Larval tolerance in the Drosophila melanogaster species complex toward the two toxic acids of the D. sechellia host plant.

The toxicity of hexanoic (C6) and octanoic (C8) acids, the two major components of the host plant of Drosophila sechellia, was investigated upon larvae of the four species included in the D. melanogaster complex and on interspecific hybrids between D. sechellia and D. simulans. Specific methods had to be devised for obtaining reproducible toxicity results. The three generalist species (D. melanogaster, D. mauritiana and D. simulans) were found to be very sensitive, as indicated by low lethal concentrations and an increase in development duration. By contrast D. sechellia was much more tolerant, especially toward C8 which is the most abundant product in the natural resource. Interspecific hybrids (F1 and backcrosses) exhibited intermediate characteristic, but a dominance of D. simulans sensitivity was observed for both acids and especially for C8. Data on larvae are quite different from those previously obtained on adults, and are more likely to reflect the natural selective pressures existing in the wild.