Genetic analysis of chlorantraniliprole resistance in the non-target bio-control agent Trichogramma chilonis

Trichogramma chilonis (Ishii) (Hymenoptera: Trichogrammatidae), a widely used egg parasitoid of lepidopteran pests in various crops, has developed very high levels of resistance when treated with chlorantraniliprole under laboratory conditions. This study assessed and characterized its mode of inheritance, degree of dominance, realized heritability (h²), and cross-resistance. Toxicity bioassays were performed on T. chilonis adults using a dry film residue method. The chlorantraniliprole resistant strain (Chlr-R) of T. chilonis showed >25000-fold resistance as compared with chlorantraniliprole susceptible strain (Chlr-S). The chlorantraniliprole resistance in T. chilonis was characterized as incompletely dominant and governed by multiple autosomal genes. Additionally, the resistance of T. chilonis to chlorantraniliprole shifted from functionally dominant (at lower applied doses) to functionally recessive (at highest applied dose). Parameters regarding the h² of chlorantraniliprole resistance in T. chilonis predicted 10-fold rise in the initial LC₅₀ after 14.28 generations with continuous selections (at h² = 0.24). No obvious cross-resistance to cypermethrin and chlorpyrifos and a very low cross-resistance to flonicamid were detected. These findings are helpful to improve the field-based effectiveness and integration of these wasps with chemical control.