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.

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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.

The ovicidal activity of 4 synthetic pyrethroids and 2 insect growth regulators compared with Chlorpyrifos and Methomyl were investigated by topical application against Spodoptera littoralis eggs of different ages. Synthetic pyrethroids exhibited highly pronounced ovicidal action much better than organophosphate and carbamate compounds used as standard, and Decamethrin revealed the highest activity in this respect. The chitin biosynthesis inhibitor Diflubenzuron evoked ovicidal activity higher than both of standards and its analog Trifluron (BAY SIR 8514). In all cases, as the egg‐age or/and embryonic development was considered, the more developed eggs (2–3 days old) were less sensitive than newly developed eggs (0–1 day old). Zusammenfassung Unterdrückung des Eischlüpfens bei Spodoptera littoralis mit Insektenwachstumsregulatoren und synthetischen Pyrethroiden Es wurden die oviziden Wirkungen von 4 synthetischen Pyrethroiden und 2 Insektenwachstumsregulatoren, verglichen mit den herkömmlichen Insektiziden Chlorpyrifos und Methomyl, bei Eiern von S. littoralis verschiedenen Alters unter Anwendung topikaler Applikation getestet. Die synthetischen Pyrethroide zeigten viel ausgeprägtere ovizide Wirkungen als die beiden Kontrollpräparate, wobei Decamethrin am stärksten wirkte. Der Chitinsynthese‐Hemmstoff Diflubenzu‐ron zeigte stärkere Ovizidität als die beiden Kontrollwirkstoffe und sein Analogon Trifluron (BAY SIR 8514). In allen Fällen waren die bereits weiterentwickelten Eier (2–3 Tage alt) weniger empfindlich als die frischabgelegten Eier (0–1 Tag alt).

Inhibition of reproduction in the cotton leafworm Spodoptera littoralis (Boisd.) with the antimoulting compound, Dimilin (I‐[4‐chlorophenyl]‐3 [‐2,6‐diflurobenzoyl] urea) was investigated by larval treatment. Dosage ‐ mortality response revealed 0.01 and 0.05 μg/larva to be sublethal when applied topically to the 4th instar larvae whereas 0.1 μg/larva produced absolute latent larval mortality. Exposing the 4th instar larvae to sublethal dosages of 0.05 and 0.01 μg/larva for 3 successive generations induced positive cumulative increase in larval susceptibility to the compound. Also, larval duration was prolonged significantly than untreated check. As pupation percentage was regarded, a remarkable decrease was achieved with both the succession of treated generations and increase in the sublethal dosage tested, but no effect on either pupal duration or pupal weight was observed. In addition, the lower sublethal dosage (0.01 μg/larva) induced remarkable pupal malformation percentage than the higher dosage as well as in the corrosponding emerged adults. Despite the remarkable prolongation in pre‐oviposition period adult longevity was significantly shortened. Also a highly pronounced sterilizing effect was manifested as reduction in eggs production as well as eggs viability. In general, computing the overall effect of sublethal dosages of Dimilin on reproduction performance, a suppression in cotton leafworm population of more than 99% was achieved. Zusammenfassung Uber die Reproduktionsleistung von Spodoptera littoralis (Boisd.) nach Behandlung der Larven mit subletalem Dimilin Eine topikale Behandlung der L4 von S. littoralis mit 0,01 und 0,05 μg Dimilin/Larve führte zu subletaler, mit 0,1 μg/Larve zu tödlicher Vergiftung. Wurden die L4 drei Generationen lang subletalen Dimilin‐Dosen ausgesetzt, zeigte sich eine kumulative Zunahme der Larven‐Empfindlichkeit gegenüber dem Wirkstoff. Die Larvalentwicklung wurde durch subletales Dimilin signifikant verlängert. Der Verpuppungs‐Anteil nahm im Lauf der drei Generationen bei gleicher Dimilin‐Dosis deutlich zu. Die geringere der beiden Konzentrationen bewirkte ein höheres Prozent an deformierten Puppen und Faltern als die höhere. Ungeachtet einer auffälligen Verlängerung der Präovipositionsperiode wurde die Lebensdauer der Falter nach Dimilinbehandlung der Larven signifikant verkürzt. Weiterhin wurde ein hoher Sterilisierungseffekt in Form einer Reduktion der Zahl und Lebensfähigkeit der Eier beobachtet. Insgesamt kam es unter der Einwirkung des subletalen Dimilins zu einer mehr als 99% igen Senkung der Populationsdichte.