الفهرس 
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Abstract
The cotton leafworm, Spodoptera littoralis (Boisd.) is considered one of the most harmful insectal pests in Egypt. It causes major damage to cotton plants as well as more 29 hosts from other crops and vegetables. The environmental hazards of conventional insecticides necessitate introducing of alternative groups that are effective, safe to human and ecosystem. The present study was carried out at Itay El-Baroud Agricultural Research Station during 2018 season to investigate the toxicity of Grand®, Roxy®, speedo®, Biolarve®, Rider®, and Rildan® against 2nd and 4th larval instars of cotton leaf worm, S. littoralis (Boisd.) and their effects on certain enzymes of the worm under laboratory conditions. Also, to demonstrate the efficiency of examined insecticides in association with esterases and GST activities. Synthetic insecticides differ in their mode of actions For example, emamectin benzoate cause inhibition in muscle contraction, resulting in continuous flow of chlorine ions in the Gama Amino Butyric Acid (GABA) and H-Glutamate receptor sites. . The main mode of action of Indoxacarb is via blocking of neuronal sodium channels. It is fairly lipophilic with a Kow of 4.65. This pesticide should be used with caution since some insects such as S. littoralis become resistant when exposed. Chloropyriphos-methyl is an insecticide which is active by contact, ingestion, and vapor action, and causes phosphorylation of the acetylcholinesterase enzyme(AChE) of tissues, allowing accumulation of acetylcholine (ACh) at cholinergic neuro-effector junctions. Insect growth regulator (IGR) is considered safe alternative to the cynthetic insecticides that reduce the invironmental hazared. IGR such as novaluron and lufenuron (Benzoylphenyl ureas) has a large effects in inhibition the production of Chitin in the insects. Without chitin, Lepidopterans larvae will never develop a hard-outer shell (exoskeleton). There for the present study aims to: 1- Investigate the toxicity of Grand®, Roxy®, Speedo®, Biolarve®, Rider®, and Rildan® on 2nd and 4th larval instars of the cotton leafworm, S. littoralis (Boisd.) and their effects on larvae under laboratory conditions. 2- Demonstrate the efficiency of the examined insecticides in association with esterases and GST activities. 3- Assay of some biochemical compounds e.g. Alanine amino transferase (ALT), Aspartate amino transferase (AST) and total protein in insect homogenate. The obtained results could be summarized as follows: 5.1. Insecticide efficacy: To determine the lethal concentration of 50 and 90 % of the 2nd and 4th instar larvae of the field and lab. strains of cotton leafworm, the larvae were exposed to the treated leaves with a wide range of insecticide concentrations used in this study (Rider®, Reldane®, Biolarve®, Speedo®, Roxy®, and Grand®). The examined insecticides exhibited potential toxic on lab. strain greater than field strain. As for, LC50, LC90 slope and index for the six insecticides Speedo®, Rider®, Biolarvae®, Grand®, Roxy® and Reldan® against 2nd instar of S. littoralis these compounds were tested on tow strains (lab. and field strains) collected from Etay- El-Barod. Data showed that insecticide, Speedo® was very toxic, where it had the laest LC50: 0.22 and 0.89 ppm on the 2nd instar larvae of lab. and field strain respectively. In the contrast of this Reldan insecticide seemed to be low toxic to the 2nd instar larvae of both lab and field strains. It had the highest LC50 values with averages of 35.17 and 45.57 ppm to lab and field strains respectively, compared with the all insecticides on the two strains. In the same line, Speedo® was the most effective insecticide against S. littoralis 4th instar larvae of lab and field strains, where it exihibted the laest LC50 0.41 and 1.71 ppm to both lab and field strains respectively. On the other hand Reldan® was had the laest effective in reducing of S. littoralis 4th larval instar in both lab and field strains. It showed LC50 with averages of 42.06 and 134.24 ppm in both lab and field strains, respectively. When calculated the RR the values were from 1 to 6 for the all insecticides. RR was low resistance for Speedo®, Rider®, Grand®, Roxy®, and Rildan®, erspectively. The RR values were 4.17, 3.11, 3.91, 2.16, 2.47 and 3.15 for Speedo®, Rider®, Biolarvae®, Grand®, Roxy, and Reldan® respectively. 5.2. Biochemical Responses. 5.2.1. Acetylcholinesterase (AChE) . The examined insecticides induced decrease in AChE activity in the homogenate of the two strains of S. littoralis compared with the control. Reldan® induced the greatest decrease in enzyme activity; 0.28 and 0.34 μmol/mg/min on field and lab. strain, respectively, followed by Biolarve® (0.39 and 0.40 μmol/mg/min), and Speedo® (0.43 and 0.39 μmol/mg/min). Roxy® was the least potent to decrease enzyme activity; 0.57 μmol/mg/min compared with the control; 60 μmol/mg/min on field strain. 5.2.2. Esterases The examined insecticides induced alterations in esterase’s activities in lab. and field strain of S. littoralis as illustrated in α-esterase significantly increased in lab. strain than in field strain. The all insecticides exhibited values lower than the control (1.43 μmol/mg/min) as observed in the order: 0.14, 0.38, 0.90, 0.94, 0.84, and 0.95 μmol/mg/min in lab. strain, for Rider®, Reldane®, Biolarve®, Speedo®, Roxy® and Grand®, respectively. Insecticide, Speedo® induced the greatest inhibition in larval homogenate of field strain (0.04μmol/mg/min) compared with the control; 0.19 μmol/mg/min. However, Rider® induced the greatest inhibition; 0.14 μmol/mg/min in the larval homogenate of lab. strain. Regarding β-esterase, all insecticides induced inhibition in larval homogenate of field strain greater than the control (0.42 μmol/mg/min) with values; 0.25, 0.08, 0.005, 0.10, 0.08 and 0.15 μmol/mg/min for Rider®, Reldane®, Biolarve®, Speedo®, Roxy® and Grand®, respectively. However, the all tested insecticides on the lab. strain showed activities greater than control (0.16 μmol/mg/min), except Rider® and Grand® which induced inhibition in larval homogenate lower than the control with activities 0.03 and 0.15 μmol/mg/min, respectively. The least effect was recorded for Biolarve® (0.43 μmol/mg/min). 5.2.3. Glutathione-S-transferase (GST). The examined insecticides induced changes in the enzyme activity in the larval homogenate of lab. and field strain of S. littoralis. The activities in field strain were greater than the control (51.50 nmol/mg/min) with values; 22.50, 15.00, 16.50, 15.50, 14.00 and 20.50 nmol/mg/min for Rider®, Reldane®, Biolarve®, Speedo®, Roxy®, and Grand®, respectively. Regarding lab. strain, insecticides induced an increase in enzyme activity greater than the control (31.50 nmol/mg/min), except Rider® and Grand® (9.00 and 14.50 nmol/mg/min). Reldane® induced the greatest activity, 42.00 nmol/mg/min. 5.2.4. Alanine aminotransferase (ALT)/ Aspartate aminotransferase (AST). In field strain, ALT activities were greater than the control (66.80 U/L), with values; 74.97, 85.93, and 71.93 U/L for Rider®, and Grand®, respectively. Regarding lab. strain, the activities were 41.18, 40.68, 30.89, 19.58, 10.03 U/L for Rider®, Reldane®, Speedo®, Roxy®, and Grand®, respectively. Biolarve® induced the least activity, 61.00 U/L compared with the control which did not exceed 46.13 U/L. Activities of AST enzyme in laboratory and field strains were lower than the control. The activities were in the following order: 16.72, 11.22, 11.44, 19.11, 30.58 and 26.81 U/L for Rider®, Reldane®, Biolarve®, Speedo®, Roxy®, and Grand®, respectively, in the larval homogenate of the field strain. In lab. strain, insecticides achieved the following order,: 27.11, 10.56, 26.32, 33.96 and 24.86 U/L for insecticides as described above. 5.2.5. Total protein . In field strain, protein contents were lower than the control with values: 8.23, 7. 90, 8.43, 7.17, 7.04 and 6.07 mg/g mass for Rider®, Reldane®, Biolarve®, Speedo®, Roxy®, and Grand®, respectively. Regarding lab. strain, protein contents were in the following order: 12.97, 10.70, 6.63, 10.83, 11.97, 9.53 mg/g mass for insecticides as described above. The control group did not exceed 9.83 mg/g mass.