Brevicoryne brassicae

Cabbage aphids, from the genus Brevicoryne of the family Aphididae, are grayish-green, but a waxy covering gives them a grayish-white to powdery blue appearance.

Predator defense mechanism

Cabbage aphids produce a myrosinase (beta-thioglucoside glucohydrolase) enzyme in head and thoracic muscles; the aphids also uptake glucosinolates, particularly sinigrin, from the plants on which they feed, storing the glucosinolates in their haemolymph. (Glucosinolates are natural defenses for plants in the order Brassicales against pests and herbivores.) The combination of the glucosinolates and the myrosinase enzyme produces a violent chemical reaction that releases the mustard oil chemical allyl isothiocyanate. The defense mechanism has a dramatic negative effect on the survival of the larval ladybird predator Adalia bipunctata. The chemical defence of the aphids has been likened to a "walking mustard oil bomb".

The myrosinase from Brevicoryne brassicae appears to have evolved separately from myrosinases found in plants, possibly a case of convergent evolution. Aphid myrosinase appears to have greater similarity to animal beta-O-glucosidases than to plant myrosinases.