Alyssum corsicum and Alyssum murale can accumulate extraordinary concentrations of Ni (10,000- 20,000 ppm) from soil , which may provide “elemental defense” against herbivores that are resistant to their chemical arsenal of glucosinolates. We used Alyssum plants grown in soil with and without Ni to investigate feeding behavior, reproduction and survival of harlequin cabbage bug (Murgantia histrionica), a specialist feeder on plants in the Brassicaceae. Field collections of Murgantia from Alexandria and Staunton, VA were maintained on cabbage in mesh cages to provide eggs and adults for these studies. Nymph feeding, development and survival were evaluated through daily observations of first- instar nymphs in a “no choice” design with 5 food treatments (1 new leaf daily): A. corsicum with and without Ni , A. murale with and without Ni and Brassica juncea (Indian mustard) without Ni. Adult feeding, reproduction and survival were evaluated by caging 4 Murgantia (2 of each gender) in a “no choice” design with 1 intact plant (3 food treatments): A. corsicum with and without Ni, and B. juncea without Ni. Herbivory damage to Alyssum plants was evaluated by placing 4 adult Murgantia in a “choice” design with 2 plants of each species with and without Ni.
Results/Conclusions
Image analysis of leaf area consumed showed that nymphs ate significantly more Brassica compared to Alyssum, and they showed a trend for less consumption of Alyssum leaves with Ni. Nymphs eating Alyssum with Ni suffered very high mortality (94-100%), compared to nymphs eating Alyssum without Ni (13%). Nymphs eating Alyssum took significantly longer to molt compared to nymphs ingesting Brassica. Adults in the “no choice” treatment also showed high mortality (41%) on Alyssum plants with Ni compared to mortality on Alyssum without Ni (27%) and Brassica (6%). Adults on Alyssum plants with and without Ni were observed feeding with equal frequency, but insects on Brassica fed significantly more often. Adults on Alyssum plants with and without Ni laid an equal number of eggs, but insects on Brassica laid significantly more eggs. In the “choice” studies with Murgantia, no difference was seen in shoot biomass after herbivory for A. murale plants with and without Ni. In A. corsicum however, plants grown in soil with Ni had significantly greater shoot biomass after herbivory compared to plants grown in soil without Ni.