الفهرس 
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Abstract
The Egyptian cotton leafworm S. littoralis, is considered as one of the most major and economic pest not only in Egypt, but also in many parts of the world such as Africa, Middle East and Turkey. The chemical controlling methods by insecticides is currently used inspite of their power of contamination, volatilization, bioaccumulation. The different groups of insecticides are considered the main factors affecting the agroecosystem (plant, soil, water and other organisms. from this point of view, it is necessary to minimize the application of insecticides which consider as the main source of environmental pollution and affected human health. There are many different insect species that have been successfully controlled by microbial agents and B. thuringiensis is considered highly beneficial for its specific activity.
The present investigation aimed to evaluate the efficiency of Dipel 2X (B.t. var. kurstaki) as biocontrol agent on the 4th instar larvae of S. littoralis.
The present study covered the following research points:
1- Effect of Dipel 2X at different concentrations (0.5, 1.0, 1.5 and 2.0%) on some biological parameters (%of larval mortality, larval and pupal durations, pupal weight, %pupation, %adult emergence, %sex ratio, adult longevity, fecundity, %fertility and %of malformed pupae and adults).
2- Effect of tested material at LC30 on the total fresh body weight, dry body weight and body water content.
3- Effect of tested material at LC30 on haemolymph volume and density.
4- Effect of B.t. var. kurstaki at LC30 on some biochemical parameters:
• The changes in the level of total soluble proteins, total lipids and total carbohydrates.
• Effect of tested material at LC30 on non specific esterases (- and -esterases).
• Effect of B.t. var. kurstaki at LC30 on alkaline and acid phosphatases.
• Effect of tested material on the activity of carbohydrate hydrolyzing enzymes (invertase, trehalase and amylase).
5- Effect of the tested microbial agent at LC30 on the total and differential haemocyte counts.
Obtained results can be summarized as follows:
1-Susceptibility of 4th larval instar of S. littoralis to different concentrations of B.t. var. kurstaki after 48 hrs of treatment:
Cumulative mortality percentage increased gradually with the increase in the concentration. It is quite clear from the recent results that the response of larvae to different concentrations of B t. var. kurstaki is represented by straight regression lines indicating homogenity. The LC30 and LC50 were 0.87 and 1.305%, respectively.
2- Impact of the tested microbial agents at different concentrations on some biological attributes of the 4th instar larvae of S. littoralis:
• The tested concentrations induced significant prolongation in the total larval duration comparing to control.
• There was an inverse relationship between the concentrations and the pupation percentages.
• It is clear from the obtained results that all of the tested concentrations induced significant reduction in the pupal weight.
• Highly significant increase in the pupal duration was observed at all tested concentrations.
• Insignificant decrease in the percentage of adult emergence was observed with an increase in the applied concentration. The sex ratio seems not to be affected by concentration of 1.5% since it always very close to 1:1.
• Dipel 2X at concentration of 2.0% caused the greatest reduction in the fecundity of the resulted female moth (964.5 eggs/female), whereas the tested material at 0.5% gave the lowest reduction (1552.5 eggs/female) as compared to (2142 eggs/female) in control group.
• The present data revealed that, the hatchability percentages of the deposited eggs decreased after treatment of 4th instar larvae with treated concentrations as compared to control.
• The obtained results and observations showed that deformations in pupae and malformations of adults were obtained after treated 4th instar larvae.
3- Effect of B. t. var. kurstaki at LC30 on the total body, dry body weights and on the body water content of the 4th instar larvae of S. littoralis:
• The total body weight of the treated larvae was significantly decreased at different time intervals under investigation (6, 12, 24 and 48 hrs) post-treatment. The same trends was also observed in the case of measuring the dry body weight.
• It is clear from presented results that the body water content was decreased significantly (p <0.05) at 6 hrs post-treatment, whereas highly significant decrease was recorded at the other three time intervals post-treatment. The decrease in the total body weight (fresh weight) after larval treatment with microbial agent appeared to be mainly due to the decrease in the dry body weight and secondary due to the decrease in the body water content.
4- Effect of microbial agent (B.t. var. kurstaki) at LC30 on the haemolymph volume and density of the treated larvae:
• The haemolymph volume was significantly decreased at 12, 24 and 48 hrs post-treatment. These values were 2.32±0.141, 1.56±0.194 and 4.68±0.245 l as compared to 2.71±0.111, 7.38±0.331 and 13.44±0.197 l, respectively.
• A significant increase in the haemolymph density was observed only at 12 hrs post-treatment. On the other hand, there is no significant differences in the values of haemolymph density in the untreated larvae as well as in treated larvae at 6, 24 and 48 hrs post-treatment.
5- Effect of tested material at LC30 on some biochemical parameters of S. littoralis treated as 4th larval instar:
• The total soluble protein contents in supernatant of the homogenated larvae post-treatment was generally decreased as affected by the tested material at different time intervals as compared to control.
• The total lipid contents in the homogenate of 4th instar larvae was significantly reduced when treatment carried out with LC30 of the tested material at different time intervals post-treatment. The decrease in the haemolymph lipids may be due to produce enzymes that utilize lipids to remove the invading agent.
• The total carbohydrate contents was significantly reduced and the reduction was (-14.9890, -43.33, -63.93 and -51.69%) with respect to control at the four different time intervals.
• The activities of - and -esterases were decreased in larvae treated with LC30 of Dipel 2X, and the reduction of enzymatic activity was highly significant.
• Alkaline phosphatase activity was highly significant reduced (p <0.01) at 6, 12 and 24 hrs post-treatment, whereas, the reduction of enzymatic activities at these periods were (-18.04, -50.33, -51.77 and -20.07%), respectively. The same significant reduction in the activity of acid phosphatase was also observed.
• Bacterial treatments induced inhibition in the enzyme activity of invertase where the values of inhibition were (-27.85, -5.92, -16.46 and -39.96%) at different time intervals of 6, 12, 24 and 48 hrs post-treatment, respectively.
• The percentages of reduction of trehalase enzyme activity of treated larvae was (-32.81, -12.95, -18.20 and -5.16%) at all inspected times (6, 12, 24 and 48 hrs), respectively. The corresponding figures of amylase were (-7.19, -42.63, -51.04 and -30.64%).
6- Effect of tested material at LC30 on the total and differential haemocyte counts of 4th larval instar of S. littoralis:
The mean of the total haemocyte counts in the treated larvae at all inspected times was highly significant increas The source of the added cells could be the mobilization of sessile haemocytes, production and release of haemocytes from haematobiotic organs, and/or the mitotic division of prohaemocytes.
• The present results and observations revealed that there was a marked variations in the haemocytes percentages of untreated and treated larvae of S. littoralis at different time intervals. In general, in the case of treated larvae an increase in the percentage of plasmatocytes and spherulocytes and decrease in the percentage of prohaemocytes, granulocytes and oenocytoids in the circulation were observed at all time intervals as compared to untreated larvae.