In general newts eat other food on land than in water. My pleuro's don't eat frozen mosquito larves on land, but live food like worms only.
On the other hand, I keep my pleuro's only on land if they need to be for health reasons, it happened only once for one newt.
I recommend keeping your pleuro's in water entirely. I experimented with landarea's as well and mine prefer to be in the water or only a bit out, not fully.