Fusion-invariant representations for symmetric groups

For a prime $p$, we show that uniqueness of factorization into irreducible $\Sigma_{p^2}$-invariant representations of $\mathbb{Z}/p \wr \mathbb{Z}/p$ holds if and only if $p=2$. We also show nonuniqueness of factorization for $\Sigma_8$-invariant representations of $D_8 \wr \mathbb{Z}/2$. The representation ring of $\Sigma_{p^2}$-invariant representations of $\mathbb{Z}/p \wr \mathbb{Z}/p$ is determined completely when $p$ equals two or three.
Comment: 27 pages. Comments are welcome