Fitness costs associated with chlorantraniliprole resistance in Spodoptera exigua (Lepidoptera: Noctuidae)

BACKGROUND The field population of Spodoptera exigua, an intermittently occurring polyphagous pest, has developed resistance to chlorantraniliprole, while whether or not such resistance carries fitness costs remains poorly understood. Here we selected six generations of the Leshan population (LS-P) by two-way selecting method, and obtained a highly resistant strain (CH-RE) and resistant degeneration strain (CH-SE) sharing a similar genetic background. After that fitness costs were evaluated by comparing the life history characteristics of CH-RE, CH-SE and the laboratory susceptible strain (SE-Lab) via the age-stage two-sex life table method. RESULTS The resistance ratio of CH-RE and CH-SE were 226.69-fold and 3.72-fold, respectively, and the estimated realized heritability (h(2)) of CH-RE was 0.058. Compared with CH-SE, the duration of pre-adult, the longevity of adult, adult preoviposition period (APOP) and average generation time (T) of CH-RE had significantly increased, but the oviposition days, average fecundity, intrinsic growth rate (r), weekly growth rate (lambda) and reproductive rate (R-0) decreased significantly. Moreover, the relative fitness of CH-RE was 0.25, and showed fitness costs. Concurrently, the fecundity of CH-SE was slightly lower than SE-Lab, but there was no significant difference in r, lambda and R-0, and the fitness (1) of CH-SE was similar to SE-Lab (1.02), which was no fitness cost. CONCLUSION These findings represent that chlorantraniliprole resistance in S. exigua has a fitness cost, and the fitness cost will disappear with the recovery of sensitivity when the insecticide is stopped for field populations, supporting that such resistance would be managed by switching off the selection pressure with rotation with alternate insecticides.