Egg-mimics of Streptanthus (Cruciferae) deter oviposition by Pieris sisymbrii (Lepidoptera: Pieridae).

Streptanthus breweri, a serpentine-soil annual mustard, produces pigmented callosities on its upper leaves which are thought to mimic the eggs of the Pierid butterfly Pieris sisymbrii. P. sisymbrii is one of several inflorescence-infructescence-feeding Pierids which assess egg load visually on individual host plants prior to ovipositing. Removal of the "egg-mimics" from S. breweri plants in situ significantly increases the probability of an oviposition relative to similar, intact plants.