  For a fixed graph $H$, the $H$-IS-Deletion problem asks, given a graph $G$,
for the minimum size of a set $S \subseteq V(G)$ such that $G\setminus S$ does
not contain $H$ as an induced subgraph. Motivated by previous work about
hitting (topological) minors and subgraphs on bounded treewidth graphs, we are
interested in determining, for a fixed graph $H$, the smallest function
$f_H(t)$ such that $H$-IS-Deletion can be solved in time $f_H(t) \cdot
n^{O(1)}$ assuming the Exponential Time Hypothesis (ETH), where $t$ and $n$
denote the treewidth and the number of vertices of the input graph,
respectively.
  We show that $f_H(t) = 2^{O(t^{h-2})}$ for every graph $H$ on $h \geq 3$
vertices, and that $f_H(t) = 2^{O(t)}$ if $H$ is a clique or an independent
set. We present a number of lower bounds by generalizing a reduction of Cygan
et al. [MFCS 2014] for the subgraph version. In particular, we show that when
$H$ deviates slightly from a clique, the function $f_H(t)$ suffers a sharp
jump: if $H$ is obtained from a clique of size $h$ by removing one edge, then
$f_H(t) = 2^{\Theta(t^{h-2})}$. We also show that $f_H(t) = 2^{\Omega(t^{h})}$
when $H=K_{h,h}$, and this reduction answers an open question of Mi. Pilipczuk
[MFCS 2011] about the function $f_{C_4}(t)$ for the subgraph version.
  Motivated by Cygan et al. [MFCS 2014], we also consider the colorful variant
of the problem, where each vertex of $G$ is colored with some color from $V(H)$
and we require to hit only induced copies of $H$ with matching colors. In this
case, we determine, under the ETH, the function $f_H(t)$ for every connected
graph $H$ on $h$ vertices: if $h\leq 2$ the problem can be solved in polynomial
time; if $h\geq 3$, $f_H(t) = 2^{\Theta(t)}$ if $H$ is a clique, and $f_H(t) =
2^{\Theta(t^{h-2})}$ otherwise.
