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-Brassica crops are grown worldwide for oil, food and feed purposes, and constitute a significant economic value due to their nutritional, medicinal, bioindustrial, biocontrol and crop rotation properties. Insect pests cause enormous yield and economic losses in Brassica crop production every year, and are a threat to global agriculture. In order to overcome these insect pests, Brassica species themselves use multiple defence mechanisms, which can be constitutive, inducible, induced, direct or indirect depending upon the insect or the degree of insect attack. Firstly, we give an overview of different Brassica species with the main focus on cultivated brassicas. Secondly, we describe insect pests that attack brassicas. Thirdly, we address multiple defence mechanisms, with the main focus on phytoalexins, sulphur, glucosinolates, the glucosinolate-myrosinase system and their breakdown products. In order to develop pest control strategies, it is important to study the chemical ecology, and insect behaviour. We review studies on oviposition regulation, multitrophic interactions involving feeding and host selection behaviour of parasitoids and predators of herbivores on brassicas. Regarding oviposition and trophic interactions, we outline insect oviposition behaviour, the importance of chemical stimulation, oviposition-deterring pheromones, glucosinolates, isothiocyanates, nitriles, and phytoalexins and their importance towards pest management. Finally, we review brassicas as cover and trap crops, and as biocontrol, biofumigant and biocidal agents against insects and pathogens. Again, we emphasise glucosinolates, their breakdown products, and plant volatile compounds as key components in these processes, which have been considered beneficial in the past and hold great prospects for the future with respect to an integrated pest management.Brassicas / insect pests / chemical ecology / trophic levels / glucosinolates / isothiocyanates / defence mechanisms / biocontrol / trap crops / integrated pest management

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Many plant phytochemicals constitute binary enzyme–glucoside systems and function in plant defence. In brassicas, the enzyme myrosinase is confined to specific myrosin cells that separate the enzyme from its substrate; the glucosinolates. The myrosinase-catalysed release of toxic and bioactive compounds such as isothiocyanates, upon activation or tissue damage, has been termed ‘the mustard oil bomb’ and characterized as a ‘toxic mine’ in plant defence. The removal of myrosin cells and the enzyme that triggers the release of phytochemicals have been investigated by genetically modifying Brassica napus plants to remove myrosinase-storing idioblasts. A construct with the seed myrosin cell-specific Myr1.Bn1 promoter was used to express a ribonuclease, barnase. Transgenic plants ectopically expressing barnase were embryo lethal. Co-expressing barnase under the control of the Myr1.Bn1 promoter with the barnase inhibitor, barstar, under the control of the cauliflower mosaic virus 35S promoter enabled a selective and controlled death of myrosin cells without affecting plant viability. Ablation of myrosin cells was confirmed with light and electron microscopy, with immunohistological analysis and immunogold-electron microscopy analysis showing empty holes where myrosin cells normally are localized. Further evidence for a successful myrosin cell ablation comes from immunoblots showing absence of myrosinase and negligible myrosinase activity, and autolysis experiments showing negligible production of glucosinolate hydrolysis products. The plants where the myrosin defence cells have been ablated and named ‘MINELESS plants’. The epithiospecifier protein profile and glucosinolate levels were changed in MINELESS plants, pointing to localization of myrosinases and a 35 kDa epithiospecifier protein in myrosin cells and a reduced turnover of glucosinolates in MINELESS plants.