Accumulation of glucosinolates by the cabbage aphid Brevicoryne brassicae as a defense against two coccinellid species.

Brassica nigra plants, characterized by high levels of sinigrin, and artificial aphid diets to which sinigrin was selectively added were used to rear the crucifer specialist, Brevicoryne brassicae. Aphids were provided as a food source to two species of polyphagous ladybird, Adalia bipunctata and Coccinella septempunctata. First instar A. bipunctata were unable to survive when fed with B. brassicae reared on B. nigra or diets containing 0.2% sinigrin, but when fed with aphids reared on diets containing 0% sinigrin, survival rates were high. By contrast, first instar C. septempunctata were able to survive when fed with aphids reared on B. nigra or artificial diets containing up to 1% sinigrin. However, the presence of sinigrin in the aphid diet decreased larval growth and increased the time necessary for larvae to reach second instar for this species of ladybird. These results indicate that the presence of sinigrin in the diet of B. brassicae makes this aphid unsuitable as a food source for A. bipunctata but not for C. septempunctata, although for this ladybird species, there appear to be costs associated with feeding on aphids that contain this secondary metabolite.