INHERITANCE AND STABILITY OF RESISTANCE TO BACILLUS-THURINGIENSIS FORMULATIONS OF THE DIAMONDBACK MOTH, PLUTELLA-XYLOSTELLA (LINNAEUS) (LEPIDOPTERA, YPONOMEUTIDAE)

Levels, genetic traits and stability of resistance to Bacillus thuringiensis (BT) of the Kohno populations (RO and ROO) of the diamondback moth Plutella xylostella were investigated by the leaf-dip method. The RO and ROO populations exhibited 78.5 and 704-fold resistance to BT (Toarow CT(R)), respectively, high levels of resistance to other formulations derived from B.t. subsp. kurstaki, and low resistance to BT derived from subsps. kurstaki and aizawai. Analysis of dosage-mortality relationships of F1, F2 and backcross progenies derived from the cross of susceptible (S) and ROO populations revealed that BT resistance was primarily controlled by an incompletely recessive, autosomal single allele. High levels of BT resistance in the moth have decreased within generations in the absence of insecticidal selection. The RO population exhibited 46- and 52-fold resistance to the tertiary amines, cartap and thiocyclam, respectively. Resistance to tertiary amines have remained at high levels without insecticidal selection.