الفهرس 
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Abstract
-Comparison of toxicity levels of cotton leafworm field
population collected during 1978, 1979 and 1g8o cotton
growing seasons with ;those of a normal laboratory (susceptible)
strain was made. -The susceptibility of the second and fourth
instar larvae of the laboratory strain of Spodoptera littoralis
to sex insecticides was determined. Both larvae showed high
response to Decis, Ripcord, Sumicidin, Chlorpyrifos, Cyolane
and Cytrolane in descending order. When the dosages f or the
different ”\’Teight larvae were calculated as _)tg/ g . body weight,
it was found that the fourth instar larvae were more susceptible
to tested insecticides than the second instar larvae. The
second instar larvae were found to contai n high lipid content
than the fourth instar larvae. Therefore, the tolerance of
the second instar larvae may be due to their high lipid content.
The population of Kafr El-Sheikh strain acquired considera.ble
resistance to Chlorpyrif os (10.4 X) in the 1979 cotton
growing season. The resistance r atio of Chlorpyrif os decreased
to ( 6.3 X) in 1980. The resistance to Cyolane showed a l m-r
level of tolerance (4.8 X) durinr- 1978 and a 7. 2 X level of
tolerance in 1979. Concerning the resistance to Cytrolane
no significant detectable chanp:es were obs erved in resis t ance
ratio in 1978, 197g and 1980.
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J
In conclusion, Kafr El-Sheikh strain revealed crossresistance
or tolerance to the organophosphorus used,these
levels were 5.1, 4.8 and ’3. 9 fold in the 1978 season·; 1 0.4,
7.2, and 4.1 fold in 1979 season and 6.’3, 4.9 and ’3.5 fold
in the 1980 season for the following insecticides used Chlorpyrifos,
Cyolane and Cytrolane respectively Vith regard to
pyrethroid insecticides results revealed that the field strain
acquired alight level of tolerance to Sumicidin ’3.4 X in
1978 and a moderate level of tolerance 6.0 X in 1979, while
high level of tolerance 9.1 X was detected in 1980.Tolerance
to Ripcord increased from 1 .’3 X in 1978 to ’3.’3 X in 1979
followed by apparent DROP in resistance ratio 2.0 X at the
end of 1980.The same trend of slight increase in tolerance in
1980 cotton growing season was observed with Decis.
It is evident from the results presented here that the
use of different insecticides against Spodoptera littoralia
in a given area results in development of multiresistant or
multitolerant strains of this insect over this area.Also
these results revealed that in Kafr El-Sheikh Governorate
the choice should be given to Ripocord and Decis for the
control of the cotton leafworm.
The role of lipids and/or penetration as a mechanism of
insecticide-resistance or tolerance was studied.The results
revealed that the larvae of the field strain had a higher
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lipid content (1 .89 rg/g.body weight) than the larvae of the
laboratory strain (1.18 fg/g.body weight).Therefore, the
resistance or tolerance of the larvae of the field strain
might be due to their high lipid content.
The permeability of the insect intgument of both laboratory
and field strai~of Spodoptera littoralie was also studied by
comparing the insecticidal activity of the tested compounds by
injection and Topical application.Results revealed that the
adminstration of tested compounds by injection is generally
more effective than by topical application against both
straine.Aleo,the integument of larvae of the field strain
reduces the effectiveness of the tested insecticides by
decreasing the penetration of these insecticides.
It can be concluded that the cotton leafworm resistance
or tolerance may be related to their high lipid conte~t
and/or the·role of their integument in decreasing the penetration
of the tested insecticides.