Insects can vary greatly in whole-body elemental concentrations.Recent investigations ofinsects associated with Ni hyperaecumulator plants have identified insects with relatively elevated whole.body N.leveis.Evaluation of the limited data available indicates that a whole-body Ni concentration of 500 μg Ni/g is exceptional:I propose that an insect species with a mean value of 500 μg Ni/g or greater,in either larval/nymphal or of high.Ni insects have been identified to date from studies in Mpualanga(South Africa),New Caledonia and Califoia(USA).The highest mean Ni concentration reported is 3 500μg Ni/g for nymphs of a South African Stenoscepa species(Orthoptera:Pyrgomorphidae).The majority of high-Niinsects(66%)are heteropteran herbivores.Studies of high-Ni insect host prefefence indicate they are monophagous(or nearly so)on a particular Nihyperaccuulator plant species.Much ofthe Ni in bodies of these insects is in their guts(upto 66%-75%),but elevated levels have also been found in Maipighian tubules,suggesting efficient elimination as one strategy for dealing with a high-Ni diet.Tissue levels of Ni are generally much lower than gut concentrations.butupto 1 200μg Ni/g has been reported from exuviae,suggesting that molting may be another pathway of Ni elimination.One ecological function of the high Ni concentration of these insects may be todefend them against natuml enemies.but to date only one experimental test has supported this"elemental defense"hypothesis.Community-level studies indicate that high-Ni insects mobilize Ni into food webs but that bioaccumulation of Ni does not occur at either plant-herbivore or herbivore-predator steps.Unsurprisingly,Ni bioaccumulation indices are greater for high-Ni insects compared to other insect species that feed on Ni hyperaccumulator plants.There is some evidence of Nimobilization into food webs by insect visitors to flowers of Nihyperaccumulator plants.but no high-Ni insect floral visitors have been reported.