الفهرس 
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Abstract
The present laboratory study aimed to investigate the toxicity and the resistance characterizations to three insect growth regulators IGR’s (teflubenzuron, methoxyfenozide and pyriproxyfen) through the selected generations of 4th instar larvae of Spodoptera littoralis (Boisd.), (Lepidoptera: Noctuidae).
The obtained results could be summarized as follows:
I. Toxicological studies
The susceptibility of the 4th instar larvae of S. littoralis to three insect growth regulators IGR’s, evaluated in the laboratory for 10 generations. The fourth instar larvae were treated with various concentrations of teflubenzuron, methoxyfenozide and pyriproxyfen for 48 h. in each generation until F10 and LC50s were calculated after 7 days post treatment in each generation.
i. The LC50 values of teflubenzuron treatment against on instar larvae through the selected generations were determined as 0.1809, 0.2275, 0.2308, 0.4123 and 0.5391ppm, in F1, F3, F6, F8 and F10, respectively, compared with 0.179 ppm in treated parent (F0). The estimated resistance ratios were ranged between 1.0106 to 3.0117 folds during 10 selected generations.
ii. Data revealed that, LC50 values of methoxyfenozide treatment against fourth instar larvae through the selected generations were determined as 0.1810, 0.1872, 0.2000, 0.2517 and 0.2830 ppm, in F1, F3, F6, F8 and F10, respectively, compared to the treated parent (F0) (LC50 = 0.1487 ppm). Resistance ratios were ranged between 1.2172 to 1.9032 folds during 10 selected generations.
iii. On the other hand the LC50 values of pyriproxyfen treatment against fourth instar larvae through the selected generations were determined as 89.349.172.224, 196.228, 309.219 and 343.472 ppm, in F1, F3, F6, F8 and F10, respectively, compared with 78.64 ppm in treated parent (F0). Resistance ratios were ranged between 1.1361 to 4.3675 folds.
The tested IGR could be arranged according to their toxicity from the most toxic compound to the lowest one as follow: teflubenzuron, methoxyfenozide then pyriproxyfen.
II. Biological Studies:
- Latent effects of teflubenzuron, methoxyfenozide and pyriproxyfen on biological aspects of 4th instar larvae of S. littoralis.
1. Effect on larvae:-
The duration of the subsequent larval instars from the initial treated one was prolonged during the following selected generations, percentage of increase in larval duration during selection with the treatment of teflubenzuron was 12.5% in the treated parent (F0), 20.1, 17.5, 35.0, 45.0 and 20.8% in survived larvae obtained in F1, F3, F6, F8 and F10 generations, respectively. In addition, during selection with methoxyfenozide was 8.0% in the treated parent (F0), 17.0, 23.0, 25.0, 40.0 and 30.0% in survived larvae obtained in F1, F3, F6, F8 and F10 generations, respectively. During selection with pyriproxyfen was 7.0% in the treated parent (F0), 22.5, 35.0, 45.0, 25.0 and 17.5% in survived larvae obtained in prementioned selected generations, respectively.
2-2- 2. Effect on pupae:-
The percentage of increase in duration of pupal stage than those of control was 3.81, 19.05, 9.52, 4.76 and 20.95% in F0, F1, F3, F6 and F10 generations respectively, while F8 had the same duration as in the control in the treatment with LC50 of teflubenzuron. On the other hand, the percentage of decrease in duration of pupal stage than those of control was obtained during selection with methoxyfenozide or pyriproxyfen treatments.
In addition, treatment of selected larvae with teflubenzuron, methoxyfenozide and pyriproxyfen caused a reduction in pupation percentage compared with control in all respective treated generations.
3. Effect on adult:
The percentages of the adult emergence were reduced significantly during the selected generations with the treatment of three insect growth regulators. The reduction percentage in adult emergence was ranged between 8.9 to 51.5%, 28.6 to 75.9% and 24.57 to 66.49% during the selected generations with LC50 of teflubenzuron, methoxyfenozide and pyriproxyfen treatments, respectively.
Adult longevity of both sexes of S. littoralis which survived from treatment of 4th instars with LC50 of teflubenzuron, methoxyfenozide and pyriproxyfen was decreased, comparing with control, during the selected generations.
The sex ratio of adult emerged from pupae developed from untreated larvae (male: female) was 0.91:1, while the selected larvae with teflubenzuron, methoxyfenozide and pyriproxyfen was in favor of female in all treated generations.
Fecundity and fertility of female moths treated as 4th instar with teflubenzuron, methoxyfenozide and pyriproxyfen was significantly reduced. Moreover, the percentages of egg hatchability decreased significantly.
Latent effects during selection with the treatment of teflubenzuron, methoxyfenozide and pyriproxyfen were extended from treated 4th instar larvae of S. littoralis to the resulted pupae and adult stages to record a morphological abnormalities reaching to 17.9 and 15.5% in the treatment of teflubenzuron, 14.17 and 19.6% in treatment of methoxyphenozide and 16.35 and 20.00% in the treatment of pyriproxyfen, respectively.
III. Biochemical studies:
a. Effect of teflubenzuron, methoxyfenozide and pyriproxyfen on specific activities of some enzymatic systems in S. littoralis.
The activity of some selected enzymatic systems was estimated after 6 days in larvae surviving the treatment of 4th instar larvae through the selected ten generations with LC50 of teflubenzuron, methoxyfenozide and pyriproxyfen.
1. Esterase activities (Non-specific esterases (*-E &*-E)):
When selection with teflubenzuron, the activities of alpha esterase (*-E) showed up and down pattern through the selected ten generations. The activity of α esterase significantly increased in F0, F3 and F6 generations. Then the activities decreased in F10 generation more than that of the control. *-esterase activity significantly decreased in the treated parent (F0) than the control, and then this activity was significantly increased in F3.
In the treatment of methoxyfenozide, the activity of a *-E was significantly reduced in treated parent (F0), F3 and F6. Meanwhile, F10 caused a non-significant decrease. *-E activity was significantly decreased in larvae of F0 and F3, then a significant increased of *-E activity in F10 was occurred.
Selection with pyriproxyfen showed a significant increase in activity of *-E during selection of generations in treated parent (F0) and F10. β-esterase activity in treated parent (F0), F3 and F6 had significantly decreased, but this activity in F10 showed a significant increase.
2. Phosphatases enzyme activities:
i- Acid phosphatase (AcP) activity:
Selection with teflubenzuron showed that the activity level of AcP reached the highest in F6 but treated parent (F0), F3 and F10 showed significant decrease. Whereas, the activity of AcP was significantly decreased in all selected generations with methoxyfenozide and pyriproxyfen.
ii- Alkaline phosphatase (AlkP) activity:
During selection with teflubenzuron, methoxyfenozide and pyriproxyfen, a high significant decrease in AlkP activity of larvae in all selected generations was found compared with the control.
3. Activity of Chitinase:
High significant increase in the treated larvae with teflubenzuron in F3, F6 and F10 generations was determined, while significant decrease was recorded in the treated parent (F0). During selection with methoxyfenozide and pyriproxyfen treatment, activity of this enzyme showed significant decrease in all tested generations comparing with control.
4. Activity of Protease:
During selection with teflubenzuron, the activity of protease enzyme in the treated parent (F0) was significantly decreased then this activity reached almost the same as normal activity (control) in F3 and F10. On the other hand, this activity showed a significantly increase in F6 than that of the control. During selection with methoxyfenozide, the activity showed a significant increase in F6. On the other hand, significant decrease was recorded in treated parent F0, F3 and F10. selection with pyriproxyfen, the activity showed significant decrease in F3 and F6. No significant change was detected in the activity of this enzyme at treated parent (F0) and F10.
b. Effect of teflubenzuron, methoxyfenozide and pyriproxyfen on some biochemical components:
1. Total proteins:
During selection with teflubenzuron, the amount of total protein was significantly decreased in treated parent (F0) and F3. On the other hand, a highly significant increase was achieved in F6 and F10 than control. Significant decrease in the total protein content of larvae during selection of generations with methoxyfenozide in treated parent (F0) and F3 was obtained. On contrary, no significant reduction was recorded in F10. In pyriproxyfen treatment, total protein was decreased in all tested generations than the control.
2. Total carbohydrates:
The effect of teflubenzuron on treated parent (F0) and F6 recorded a significant decrease in their amount of carbohydrate. In contrast, no significant reduction was recorded F3 and F10. During selection with methoxyfenozide and pyriproxyfen, total carbohydrate contents were significantly decreased in all tested generations.
3. Total lipids:
During selection with teflubenzuron, the total lipid was significantly decreased during selected generations in the treated parent F0, F3 and F6. On the other hand, a significant increase in total lipid was recorded in F10. Total lipid contents showed significant decrease during selection of generations treated with methoxyfenozide and pyriproxyfen.
c. Biochemical genetic indices:
1. α-Esterase electrophoresis patterns of S. littoralis larvae after six days of treatment as 4th instar larvae with LC50 values of teflubenzuron, methoxyfenozide and pyriproxyfen.
During selection with teflubenzuron, the total number of bands in control and selected generations (treated parent (F0), F3, F6 and F10) were 2, 2, 4, 2 and 2 respectively. There were one common band appeared in all the treated samples of generations and untreated sample (control). Two unique bands appeared only in treated parent (F0). In addition one unique band was detected in F3.
During selection with methoxyfenozide, untreated control larvae showed only two bands one of these two bands presented in the control and all selected generations. There was only one polymorphic band exhibited in all selected generations samples and not presented in untreated larvae. Each of treated parent (F0) and F6 generations had a clear unique band.
During selection with pyriproxyfen, the total number of bands were 9 bands in treated and untreated larvae. These bands distributed as 2, 2, 1, 3 and 1 in untreated, treated parent (F0), F3, F6 and F10, respectively. There was also one unique band in F6 generation.
2. β-Esterase electrophoresis patterns of S. littoralis larvae after six days of treatment as 4th instar larvae with LC50 values of teflubenzuron, methoxyfenozide or pyriproxyfen.
During selection with teflubenzuron, one polymorphic band was presented in control and all selected generations except F6. Other unique band was found in only selected generation F6.
During selection with methoxyfenozide, a total of 7 bands were characterized for the studied larvae in control and treated samples. There is two characteristic bands appeared only in F10.
During selection with pyriproxyfen, there was a characteristic band for the selected generation F3.
3. Separation of protein patterns by using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS–PAGE) technique of S. littoralis larvae after six days of treatment as 4th instar larvae with LC50 values teflubenzuron, methoxyfenozide and pyriproxyfen.
During selection with teflubenzuron, the total number of bands in control, treated parent (F0), F3, F6 and F10 were 12, 13, 11, 13 and 13 respectively. Four common bands appeared in the different samples. Three protein bands were unique in control. Neither of these three protein bands were expressed in treated larvae during selection with teflubenzuron and therefore considered as normal bands in healthy larvae. On the other hand, three protein bands appeared in treated parent (F0), F3, F6 and F10. Therefore, these bands were expressed in larvae as a response to treatment, in treated parent (F0) a characteristic band was found.
During selection with methoxyfenozide, the total number of bands in control, treated parent (F0), F3, F6 and F10 were 12, 13, 13, 11 and 13, respectively. Two bands were common bands appeared in all different samples. On contrast, two protein bands were detected only in control. These bands were not seen in the profile of treated larvae. Four protein bands were found in selected generations treated parent (F0), F3, F6 and F10. In was suggested that there bands appeared because of the treatment one unique band was detected only in each of treated parent (F0), F3 and F6.
During selection with pyriproxyfen, the total number of bands in control, treated parent (F0), F3, F6 and F10 were 12, 14, 6, 10 and 4, respectively. There was one common band presented in all samples. There were two bands considered as unique bands in untreated 6th instar larvae. Four characteristic bands in treated parent (F0) were detected. Also another one characteristic band was found in F6.