Cross-resistance among common insecticides and its possible mechanism in <i>Laodelphax striatellus</i> Fallén (Hemiptera: Delphacidae)

<p><i>Laodelphax striatellus</i> Fallén, is a serious pest of rice, has developed resistance to various chemical insecticides. Thus, clear documentation of resistance and cross-resistance is required for good resistance management. This study examined cross-resistance among common insecticides acting on different targets and its mechanism. First, the <i>L. striatellus</i> strains selected with chlorpyrifos, deltamethrin and imidacloprid were tested for cross-resistance to common insecticides. Then, these three resistant strains underwent mixed breeding for two generations, as an original population and reselected for seven generations by corresponding insecticides, resulting in three new resistant strains. These strains were tested for confirmation of the cross-resistance and the mechanism was analysed by comparing the expression levels of related detoxification enzyme genes. The results demonstrated that cross-resistance existed among chlorpyrifos, deltamethrin and imidacloprid. The detoxification enzyme gene <i>CYP6AY3v2</i>, <i>CYP306A2v2</i> and <i>CYP353D1v2</i> were found to be up-regulated in the chlorpyrifos-selected strain; <i>CYP6AY3v2</i>, <i>CYP6FU1</i>, <i>CYP353D1v2</i>, and <i>CYP439A1v3</i> in the Deltamethrin-selected strain; and <i>CYP4C72</i>, <i>CYP6AY3v2</i> and <i>CYP353D1v2</i> in the Imidacloprid-selected strain. Furthermore, overexpression of <i>CYP6AY3v2</i> and <i>CYP353D1v2</i> was in concert with cross-resistance in selected strains. These results suggest that <i>CYP6AY3v2</i> and <i>CYP353D1v2</i> might be associated with the cross-resistance among chlorpyrifos, deltamethrin and imidacloprid in <i>L. striatellus</i>.</p>