Aptera on primary host small up to 2 mm

long), rounded, shiny (with a slight waxy bloom), varying in colour from brownish (= the late winter/early spring form) to yellowish-green; siphunculi short, pale; cauda short, tongue-like (Fig. 191b). Aptera (on secondary host) very small (often <lmm long), pale greenish or whitish-yellow to pale pinkish-white. NOTE Peach trees are colonized by Brachycaudus persicae (Passerini) (black peach aphid) and B. schwartzi (Borner) (peach aphid); these two species are distinguished from B. helichrysi by their dark siphunculi.

Brevicoryne brassicae (L.) Cabbage aphid

This notorious aphid is a widespread and generally abundant pest of brassica crops, including broccoli, Brussels sprout, cabbage, cauliflower, oilseed rape and swede. Attacked leaves may become discoloured (often reddish or purplish) and distorted, severely weakening plants and checking growth; heavily infested seedlings or young plants wilt and may die. The presence of the aphids, along with quantities of secreted wax, can also be a problem at harvest, rendering otherwise edible parts of plants useless for human consumption. The aphids may also transmit certain viral diseases, such as cabbage black ring spot, cabbage ring necrosis and cauliflower mosaic. Damaging spring populations on overwintering brassica seed crops, such as winter oilseed rape (Plate 2b), occur only following mild winters. Heavy infestations cause distortion and, often, a reddish or purplish discoloration of both leaves and pods; such damage, however, is largely cosmetic and rarely of significance.

BIOLOGY

Although commonly overwintering in the egg stage on old wild and cultivated brassica plants, wingless aphids may also survive the winter if conditions are suitably mild. Overwintered eggs hatch in April, and breeding on the original host plants is then resumed. Winged forms appear in colonies from May onwards. These spread infestations to newly planted brassica plants, where colonies develop on the underside of leaves and on flower heads. Colony development reaches its peak in the autumn, when sexual forms are produced, by which time host plants may be heavily infested and covered in aphids and secreted wax. Winter eggs are laid in the autumn, particularly during October.

DESCRIPTION

Aptera 1.6-2.6 mm long, greyish-green, with small paired black patches on the abdomen and coated with greyish-white, mealy wax; siphunculi short, barrel-shaped; cauda short, triangular

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