Abstract: The lambda-cyhalothrin resistant males and susceptible females in Spodoptera exigua were crossed in the laboratory. The 4th-instar larvae derived from the F₂ inbred progeny were treated with the dose of 50 μg/mL of lambda-cyhalothrin, and survivors were taken into the second selection at the dose of 250 μg/mL in the following day. The survival adults (♂) after the second selection were backcrossed with the susceptible adults (♀)，and their inbred progeny was selected with a similar method until the near isogenic line (NIL) strain resistant to lambda-cyhalothrin were established after the process was repeated 6 times. During the establishment process of the NIL strain, the resistance level and biological parameters in every generation were assayed. The results indicated that resistance level to lambda-cyhalothrin of NIL-RR (resistant strain) had no significant decrease compared to the parent resistant strain. Esterase analysis to the 4thinstar larvae of the susceptible, resistant and NIL-RR strains showed that the pattern of esterase band of NIL-RR was similar to that of parent susceptible strain, but significantly different with the parent resistant.

Key words: Spodoptera exigua, lambdacyhalothrin, near isogenic line