The current study was conducted to investigate the biological activities of the two strains of Bacillus thuringiensis (Bacillus thuringiensis var. Kurstaki 1(Bt K1) and Bacillus thuringiensis var. Kurstaki 2 (Bt K2)) against the newly hatched (neonate) larvae of the pink bollworm, Pectinophera gossypiella.
The two strains exhibited their toxicity against the treated larvae. Also, the lethal effect was extended in the resulted stages, pupae and adults. Based on LC₅₀ for total mortality, Bt K1 was more potent than Bt K2 where LC₅₀ was 2.21x10¹⁰ and 3.11x10¹⁰, respectively. However, the two strains were revealed a reduction of pupation and adult emergence %.  Irrespective of the strain, Bt significantly decreased larval duration and significantly increased pupal duration. No effect was recorded on morphogenesis.
In the present study,it was broadly that Bacillus thuringiensis showed its ability in the control of Pectinophora gossypiella.