SUBLETHAL EFFECTS OF AVERMECTIN B-1, BETA-EXOTOXIN OF BACILLUS-THURINGIENSIS AND DIFLUBENZURON AGAINST COTTON LEAFWORM (LEP, NOCTUIDAE)

Thuringiensin (beta-exotoxin of Bacillus thuringiensis), abamectin (av ermectin B-1) and diflubenzuron were tested against susceptible and fi eld strains of cotton leafworm, Spodoptera littoralis (Boisd.). Fourth -instar larvae were fed for 3 days on leaves treated with sublethal co ncentrations of each compound, and surviving larvae were allowed to co mplete 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 treatm ents following larval transfer to untreated leaves. The field strain a ppeared 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 decrea sed, especially in the field strain, as a result of abamectin and thur ingiensin treatments compared to that in the control. Emergence of adu lts in the susceptible strain was highly affected by all treatments co mpared 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 contro l.