Potent natural egg-laying stimulant for cabbage butterflyPieris rapae.

Solutions of glucobrassicin (3-indolylmethyl glucosinolate) purified from foliage and sinigrin (allyl glucosinolate) elicited oviposition by the cabbage butterfly,Pieris rapae, at threshold concentrations as low as 10(-6) M. At higher concentrations, glucobrassicin elicited a faster oviposition rate and a stronger visual response to the substrate through associative learning. Solutions of 10(-5) M glucobrassicin and 10(-2) M sinigrin stimulated equally. Their enzymic hydrolysis products failed to influence oviposition. The markedly greater potency of glucobrassicin is consistent with known glucosinolate profiles of crucifers which show indolyl glucosinolates predominant in foliage.