The tannakian formalism and the langlands conjectures

Let H be a connected reductive group over an algebraically closed field of characteristic zero, and let 0 be an abstract group. In this note, we show that every homomorphism of Grothendieck semirings φ: K+0[H]→K0+[Γ], which maps irreducible representations to irreducible, comes from a group homomorphism ρ:Γ→H(K). We also connect this result with the Langlands conjectures.