipiens and C. quinquefasciatus larvae exposed to different organophosphorus insecticides. On the other hand, Ferrari and Georghiou (1981) reported a significant reduction in the fecundity of C. quinquefasciatus when the larvae were exposed to the organophosphate temephos.

The fertility of the eggs was not affected in the treated larvae with malathion, whereas it was observed a slightly reduction, p > 0.05, in larvae exposed at the LC70 of chlorpyrifos and methylpirimiphos. This is consistent with previous studies which reported that expositions to malathion of larvae of A. aegypti did not result in a reduction of the fertility of eggs (Firstenberg & Sutherland 1981, Ferrari & Georghiou 1981, Robert & Olson 1989).

The pupation time had a significant increase (p< 0.05) for all concentrations of the insecticides tested. The male mosquitoes exposed to the insecticides had an emergence time slightly longer than the controls, however it was increased significantly (p< 0.05) at the LC30 of malathion. The females exposed as larvae at the LC30 of malathion and methyl-pirimiphos also had a significant longer time of emergence (p< 0.05) than the controls. The increase of the larval and pupal periods that resulted from treat-ments with insecticides are in accordance to the results obtained by Wijeyaratne (1976) and Robert and Olson (1989). Larval prolonged development has been reported by Farghal (1979) with various doses of other insecticides in C. pipiens auto- genic.

The sexual proportion in adults was affected by exposition to chlorpyrifos and methylpirimiphos. So, in larvae treated with these insecticides the quantity of adult females had a significant increase (p< 0.01). However this was not observed in larvae treated with malathion where the sexual proportion was not affected. Robert and Olson (1989), working with the same species, found a reduction of the proportion of females coming from larvae exposed to metho- prene, propoxur and resmethrine, whereas Farghal and Temerak (1981) found gradual increments of female proportion, accompanied by gradual increments of concentrations of metho- prene. Martinez-Mole (1991) working with the same species found that sublethal doses of cipermethrine did not produce any change in the female-male proportion.

CONCLUSIONS

From three tested insecticides in "quibu" strain of C. quinquefasciatus, it was demostrated that chlorpyrifos was the most toxic, followed by methyl-pirimiphos and malathion.

A reduction of the fecundity in the studied species was found when it was pressed with malathion doses, whereas the fertility decreased with doses of chlorpyrifos and methylpirimiphos.

The sexual index in the studied species was affected with exposure periods of methylpirimiphos and chlorpyrifos, but not with malathion.

TABLE I

Values of LC50 and LC90 (mg/l) of Culex quinquefasciatus larvae exposed to three organophosphorus insecticides

-------------------------------------------------------------
Insecticide  LC50 Fiducial limit  LC90  Fiducial limit Slope
-------------------------------------------------------------
Malathion    0.0035 0.003-0,004  0.0075  0.007-0.008  9.8 
Chlorpyrffos 0.000009 0.000007-0.00001 0.00004 0.00003-0.00005 
                                                      1.97 
Methyl-   0.00026 0.00023-0.00028 0.00089 0.00079-0.00103 2.39

pirimiphos
--------------------------------------------------------------

TABLE II

Effect of three organophosphorus insecticides on the fecundity of Culex quinquefasciatus

--------------------------------------------------------------
                                Total egg    Egg proportions 
Insecticide                     production   in relation 
                                             to the control
--------------------------------------------------------------
Malathion 
LC30 (0.0025)                    7.036          0.57a 
LC70 (0.0075)                    6.281          0.51a 
Control                          12.181         1.00 
Chlorpyrifos 
LC30 (0.000004)                  12.109         0.90 
LC70 (0.000016)                  11.458         0.94 
Control                          12.181         1.00 
Methyl-pirimiphos 
LC30 (0.00015)                   11.492         0.94 
LC70 (0.00043)                   10.005         0.82 
Control                          12.181         1.00
-------------------------------------------------------------

a: values that are different for p<0.05, in relation to the control

REFERENCES

Bisset J, Marquetti MC 1983. Compoflamiento relativo de las densidades larvales de Aedes aegypti y Culex quinquefasciatus durante la etapa intensiva de la campana anti-aegypti. Rev Cub Med Trop 35: 176-180.

Bisset J, Gonzalez B, Mendizabal ME, Marquetti MC, Navarro A 1987. Algunos aspectos del nicho ecol6gico de Aedes aegypti y Culex quinquefasciatus en el ambiente tubano. Rev Cub Med Trop 39:113-118.

El-Khatib ZI, Geroghiou GP 1985. Geographic variation of resistance to organophosphates, propoxur and DDT in the soulher house mosquito, Culex quinquefasciatus in California. J Amer Mosq Cont Assoc 1: 279-283.

Farghal AI 1979. Recent studies in culicine mosquito control. Ph.D. Thesis. Assuit University Egypt.

Farghal AI, Temerak SA 1981. Effect of the juvenile hormone analogue Altoaid on some culicine moaquitoes and their associated insects under field and laboratory conditions. Z Angew Entomol 92: 505-510.

Ferrari AI, Georghiou GP 1981. Effects of insecticidal selection and treatment on reproductive potential of resistance susceptible and heterozygoos strains of the Southern house mosquito. J Econ Entomol 74: 323-327.

Firstenberg DE, Sutherland DJ 1981. Reproductive effects in Aedes aegypti following sublethal treatment with methoprene or abate. Proc N J Mosq Cont As soc 68th Annu Meet 68: 47. Hunter PE 1958. Reproduction in DDT and Diazinon treated house flies. J Econ Entomol 51: 579-582.

Martinez-Mole M 1991. Efecto de la cipermetrina sobre algunos factores reproductivos en Culex quinquefasciatus Say 1823. MSc Thesis. Inst Med Trop "Pedro Kouri".

Moriarty F 1969. The sublethal effects of synthetic insecticides on insects. Biol Rev 44: 321-357.

Raymond M 1985. Presentation d' un programe d' analyse log-probit pour micro-ordenateur. Cah-OR- STOM Sdr Ent Med et Parasitol 22:117-121.

Robea LL, Olson JK 1989. Effects of sublethal dosages of insecticides on Culex quinquefasciatus. J Amer Mosq Cont Assoc 5: 239-246.

Villani F, White GB, Curtis CF, Miles SJ 1983. Inheritance and activity of some esterases associated with organophosphate resistance in mosquitoes of the complex of Culexpipiens. L Bull Res 73: 153-166.

Wijeyaratne PM 1976. Effects of sublethal larvicide exposure on population and flight characteristic of Culex pipiens quinquefasciatus. Ph.D. dissertation. Univ of Texas Health Science Center at Houston, 245 pp.

Copyright 1995 Fundacao Oswaldo Cruz

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