Larvae of spiny bollworm, Earias insulana and pink bollworm, Pectinophora gossypiella treated with Trichoderma harzianum liquid filtrate and spores of the fungus was investigated. In addition, the toxic effect of salicylic and tannic acids on the two insect species was studied. Bioassays were performed using a fungal filtrate 1, 0.5 and 0.25 ml (V/V) and spores suspension concentrations (2 × 10 5 , 1 × 10 5 and 0.5 × 10 5 spores / ml). The results showed that the mortalities of E. insulana and P. gossypiella larvae were closely related to the rates of the filtrate and the spores of T. harzianum. After infection with the fungal filtrate for 3 days, the three tested rates recorded the same mortality 60% of E. insulana. But, the mortality of P. gossypiella was 40, 33.33 and 31.67% for 1, 0.5 and 0.25 ml, respectively. On the other hand, after the same period of infection the concentrations of T. harzianum spores 2 × 10 5 , 1 × 10 5 and 0.5 × 10 5 spores / ml gave 60, 53.33 and 50% mortality and 80, 76 and 75% mortality for E. insulana and P. gossypiella, respectively. The toxic effect of salicylic acid on P. gossypiella was higher than its toxicity against E. insulana.