No abstract

The effect of abamectin (Avermectin B1) and thuringiensin (β‐exotoxin of Bacillus thuringiensis) on the main digestive enzymes and non‐specific esterases in Spodoptera littoralis (Boisd.) larvae was determined. The fifth‐instar larvae were allowed to feed for only 24 h on leaves treated with sublethal concentrations of each compound, i.e. 5, 20 and 200 ppm through three successive generations, respectively. In enzyme assays, at F1‐generation, abamectin (5 ppm) caused a remarkable decrease in invertase, amylase and trehalase activities by 81, 76 and 54%, respectively, compared to those recorded in the control larvae at day 3 after treatment. The body weights of larvae fed on abamectin‐treated leaves (5 ppm), generally decreased continuously during feeding periods; this decrease was directly proportional to the lower enzymatic activity. At F3‐generation, abamectin (200 ppm) reduced amylase activity by 21 and 46% at 2‐and 3‐day feeding periods, respectively. Thuringiensin, at F1‐generation (5 ppm), also caused a pronounced decrease in digestive enzyme activities, especially amylase and invertase, at which maximum inhibition, about 77 and 76%, respectively, was reached 3 days after treatment. Feeding at concentration of 200 ppm (F3‐generation) also reduced amylase and trehalase activities by 53% after 2 days of treatment. In addition, abamectin at 5 ppm caused a reduction in the activities of both α‐esterases and β‐esterases by 28.30% and 58.66%, after 1‐day feeding on leaves treated with 5 ppm (F1‐generation) and 200 ppm (F3‐generation), respectively. The inhibitory effect of thuringiensin on the enzymatic activities of both α‐esterases and β‐esterases seemed to be less than that caused by abamectin.

No abstract

The Neonicotinoid insecticides are presently used in great amounts, but this can be a problem when the possible risks of occupational and environmental contamination are considered. The objective of this study was to investigate the potential adverse effects of sublethal doses of Thiamethoxam insecticide on serum biochemical, oxidative stress and histological alterations in male albino mice via 28-day repeated-dose oral toxicity study. The possible ameliorative effect of selenium plus vitamin E against the harmful effects of Thiamethoxam was also investigated. Mice in Thiamethoxam-treated groups received three sublethal doses (6, 12, and 30 mg/kg b.w./day). Animals in another group were orally co-administered selenium + vitamin E with the higher dose of insecticide. The results showed that Thiamethoxam significantly (p < 0.05) increased cholesterol levels and liver enzyme activities, in dose-dependent manner, compared to those of the control group. Levels of creatinine were not significantly changed, whereas uric acid increased at high doses. The oxidative stress parameters were significantly increased in association with decrease in total antioxidants level. The histological analysis revealed that the higher dose induced various alterations in tissues of vital organs, i.e. liver, kidney, lung and testes. Interestingly, the ameliorative effect of selenium + vitamin E in restoring the oxidative stress parameters was reflected by reducing severity of histopathological lesions. In conclusion, it appears that the sublethal dose < 6.0 mg/kg b.w./day, in repeated dose 28-day oral toxicity study, in male albino mice may be considered as No-Observed-Adverse-Effect-Level (NOAEL) of Thiamethoxam. Additionally, the antioxidant selenium, in mixture with vitamin E, showed an ameliorative effect against Thiamethoxam-induced toxicity.

Thuringiensin (β‐exotoxin of Bacillus thuringiensis), abamectin (avermectin B1) and diflubenzuron were tested against susceptible and field strains of cotton leafworm, Spodoptera littoralis (Boisd.). Fourth‐instar larvae were fed for 3 days on leaves treated with sublethal concentrations of each compound, and surviving larvae were allowed to complete their life on untreated leaves until pupation. Larval mortality was low until 5 days after initial treatment indicating slow activity for all tested compounds. Latent effects were observed in most treatments following larval transfer to untreated leaves. The field strain appeared to be more affected in most cases by all tested compounds than the susceptible strain. All compounds, especially abamectin, resulted in a pronounced decrease of pupation in both susceptible (16–26%) and field (9.4–36.0%) strains compared with the control (78.7 and 70.8%, respectively). Also, the mean weight of pupae was significantly decreased, especially in the field strain, as a result of abamectin and thuringiensin treatments compared to that in the control. Emergence of adults in the susceptible strain was highly affected by all treatments compared to that in the control. Furthermore, fecundity of moths in the field strain was highly reduced, especially in thuringiensin (65.3–89.0%) and abamectin (57.6–87.4%) treatments compared with that of control.