Differential susceptibility to insecticides among various color morphs of the Asian citrus psyllid, Diaphorina citri

Color morphs of an insect species are known to vary in activities of detoxifying enzymes and associated susceptibility to insecticides.  In Diaphorina citri, three color morphs are known to occur.  In the present study, susceptibility to four insecticides was compared among gray/brown, blue/green and orange/yellow color morphs of field-collected D. citri.  The orange/yellow morph was significantly more susceptible to fenpropathrin than the blue/green morph, and imidacloprid and chlorpyriphos caused higher mortality in the orange/yellow morph than the blue/green and gray/brown morphs.  To confirm the genetic basis of variable levels of susceptibility, the relative expression of five CYP4 genes was compared among the color morphs.  CYP4C67 was expressed at significantly higher levels in the blue/green than in the orange/yellow and gray/brown morphs.  CYP4DA1, CYP4C68, CYP4G70, and CYP4DB1 were expressed at significantly higher levels in the blue/green and gray/brown morphs than in the orange/yellow morph.  Lower expression of CYP4 genes in the orange/yellow morph as compared with the others was correlated with reduced signal of 45 kD cytochrome P450 proteins as determined by western blot.  The results of the present study indicate differential susceptibility of D. citri color morphs to insecticides, which will need to be accounted for in future insecticide monitoring programs and may affect management programs.