Abstract: The cross-resistances to 13 insecticides in different resistant NILs-RR and NILs-RS strains of Spodoptera exigua to Lambda-cyhalothrin were determined in the laboratory. The results indicated that the high resistance strain (NILs-RR) showed a high level to all of the tested pyrethroids (15.2- to 92.6- fold), middle level to fipronil, abamectin, methomyl, and methylaminoavermectin (14.1- to 67.5-fold), and low level to chlorpyrifos, chlorfenapyr, tebufenozide and phoxim(3.0- to 7.2-fold). However, it was found that the low resistance strain (NILs-RS) possessed much high level to fipronil and abamectin (13.3- to 14.3-fold), moderate level to α-cypermethrin, fenvalerate, methomyl, chlorfenapyr and methylaminoavermectin (5.8- to 9.9-fold), and low level to beta-cyfluthrin, deltamethrin and fenpropathrin (2.6- to 2.9-fold). Relative fitness experiments for the populations of lambda-cyhalothrin-susceptible (SS), NILs-RR and NILs-RS strains of Spodoptera exigua, showed that relative finesses of NILs-RS and NILs-RR were 0.870 and 0.893, in comparison with that of SS strain. The intrinsic rates of natural increase of SS, NILs-RR and NILs-RS were 624.7, 543.6, and 557.8 respectively. There was no significant difference in the fitness between SS and different resistant lambda-cyhalothrin genotypes (NILs-RS and NILs-RR) of Spodoptera exigua. From the research, other pyrethroids, fipronil and abamectin are the high cross-resistance level insecticides to the lambda-cyhalothrin resistance of Spodoptera exigua, and couldn't be mixtured and rotated; But phoxim, tebufenozide and chlorpyrifos could be used with lambda-cyhalothrin for the lower cross-resistance risk. In the high lambda-cyhalothrin resistance level area, immigrated into the susceptible population maybe a good approach for resistance management.

Key words: Spodoptera exigua, Lambda-cyhalothrin, Cross-resistance, Fitness