A breeding scheme to isolate X chromosomes sensitive to drive by the T
8 (Trinidad) Y chromosome of Aedes aegypti (the MD haplotype) is repor
ted. Crosses with an Australian strain Th.I (Thursday Island) revealed
not only sensitive and resistant X chromosomes but also some with the
capacity to drive against the T8 Y chromosome. Four strains were crea
ted in which sex ratio was male-distorted (28-36 per cent female) for
10 generations, with no regression towards sexual parity. The proporti
on of females varied significantly between generations in each of the
four strains. Further selection produced strains with normal sex ratio
s, capable of generating fewer than 15 per cent female on outcrossing
to T8 males.