Host plant selection of Chrysolina clathrata (Coleoptera: Chrysomelidae) from Mpumalanga, South Africa
Hyperaccumulated elements such as Ni may defend plants against some natural enemies whereas other enemies may circumvent this defense. The Ni hyperaccumulator Berkheya coddii Roessler (Asteraceae) is a host plant species for Chrysolina clathrata (Clark), which suffers no apparent harm by consuming its leaf tissue. Beetle specimens collected from B. coddii had a whole body Ni concentration of 260 mu g/g dry weight, despite consuming leaf material containing 15 100 mu g Ni/g. Two experiments were conducted with adults of this beetle species: a no-choice experiment and a choice experiment. In the no-choice experiment we offered beetles foliage of one of four species of Berkheya: B. coddii, B. rehmannii Thell. var. rogersiana Thell., B. echinacea (Harv.) O. Hoffm. ex Burtt Davey, and B. insignis (Harv.) Thell. The two former species are Ni hyperaccumulators (defined as having leaf Ni concentration > 1 000 mu g/g) whereas the latter have low Ni levels (< 200 mu g/g) in their leaves. Masses of beetles were monitored for 6 days. Choice experiments used growing stem tips from the same Berkheya species, placed into Petri dishes with five Chrysolina beetles in each, and the amount of feeding damage caused on each of the four species was recorded. Beetles in the no-choice experiment gained mass when offered B. coddii, maintained mass on leaves of the other Ni hyperaccumulator (B. rehmannii var. rogersiana), and lost mass when offered non-hyperaccumulator leaves. In the choice test, beetles strongly preferred B. coddii to other Berkheya species. We conclude that C. clathrata may be host-specific on B. coddii.