  Applying perturbation theory methods, the absence of the point spectrum for
some nonselfadjoint integro-differential operators is investigated. The
considered differential operators are of arbitrary order and act in either
$\mathbf{L}_{p}(\mathbb{R}_{+})$ or $\mathbf{L}_{p}(\mathbb{R}) (1\leq
p<\infty)$. As an application of general results, new spectral properties of
the perturbed Hill operator are derived.
