Inheritance of resistance to Bacillus thuringiensis subsp. tenebrionis CryIIIA delta-endotoxin in Colorado potato...

We investigated the genetic inheritance of Colorado potato beetle, Leptinotarsa decemlineata (Say), resistance to Bacillus thuringiensis CryIIIA delta-endotoxin. Standard reciprocal crosses and backcrosses between susceptible (S) and resistant (R) strains were used to determine the characteristics of resistance. Analysis of probit lines from the F1 reciprocal crosses indicated that B. thuringiensis delta-endotoxin resistance was inherited autosomaly without maternal effects. We estimated the degree of dominance to be 0.77 and 0.76 for the (R x S) and (S x R) F1 generations, respectively, indicating that B. thuringiensis CryIIIA delta-endotoxin resistance is conferred by incompletely dominant genes. Chi-square analysis of mortality responses of backcrossed offspring suggested that resistance might be caused by more than one locus. The stability of resistance was also studied by testing seventeen generations of resistant beetles after the selection pressure was removed. When the selection pressure was removed, the resistance level of the selected colony decreased after five generations. The resistance level did not decrease further when the selection was removed for > 12 generations.