USE OF RECOMBINANT INBRED LINES FOR THE INVESTIGATION OF INSECTICIDE RESISTANCE AND CROSS-RESISTANCE IN DROSOPHILA-SIMULANS

Despite the sequent occurrence and economic importance of pesticide re sistance in insects, it has not always been possible to clearly identi fy and characterize its genetic basis. Three questions, the number of genes responsible for resistance, the degree to which resistance to mu ltiple classes of compounds is the result of common mechanisms, and th e identity of resistance genes, are ones that have sometimes proven re fractory to definitive analysis. To address these questions, we create d two sets of recombinant inbred lines of Drosophila simulans, crossin g strains resistant to malathion, carbaryl, and permanone with a strai n sensitive to those compounds, followed by 15 generations of single-p air mating. Forty-four lines were obtained, each one of which should b e homozygous for differing portions of the resistant and sensitive pro genitor genomes. We then measured resistance to each pesticide in each line and determined its genotype for five candidate resistance locis by means of PCR-based scoring of sequence differences. From these anal yses, the following points emerged: (1) Resistance to malathion and pe rmanone is due to the actions of multiple genes, while resistance to c arbamate is largely determined by a single major gene. (2) Correlation s between resistance to the different pesticides suggests that, at lea st to an extent, common mechanisms are involved in determining resista nce to all three. (3) A polymorphism in the Ace locus, encoding acetyl cholinesterase, the target site of malathion and carbaryl action, cose gregates with malathion resistance and is correlated with carbaryl res istance. The resistant allele encodes a protein with at least one amin o acid difference with the sensitive one, a leu --> met substitution a t position 299, near the active site of the protein. The protein from the resistant line has an eightfold lower affinity for malaoxon than d oes the protein from sensitive flies; no such difference was observed with respect to carbaryl. (4) The distribution of alleles in the recom binant inbred lines of other candidate loci examined-mdr50, pam, dsc, and GSTD1-indicate that they do not contribute to resistance to any of the three pesticides. Taken together, we feel that our results demons trate that use of recombinant inbred lines may be a powerful new tool for the analysis of insecticide resistance, particularly in those spec ies where laboratory culture is feasible and genetic map information i s available. (C) 1998 Academic Press.