الفهرس 
MATERIAL AND METHODOnly 14 pages are availabe for public view
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Abstract
(synthetic pyrethroids) insecticides and pyriproxyfen (insect growth regulator). The insecticide
pressure was performed for I 0 generations. All experiments were maintained at laboratory
conditions of 27± 2 and 80±5 %R.H.
!-Build up of susceptible-laboratory strain.
The obtained data revealed that the LC50 values of the two investigated insecticides were
decreased by succession of generations. A sharp decrease in LCso values was noticed at F 18 and F21
with both insecticides. The recorded values of fenitrothion were 0.052, 0.0056, 0.0037 and 0.0013
ppm for parent, Fl5, Fl8 and F21 respectively, while these values were 0.035, 0.011, 0.0056 and
0.0011 ppm for cyphenothrin. It is clearly evident to notice that the LC50 of F21 line was steeper
than other lines representing the forward generations. This means that there is a high degree of
strain homogeneity toward susceptibility to both offenitrothion and cyphenothrin.
2-Development of resistance to fenitrothion.
Data indicated that the homogeneity of individuals toward resistance to fenitrothion was increased
pronounccdly by generations progression. The LC5o values were 0.052, 0.497, 7.332, 10.52
and
12.148 ppm with P, Fl, F4, F7 and FlO, respectively. The slope values
of regression lines were increased in F l and F4 generations, while clear decrease was observed in
F7 and FlO, but continued higher than parent strain. The slope values were 1.365, 2.476,
2.105, 1.966, and 1.875 for P, Fl, F4, F7, FlO, respectively. On the other hand, the level of
resistance was increased from 40 fold at parent generation to 382.3, 5640, 8100 and 9372.3 fold
at Fl, F4, F7 and FlO generations, respectively. from these data one may notice clear development
of fenitrothion resistance.
3-Development of resistance to cyphenothrin.
The LC50 values of cyphenothrin-tested generation were increased when compared with parent
strains, it reached 0.035, 0.383, 5.643, 7.913 and 10.272 ppm for parent, Fl, F4, F7 and FlO,
respectively. In addition the slope values of ld-p lines of selected
successive generation increased gradually than the parent line till the I O’h generation. The
recorded slope values were 1.83, 1.98, 1.96 and 1.99 for Fl, F4, F7 and FlO, respectively, while
the slope values for parent was 1.71. The calculated resistance ratio confirmed the development of
resistance across the selective generation, thus the level of resistance increased progressively as
the generation proceeded. The recorded values were 31.8, 348.2, 5138, 7193.6 and 9358.2 fold for
parent, Fl, F4, F7 and F I 0, respectively.
4-Development of resistance to pyriproxyfen.
The obtained data revealed that the LC50 value for pyriproxyfen was 0.0091ppm compared with
0.0009ppm for susceptible strain. The slope values reached 0.98 and 3.83 for parent and susceptible
strain, respectively. It was noticed that the treatment of 4’h instar larvae of parent colony
with pyriproxyfen at LC30 as a selective pressure agent caused I 00% mortality of pupal stage
resulted from survived larvae. On the other hand, the larvae failed to complete their life cycle.
This finding could be attributed to the latent effect of this insect growth regulator. Thus we
could not obtain resistance strain from these parent
colony of culex pipi ens by exposure of larval strain to selective pressure of pyriproxyfen.
5-Cross-resistance spectrum in fenitrothion and cyphenothrin-selected strains.
1- fcnitrothion-sclcctcd strain.
The obtained results revealed that the (JHM), pyriproxyfen and the two pyrethroids deltamthrin and
cyphenothrin were more toxic to the 41h instar larvae offenitrothion-resistant strain than the
other tested op’s, malathion and diazinon. The LC50 values were 0.853, 0.861, 1.00 I, 7.62 and 9.00
ppm, receptively. However the LC50 of fenitrothion was 12.184 ppm. The rate of toxicity indicated
that the (JHM) pyriproxyfen was more toxic by 14.28 times. Deltamthrin showed the almost the same
degree of toxicity as pyriproxyfen, followed by cyphenothrin, malathion and diazinon, showing
14.15, 12.17, 1.59 and 1.35 times as fenitrothion.
The data further provided evidence that fenitrothion-resistant strain showed wide cross-resistance
with all of the tested insecticides. But the pyrethroids and JHM recorded about tenth the level of
resistance of fenitrothion.
2- cyphcnothrin-sclcctcd strain.
The obtained results revealed that the (JHM) pyriproxyfen was the most toxic compound against the
larvae of cyphenothrin-resistant strain of Culex pipiens (L.). The tested organophosphorus
diazinon, malathion and fenitrothion showed almost similar LC5o values and followed pyriproxyfen
activity. The LC50 values were 0.80 I, 0.991, 1.00I and 1.118 ppm for pyriproxyfen, diazinon,
malathion and fenitrothion respectively. The pyrethoid deltamthrin showed lowest toxic effect than
the other tested insecticides. The recorded LC5o was 8.302
ppm, while LC50 of cyphenothrin was 10.272 ppm. There was no significant difference between these
values. Data also indicated that there was a significant difference between LC50 of
pyrethroid group,
JHM and organophosphorus compounds. The rate of toxicity indicated that pyriproxyfen was more toxic
by 12.82 times. Diazinon showed almost the same degree of toxicity as pyriproxyfen, followed by
malathion, fenitrothion and deltamethrin, showing 10.37, 10.27, 9.19 and 1.24 times as
cyphenothrin, respectively.
The recorded resistance level values were 860, 888.8, 910, 940 and
9224.4 fold for fenitrothion, pyriproxyfen, malathion, diazinon and deltamethrin, respectively.
While the level of cyphenothrin-resistant strain was 9338.2 folds. This data indicated that the
developed resistance strain showed wide resistance spectrum to the tested insecticides.
6-Resistance spectrum of certain Field population of
Culex pipiens larval stage.
The susceptibility of 41
instar larval stage collected from
Shalakan (Qalubiya govemerate) to certain insecticides was investigated. It could be seen that
the JHM pyriproxyfen was the highest effective compared with the other tested insecticides.
Dcltamcthrin showed almost the same degree of toxicity as pyriproxyfen. Statistical analysis
revealed that there was insignificant difference between the LC50 values of pyriproxyfen
and deltamethrin, i.e. 0.008 and 0.0099 ppm, respectively. Cyphenothrin and malathion showed
almost the same LC50 values and followed pyriproxyfen and deltamethrin. The LC50 ’s were
0. l 02 and
0. l 03 ppm for cyphenothrin and malathion, respectively. Fenitrothion
and diazinon showed almost the same and lowest degree of toxicity. The LC50 for these compounds
were 0. l I and 0.12 ppm, respectively. There was insignificant difference between the
LC50 of the last four
insecticides. The lowest resistance level was recorded with pyriproxyfen
(8.8 fold), followed by deltamethrin ( l l fold). However, the other tested
insecticides showed high level of resistance, and could be an·anged in
ascending order as: fenitrothion (84.6 fold), cyphenothrin (92.7 fold), malathion (93.6 fold) and
diazinon ( 120 fold).
The sensitivity of larval stage of Culex pipiens collected from
EL-Suff was studied. Cyphenothrin proved to be the lowest toxic compound than the other
insecticides. Pyriproxyfen proved to be the most effective insecticides followed by
deltamethrin, malathion, fenitrothion, diazinon and cyphenothrin, showing LC50 ’s of0.009, 0.011,
0.1 00, 0.1 07, 0.112 and 0.122 ppm, respectively.
?-Susceptibility of certain field population and resistant strains of Culex pipiens females to
tested insecticides.
The sensitivities of Shobra EL-Khema populations, fenitrothion R and cyphenothrin-R strains of
Culex pipiens females to malathion, fenitrothion, diazinon, cyphenothrin and deltamethrin were
measured. The standard discriminating dosage and exposure time according to the protocol suggested
by WHO (I998) was followed in this investigation. The sensitivity of susceptible strain was taken
as a reference for companson.
Data revealed that deltamethrin and cyphenothrin (pyrcthroids)
recorded the lowest knock down effects’ i.e. 8 and 17.5 for deltamethrin and cyphenothrin,
respectively. On the other hand, these compounds recorded in general the highest killing effects,
showing 95 and 79% mortality for these two insecticides, respectively in Shobra EL-Khema.
The knock down effect of the tested organophosphorus compounds could be arranged in ascending order
as fenitrothion (20%), followed by malathion (25%) and diazinon (35%). However the killing effect
of these compound were arranged ascending as fenitrothion (72%), malathion (75%) and diazinon
(80%).
Data in concern of the response of cyphenothrin-resistant strain
to tested insecticides. The deltamethrin achieved the lowest knock down effect (I 0%), followed
by cyphenothrin ( 15%), diazinon (25%),