Abstract: Tebufenozide, the first commercial nonsteroidal ecdysteroid agonist, is used as a key insecticide to control the beet armyworm, Spodoptera exigua (Hübner) at present. To evaluate the risk of resistance, a field population of the beet armyworm from Shenzhen, Guangdong province was used to select for resistance to tebufenozide by dietary exposure in the laboratory. After selection with tebufenozide 62 times during 75 generations, a resistant strain was achieved with resistance ratio of 39.2 to tebufenozide compared with the original reference strain (141.3 compared with a susceptible laboratory strain). Estimation of realized heritability (h²) of resistance in different selection stages was based on the method described by Tabashnik & McGaughey. The results showed that theh₂ to tebufenozide in the early, middle and latter selection stages was 0.1075 （F₀－F₂₅）, 0.2780 （F₂₆－F₅₀） and 0.0538（F₅₁－F₇₅）, respectively. The h₂ for the entire selection experiment was 0.1556. The susceptibility to tebufenozide increased 3 times when the culture was kept for 21 generations without exposure to the chemical pressure after 43 rounds of selection. This suggested that the beet armyworm has the capability of developing resistance to tubufenozide, and it is difficult for the beet armyworm to recover the sensitivity to tebufenozide during a short period. Bioassay revealed that this resistant strain had high cross-resistance to methoxyfenozide (RR=71.4), moderate cross-resistance to abamectin (13.1), low cross-resistance to emamectin benzoate (7.0), indoxacarb (8.4) and JS118 (4.7), and a little cross-resistance to chlorfenapy (1.9). The results of resistance risk assessment suggest when tebufenozie is applied by interruption and/or alternation with other insecticides possessing a different mode of action, the resistance development rate in the beet armyworm would be delayed. However, cross-resistance between tebufenozide and other insecticides except chlorfenapy indicates that a resistance management strategy for the beet armyworm involving the rotation of these new insecticides is not likely to be effective.

Key words: Spodoptera exigua; , tebufenozide, resistance selection, realized heritability, cross-resistance