الفهرس 
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Abstract
The extensive use of synthetic pesticides has led to the development of resistance to the pests, environmental pollution,
residual effects and adverse effects on human and animal health.
These problems forced to search for new control measures
especially from plant sources. Among these strategies are the use
of essential oils, where plant essential oils are selective and have
little or no harmful effects on the environment and non-target
organisms. The present study was designed to evaluate the
larvicidal, physiological, histological and ultrastructural effects of
the essential oils of garlic and lemon on the Egyptian cotton
leafworm, Spodoptera littoralis 4th instar larvae.
Both garlic and lemon oils showed larvicidal effects against
S. littoralis 4th instar larvae, with LC50 and LC30 of 19.95 and
16.60% for garlic oil, respectively; 24.20% and 20.09 % for
lemon oil, respectively. Treatment of S. littoralis 4th instar larvae
with the LC30 of garlic and lemon oils resulted in antifeeding
activity, with highest magnitude for garlic oil. This is also true for
the percentage of starvation. Where, the percentage of starvation
in garlic-treated larvae was about 3-times more than that of larvae
treated with lemon oil.
The effect of garlic and lemon oil treatment (LC30) on the
nutritional indices of S. littoralis larvae was also studied. The
consumption index, which is a measure of the amount of food
eaten per unit time relative to the mean weight of larvae during the feeding period; the relative growth rate, which measures the
amount of weight gained per unit time relative to the mean weight
of larvae during the feeding period; and the approximately
digestibility, which measures the ability of the larvae to digest the
introduced food (absorption capacity) were decreased due to
treatment with garlic and lemon oils throughout the larval
duration. In contrast, food utilization, in terms of the efficiency of
conversion of both ingested and digested food to biomass
increased due to such treatment throughout the larval duration. In
all these metabolic parameters, the effects of garlic oil were
higher than those of lemon oil.
Biochemical analyses showed that garlic and lemon oils
(LC30) decreased the total protein and lipid content in larvae
compared to the non-treated larvae. Whereas, this treatment
increased the total carbohydrate content. However, both garlic and
lemon oil declined the activity of α-amylase and lipase.
Protein electrophoresis revealed that treatment of S. littoralis
4th instar larvae with the LC30 of garlic and lemon oils had
inhibitory effect, where there were 3 and 2 protein bands,
respectively compared to 5 bands for the control. The protein
band of the molecular weight of 50.8 KDa was common in treated
and non-treated groups. This band seems to be the major protein
band of S. littoralis larvae.
Histologically, the main histological changes in S. littoralis
larvae treated with the LC30 of garlic and lemon oils were vacuolation of the cytoplasm of the columnar cells, necrosis of the
columnar and goblet cells and clumping of the chromatin
materials of the nucleus. Ultrastructurally, this treatment
disorganized the organelles particularly the mitochondria. Also,
treatments showed induction of the occurrence of numerous
lysosomal bodies, autophagic vacuoles, vacuolation in the
cytoplasm of columnar and goblet cells and of clumping of the
nuclear chromatin.
In conclusion, it appears that garlic and lemon oils are safe
and potential agents for controlling S. littoralis larvae.