The elevated Ni concentration of Ni hyperaccumulator plants has been proposed to be an effective chemical defence against herbivores. To test this hypothesis, we fed leaves from hyperaccumulator and non-hyperaccumulator populations of South African Senecio coronatus to a generalist herbivore species, the brown garden snail (Helix aspersa). Snails fed hyperaccumulator leaves experienced significantly greater mortality than those fed non-hyperaccumulator leaves and also contained 10-fold greater concentrations of Ni. A choice experiment showed snails preferred non-hyperaccumulator leaves in two of three trials. Snails fed cornmeal diet amended with Ni had significantly reduced mass for diets containing as little as 140 mg Ni g − 1 , and significantly greater mortality occurred for snails consuming diets containing 830 mg Ni g − 1 and greater. Because hyperaccumulator S. coronatus leaves contained far more Ni (12,100 mg Ni g − 1 ) than the toxic threshold shown in the diet experiment, we concluded that the Ni concentration of hyperaccumulator leaves was sufficient to cause the elevated mortality of snails fed those leaves. This research adds another example to the growing literature showing the toxicity of hyperaccumulated Ni to generalist folivores.

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Arthropods (mainly insects) were collected from a forest site that contained at least six species of Ni hyperaccumulators. Whole body Ni analysis was performed for 12 arthropod taxa, two of which were studied at different life cycle stages. We found two Nitolerant insects. The pentatomid heteropteran Utana viridipuncta, feeding on fruits of the Ni hyperaccumulator Hybanthus austrocaledonicus, contained a mean of 2 600 µg Ni/g in nymphs and 750 µg Ni/g in adults. The tephritid fly Bactrocera psidii, feeding on pulp of Sebertia acuminata fruits that contained 6 900 µg Ni/g, contained 420 µg Ni/g as larvae that had evacuated their guts and significantly less (65 µg Ni/g) as adults. European honeybees (Apis mellifera) visiting flowers of the Ni hyperaccumulator H. austrocaledonicus contained significantly more Ni (8-fold more) than those collected from flowers of Myodocarpus fraxinifolius, a non-hyperaccumulator. Our results show that some insects feed on Ni hyperaccumulator plants and that their feeding mobilizes Ni into local food webs.

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