INHERITANCE OF RESISTANCE TO THE BACILLUS-THURINGIENSIS CRYIC TOXIN IN SPODOPTERA-LITTORALIS (LEPIDOPTERA, NOCTUIDAE)

A strain of Spodoptera littoralis Boisduval, selected for resistance t o the Bacillus thuringiensis CryIC toxin, was used to analyze the inhe ritance of resistance. This strain resulted from a laboratory selectio n with spore-crystal preparations of B. thuringiensis CryIC toxin. At generation 12, resistance was >500 times the resistance ratio of the c ontrol. Dose-mortality curves of the resistant population, the suscept ible strain; the F-1 and the backcrosses from reciprocal crosses were compared. The resistance was partially recessive. F-1 offspring from r esistant males and susceptible females were more resistant than those from susceptible males and resistant females, indicating a clear pater nal effect. Segregation of resistance was investigated in the 8 possib le backcrosses between F-1 and one of the parental strains. Dose-morta lity responses significantly differed from those expected under the hy potheses of a major resistance gene that was either autosomal or sex l inked. It was concluded that resistance was most probably polyfactoria l. These results are discussed in relation to the nature of bacterial toxin resistance genes in various insects.