INHERITANCE OF RESISTANCE TO BACILLUS-THURINGIENSIS SUBSP TENEBRIONISCRYIIIA DELTA-ENDOTOXIN IN COLORADO POTATO BEETLE (COLEOPTERA, CHRYSOMELIDAE)

We investigated the genetic inheritance of Colorado potato beetle, Lep tinotarsa decemlineata (Say), resistance to Bacillus thuringiensis Cry IIIA delta-endotoxin. Standard reciprocal crosses and backcrosses betw een susceptible (S) and resistant (R) strains were used to determine t he characteristics of resistance. Analysis of probit lines from the F- 1 reciprocal crosses indicated that B. thuringiensis delta-endotoxin r esistance was inherited autosomaly without maternal effects. We estima ted the degree of dominance to be 0.77 and 0.76 for the (R x S) and (S x R) F-1 generations, respectively, indicating that B. thuringiensis CryIIIA delta-endotoxin resistance is conferred by incompletely domina nt genes. Chi-square analysis of mortality responses of backcrossed of fspring suggested that resistance might be caused by more than one loc us. The stability of resistance was also studied by testing seventeen generations of resistant beetles after the selection pressure was remo ved. When the selection pressure was removed, the resistance level of the selected colony decreased after five generations. The resistance l ever did not decrease further when the selection was removed for >12 g enerations.