Boivin, G., Hance, T. and Brodeur, J. 2012. Aphid parasitoids in biological control. Can. J. Plant Sci. 92: 1-12. Aphids are important pests of most cultivated crops worldwide. Among the natural enemies that regulate their populations, aphid parasitoids are commonly used in biological control programs in greenhouses and field situations. They belong to the Hymenoptera (Braconidae and Aphelinidae), and a few species are Diptera (Cecidomyiidae). Aphid parasitoids are themselves exposed to a variety of natural enemies including predators, fungi and hyperparasitoids. The most important impediment to the use of aphid parasitoids as biological control agents remains the production cost to mass-rear parasitoids. Rearing either aphids or directly aphid parasitoids in artificial media could be a solution to produce large quantities of aphid parasitoids at low cost, but such an approach still faces numerous challenges related to the nutritional and physiological requirements of developing aphid parasitoids.