  Complete and incomplete fusion cross sections for $^{6}$Li+$^{159}$Tb have
been measured at energies around the Coulomb barrier by the $\gamma$-ray
method. The measurements show that the complete fusion cross sections at
above-barrier energies are suppressed by $\sim$34% compared to the coupled
channels calculations. A comparison of the complete fusion cross sections at
above-barrier energies with the existing data of $^{11,10}$B+$^{159}$Tb and
$^{7}$Li+$^{159}$Tb shows that the extent of suppression is correlated with the
$\alpha$-separation energies of the projectiles. It has been argued that the Dy
isotopes produced in the reaction $^{6}$Li+$^{159}$Tb, at below-barrier
energies are primarily due to the $d$-transfer to unbound states of $^{159}$Tb,
while both transfer and incomplete fusion processes contribute at above-barrier
energies.
