Essential support of Green biset functors via morphisms

We present a very natural but yet useful criterion to detect vanishing of essential algebras of a Green biset functor $A$ by means of morphisms. We introduce the morphisms $Inf:A\to A_G$ and $Res:A_G\to A$ to prove that the class of groups for which the essential algebras do not vanish is the same for $A$ and any shifted functor $A_G$. We use the kernel of $Res$ to give a characterization of the seeds of simple $A_G$-modules which are not obtained as pullback of simple $A$-modules.