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 × 10⁵, 1 × 10⁵ and 0.5 × 10⁵ 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 × 10⁵, 1 × 10⁵ and 0.5 × 10⁵ 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. After 13 days of treatment, it was exhibited 50, 48, 46, 45 and 45% mortality of E. insulana and 86.67, 83, 80, 78 and 76.67% mortality of P. gossypiella at the concentrations 1900, 1425, 950, 475 and 237.5 ppm, respectively. Tannic acid gave 70, 65, 63, 62 and 62% mortality for E. insulana and 45, 42, 40, 36.66 and 31.66% for P. gossypiella at the tested concentrations 2000, 1500, 1000, 500 and 250 ppm, respectively.