Sublethal effects of Avermectin B1, β‐Exotoxin of Bacillus thuringiensis and Diflubenzuron against cotton leafworm (Lep., Noctuidae)

Abstract

AbstractThuringiensin (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.