Brevicoryne brassicae (cabbage aphid).

Crops which can suffer severe attack by B. brassicae include cabbage, cauliflower, broccoli, radish, swede and mustard. Kale, oilseed rape and Brussels sprouts are usually only lightly infested, while turnips appear immune. Large colonies feed on the undersides of young leaves, draining plant nutritional resources, and on the flower heads of seed crops, reducing the setting of seed (Blackman and Eastop, 2000). On cabbage in Germany, numbers of aphids on the plants peaked in June-July and again in September-October. The yield was most affected by attack in the second population peak. Control thresholds for fresh consumption were 20% plants attacked with more than 10 apterae/plant, or 10% attacked plants when one or more plants had more than 100 aphids (Hildenhagen and Hommes, 1997).B. brassicae was very numerous on yellow mustard (Sinapis alba) in a study in Poland, in which early infestations (at the bud development stage) prevented stalk development and caused premature plant death; while later infestations (at the peak or end of blooming) caused high yield reductions (Hurej and Preiss, 1997). Among several aphids infesting brassica crops, B. brassicae was generally the most prevalent during the growing season (e.g. Trumble, 1982; Raworth, 1984; Nematollahi et al., 2014a). It occurred primarily on the highest and youngest leaves and stems, with the highest aphid density recorded at the head formation stage on broccoli and the stem elongation stage on oilseed rape (Trumble, 1982; Nematollahi et al., 2014a). B. brassicae significantly preferred the upper parts (upper 10-15 cm of the stem) of oilseed rape plants to the lower parts (the rest of the stem) (Nematollahi et al., 2014a).B. brassicae can sometimes reduce both crop yield and quality of spring and winter oilseed rape in Europe. In field experiments in the UK, yield responses to insecticide treatment tended to be larger in spring-sown than in winter-sown oilseed rape, mainly because it became more heavily infested at an early growth stage. B. brassicae is a sporadic oilseed rape pest, however, that will only rarely reach threshold numbers for control (Ellis et al., 1999). Daebeler and Hinz (1980) presented an analysis of yield loss in winter rape in Germany. They showed that by the time crops become heavily infested, serious injury will already have occurred, so control measures need to be taken early. Experimental studies showed that B. brassicae could reduce fresh and dry weight, leaf area and concentration of amino acid in aphid-infested plants (van Emden, 1990). B. brassicae hampers photosynthesis in a range of oilseed brassicas (Arjad Hussain et al., 2014; Razaq et al., 2014). In regions with warm climates, parthenogenetic reproduction can occur throughout the year. Considerable damage can occur to vegetables, particularly those grown for seed. In the Middle East, alatae migrate to cruciferous vegetable crops in autumn-early winter, migrating to wild Cruciferae in spring where they pass the summer. In Nigeria, cabbages with high uncontrolled infestations usually suffer stunted growth, plant death and low yields (Parh et al., 1987). In Himachal Pradesh, India, the avoidable yield losses caused by an aphid complex (B. brassicae, Lipaphis erysimi and Myzus persicae) to three different cruciferous oilseed crops, Brassica campestris var. toria, B. campestris var. sarson and B. juncea, were 67.61, 62.51 and 50.00%, respectively. Most of the losses occurred when the infestation was prevalent during the flowering stage. These losses were checked by insecticide applications at the initiation of flowering (Sharma and Kashyap, 1998). Late-season insect infestation of Brassica napus, B. rapa, B. juncea and Sinapis alba was studied in Idaho, USA. Aphid colonization (primarily B. brassicae) was observed on all these plant species, but infestation on S. alba and B. rapa occurred too late to have a major effect on seed yield. Seed oil content of rape species was significantly reduced by insect damage (B. brassicae, along with Ceutorhynchus assimilis and Plutella xylostella), although oil quality (indicated by fatty acid profile) was not affected. Uncontrolled insect infestation reduced seed yield of rape species by 37 and 32% in B. napus and B. rapa, respectively (Brown et al., 1999). B. brassicae is a vector of about 20 plant viruses, including Turnip mosaic virus (as cabbage black ringspot, cabbage ring necrosis and radish mosaic) and Cauliflower mosaic virus (Blackman and Eastop, 2000).