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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Research Unit » Research » Publications at this Location » Publication #219895
Title: Can a Pathogen Provide Insurance against Host Shifts by a Biological Control Organism?

Author
item MCEVOY, PETER - OREGON STATE UNIVERSITY
item KARACETIN, EVRIM - OREGON STATE UNIVERSITY
item Bruck, Denny

Submitted to: International Symposium on Biological Control of Weeds
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2007
Publication Date: 6/23/2008
Citation: Mcevoy, P.B., Karacetin, E., Bruck, D.J. Can a Pathogen Provide Insurance against Host Shifts by a Biological Control Organism? In Julien, M.H., Sforza, R., Bon, M.C. Evans, H.C., Hatcher, P.E., Hinz, H.L., Rector, B.G. editors. Proceedings of the XII International Symposium on Biological Control of Weeds. Oxfordshire. CAB International. p. 37-42.

Interpretive Summary: The cinnabar moth is an icon in population ecology and biological control that has recently lost its shine based on evidence that (1) it is less effective than other biological alternatives (2) it eats (harms) non-target plant species and potentially harms the animals that depend on these native plant species, and (3) it carries a host specific disease. We performed experiments to estimate the effects of Old World and New World host-plant species and the disease on the life cycle and population growth of the cinnabar moth. An insect is expected to shift host plants if fitness is higher on non-target compared to target host-plants, perhaps because the advantage of reduced effectiveness of insect natural-enemies outweighs the disadvantage of insect malnutrition associated with non-target host-plants. Contrary to this hypothesis, we found the population growth rate of the cinnabar moth is sharply reduced on non-target compared to target host-plants by interacting effects of disease and malnutrition. Ironically, a pathogen of the cinnabar moth may enhance weed biological-control by providing insurance against host-shifts onto native non-target host plants.

Technical Abstract: The cinnabar moth (Tyria jacobaeae (L.), Lepidoptera: Arctiidae) is an icon in population ecology and biological control that has recently lost its shine based on evidence that (1) it is less effective than alternatives (such as the ragwort flea beetle Longitarsus jacobaeae (Waterhouse) (Coleoptera: Chrysomelidae) for controlling ragwort, Senecio jacobaea L. (Asteraceae), (2) it eats (harms) non-target plant species (including arrowleaf ragwort, Senecio triangularis Hook. (Asteraceae), a native North American wildflower), and potentially harms the animals that depend on these native plant species, and (3) it carries a disease (caused by a host-specific microsporidian Nosema tyriae). We used a Life Table Response Experiment combining a factorial experiment and a matrix model to estimate the independent and interacting effects of Old World and New World host-plant species (1st trophic level) and the entomopathogen (3rd trophic level) on the life cycle and population growth of the cinnabar moth (2nd trophic level). Host shifts are expected if herbivore fitness is higher on novel compared to conventional host-plants, perhaps because the advantage of reduced effectiveness of herbivore natural-enemies outweighs the disadvantage of herbivore malnutrition associated with novel host-plants. Contrary to this hypothesis, we found the population growth rate of the cinnabar moth is sharply reduced on novel compared to conventional host-plants by interacting effects of disease and malnutrition. Paradoxically, a pathogen of the cinnabar moth may enhance weed biological-control by providing insurance against host-shifts.