Existence of Ramanujan primes for GL(3)

In this Note we show that given any cusp form \pi on GL(3) over the rationals, there exist an infinite number of primes p which are Ramanujan for \pi, i.e., that the local components \pi_p are tempered for an infinite number of p. It turns out that the key structural device which is needed is the degree 8 adjoint L-function of \pi.