ARS | Publication request: HOST-SWITCHING DOES NOT CIRCUMVENT THE NI-BASED DEFENCE OF THE NI HYPERACCUMULATOR STREPTANTHUS POLYGALOIDES (BRASSICACEAE)

Submitted to: South African Journal of Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 20, 2001
Publication Date: November 20, 2001
Citation: South African Journal of Science, 2001. 37:554-557

Interpretive Summary: Some plants are capable of concentrating heavy metals, such as nickel, in their tissues if they are available in the soil. One interpretation of this peculiar characteristic is that the toxic nickel defends the plant against its pests and predators. One counter-adaptation that a generalist herbivore might have to this defense would be to alternate feeding on non-toxic and then the toxic host, thereby diluting their lifetime consumption of nickel. We found that caterpillars of a feeding generalist could feed on the plants if grown in low-nickel soil, but died on the plants if grown on high-nickel soil, even is switched from a palatable species. Thus, a generalist caterpillar is unable to counter the nickel-based defense of this plant by switching hosts.

Technical Abstract: Foliar concentration of heavy metals, such as nickel, may help defend metal --hyperaccumulating plants against both herbivores and pathogens. Host switching by generalist herbivores might be one strategy by which they can dilute lifetime consumption of toxic nickel. We examined the effects of host switching on growth and survival of a generalist folivore, the beet armyworm. Early larval development on a non-toxic host was not advantageous to larvae when they were alter switched to the nickel-rich host; all ceased growth and ultimately died. Nickel-poor hosts supported their development. We conclude that polyphagous caterpillars are unable to counter Ni-based defenses via host switching.