Hypersensitivity reaction of Brassica nigra L. (Cruciferae) kills eggs of Pieris butterflies (Lepidoptera: Pieridae).

Some individual plants of the mustard Brassica nigra in lowland California kill eggs of the Crucifer-specialist herbivores Pieris rapae and P. napi by producing a necrotic zone at the base of the egg, thereby apparently desicating it. This is a typical hypersensitivity reaction, but to an atypical stimulus. The eggs can be "rescued" by maintaining them in a saturated atmosphere. Attempts to demonstrate a bacterial or fungal agent associated with the reaction were unsuccessful.