Plant interact with multiple herbivores in nature, and developed various strategies to defend against them. Using the wild cabbage populations, this thesis explores how plant interact with phloem-sucking and leaf-chewing herbivores. Infestation of aphid Brevicoryne brassicae enhanced the performance of Plutella xylostella and its parasitoid Diadegma semiclausum, but did not affect Mamestra brassicae nor its parasitoid Microplitis mediator, and the effects varied among cabbage populations. Aphid-infestation also interfered with host-foraging behavior of the parasitoids and altered plant volatile profile, but the effect depended on its duration and specific host-parasitoid interactions. However, quantification of transcription levels of maker genes related to Salicylic acid (SA) and Jasmonic acid (JA) signaling pathway showed no support for SA-JA antagonism in wild cabbages dually infested by aphids and caterpillars. In a common garden experiment, early-season aphid infestation only affected a subset of insect community associated with wild cabbage populations, the aphid and their natural enemies.