Genetic Analysis of Deltamethrin Resistance in Laboratory-Selected Strains of Drosophila melanogaster MEIG

The genetic basis of deltamethrin resistance or sensitivity in two strains of Drosophila melanogaster was studied by means of chromosomal analysis. Eight homozygote combinations of resistant (SR) and sensitive (HS1) strains were constructed by chromosome substitution and were tested using topical bioassay and electrophysiological tests. The analysis of the data showed that resistance to lethal effects was multigenic, with the major factor(s) located on the first (X) and second chromosomes. One significant positive interaction between the two chromosomes was also found. For the resistance to knockdown (measured by time-based topical test), the second chromosome was found to be much more important than the first and third chromosomes. However, analysis of the onset of the deltamethrin-induced electrical activity for each constructed strain suggested that reduced nerve sensitivity (probably associated to the deltamethrin resistance) was linked to both chromosomes X and 2. Similarly, bursts of large excitatory junctional currents (which were observed in sensitive and wild strains following topical application of deltamethrin) were not observed in resistant strains when these two chromosomes originated from the SR strain. A good correlation was found between the latency and LD50 suggesting that the same factors might be involved in the electrophysiological effects and the lethal effects. In our strains, resistance most probably corresponds to reduced nerve sensitivity. Our data are consistent with the location of the sodium channel gene in Drosophila on the chromosome X but clearly demonstrate that this major gene cannot by itself explain target site resistance to deltamethrin.