NICKEL HYPERACCUMULATED BY THLASPI-MONTANUM VAR MONTANUM IS ACUTELY TOXIC TO AN INSECT HERBIVORE

Some plants growing on serpentine soils sequester (hyperaccumulate) nickel from those soils in their tissues. Several ecological functions for metal hyperaccumulation have been suggested, including defense against herbivores. This study tests the herbivore defense hypothesis using the Ni hyperaccumulator Thlaspi montanum var. montanum. Leaves differing 167-fold in Ni content (3,000 vs 18 ppm) were obtained by growing plants on high- and low-Ni soils. Leaves were fed to larvae of Pieris rapae, a generalist folivore. Larvae fed high-Ni leaves did not grow and suffered 100% mortality after 12 d, whereas those fed low-Ni leaves quadrupled in weight with a corresponding mortality of only 21%. Larvae fed an artificial diet containing 0, 100, 500, or 1,000 ppm Ni showed acute toxicity at 1,000 ppm. We conclude that hyperaccumulated Ni can poison folivores that feed exclusively upon Ni-hyperaccumulating species and therefore is an herbivore defense for some plants native to serpentine soils.