The A58T and R79E mutations in BTβ1 of a neonicotinoid resistant B . tabaci MEAM1 strain.

( A ) Resistance levels of the B . tabaci strains to seven neonicotinoid insecticides. IMI, imidacloprid; THX, thiamethoxam; CLO, clothianidin; ACE, acetamiprid; DIN, dinotefuran; NIT, nitenpyram; THIA, thiacloprid. Values were generated by calculating the LC 50 value of each strain to each insecticide and comparing to those of the S #1 strain. Different letters on heat map represent significant difference between their LC 50 values for each insecticide ( P < 0.05). ( B ) Mortalities of mutant B . tabaci strain in synergism bioassays. Values are means of three biological replicates ( n = 3). Whiteflies fed insecticide without synergist were used as control. ( C ) Location of the A58T and R79E mutations in BTβ1 . Loop G region in exon 2 and Loop D region in exon 3 are indicated by the black line above. ( D ) Frequency of A58T&R79E in neonicotinoid susceptible and resistant strains. S #1 and S #2 are two laboratory neonicotinoid susceptible strains, R #1 is a neonicotinoid resistant field strain, and R #2 was a homozygous mutant strain derived from R #1 . Sixty individuals of each strain were genotyped. ( E ) Nonlinear response curve of the mortality of B . tabaci strains against log-doses of different neonicotinoids. Values are mean ± SEM ( n = 3). Different letters on LC 50 values represent significant difference ( P < 0.05). ( F ) Relative expression levels of BTβ1 after feeding adult whiteflies dsBTβ1. Adult whiteflies fed on dsEGFP were used as control. Values are means of three biological replicates ( n = 3), asterisks represent significant difference between the treatments and controls (*** P < 0.001). ( G ) Difference in mortality of B . tabaci strains fed dsEGFP or dsBTβ1 and exposed to different insecticides. Values are means of three biological replicates ( n = 3). Circles of different size represent significant difference (ns, no significant difference; *, P < 0.05; **, P < 0.01).