ß-aminobutyric acid (BABA) is a non-protein amino acid that primes plant defences against a range of micropathogens. We have recently demonstrated that application of BABA to plant roots can also inhibit sap-feeding insects such as aphids. Using a model system involving beans (Vicia faba), pea aphids (Acyrthosiphon pisum) and the hymenopterous aphid parasitoid Aphidius ervi we are currently examining the consequences of this chemically-induced herbivore suppression on the performance of higher trophic levels. Female parasitoids show no avoidance of aphids reared on BABA treated plants and choice-tests using Y-tube olfactometers indicate that BABA does not deter females from responding positively to volatiles released from aphid-infested beans. However, parasitized aphids developing on BABA-treated plants have reduced A. ervi emergence rate and produce smaller wasps. Whether this BABA-induced inhibition of A. ervi is caused by decreased host size, plant-sourced xenobiotics or direct suppression by BABA present in the aphid is being investigated.