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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
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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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Text: 14K
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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 = 0.05) and 59% (p =
0.05), respectively, as compared with the control. However,
the fecundity was not affected in the survivors at the LC30
and LC70 of chlorpyrifos and methyl-pirimiphos. Similar
results were reported by Wijeyaratne (1976), El-Khatib and
Georghiou (1985) and Robert and Olson (1989) for 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
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Copyright 1995 Fundacao Oswaldo Cruz
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