The cinnabar moth, Tyria jacobaeae (L.) (Lepidoptera:Arctiidae), was
released in 1959 to control the grassland weed tansy ragwort, Senecio jacobaea L.
(Asteraceae), despite evidence that caterpillars of this species can feed on native
plants within the genera Senecio and Packera. Previous studies confirmed the
moth's ability to develop on the native Senecio triangularis Hook., although no
systematic study has been conducted to determine the extent of non-target impact
on all potential host species. To address the lack of systematic studies we
conducted a regional survey to determine the consequences of exposure of non-target
plants to cinnabar moth caterpillars. We also conducted a local field
experiment to determine the influence of habitat on the patterns of association of
the moth and non-target plants.
In the regional survey, we mapped the potential distribution of the cinnabar
moth in Oregon to determine the extent of exposure of native Senecio and Packera
species, and systematically sampled exposed species to assess the frequency and
severity of feeding on these plants. We found that nine of the 20 native non-target
species in Oregon were exposed to the cinnabar moth, three of the 10 native
Senecio and six of the 10 native Packera. Ten of the native species escaped
exposure because they occur east of the Cascade Mountain Range where the
cinnabar moth does not occur. We found feeding damage on three of the nine
exposed species: Packera cymbalarioides, P. pseudaurea, and S. triangularis were
attacked at one of three (33%), two of six (33%), and seven of 15 (47%) sites that
supported populations of each species, respectively. Within sites, attack frequency
of stems was 33% (of six total stems sampled) for P. cymbalarioides, and ranged
from 53% to 56% (of 20 to 108 total stems sampled) for P. pseudaurea and 7% to
64.5% (of 32 to 458 total stems sampled) for S. triangularis. Conditional median
damage per site (median of attacked stems only) was 10% in P. cymbalarioides,
5% to 17.5% in P. pseudaurea, and 5% to 37.5% in S. triangularis. The attack rate
on non-target plants (7.1 to 64.5 percent of stems attacked at a singe site) was equal
to or greater than on the target weed (8.3 to 50.0 percent of stems attacked at a
single site). At three sites, caterpillars attacked non-target plants but the target
weed was absent, and at one site, the target was present but caterpillars fed on non-target
plants only. We conclude that attack frequency and severity on the three
species is not high, but equaled or exceeded the level of attack on the target weed.
We also conducted a mark-release-recapture experiment to relate habitat
preference to patterns of non-target host use in the field. We compared adult moth
dispersal patterns and larval development between a meadow habitat and a forest
habitat. We found that long-term dispersal distance (spanning days) was similar in
both habitats but we recaptured a higher percentage of moths from the meadow
(47%) compared to the forest (10%). Short-term displacements, based on direct
observations of flights immediately after release, differed between habitats: moths
in the meadow flew short distances (8.5m ± 1.5, n=13) at or below the
herbaceous canopy (0.8 m ± 0.2, n=13) while moths in the forest flew longer
horizontal (22.8 m ± 2.8, n=15) and vertical distances (5.9 m ± 0.9, n=15). We
recovered seven fifth instar larvae (of 278 eggs) from the meadow habitat but no
larvae beyond the second instar (of 119 eggs) were recovered from the forest
habitat. We conclude that the cinnabar moth is limited to meadow habitats because
adult moths display movement patterns that remove them from forest habitats
(possibly due to disorientation) and larvae are unable to survive on plants growing
in the forest.
Taken together, the regional survey and the local field-experiment indicate
that the cinnabar moth uses only a small proportion of available non-target host
plant species. Other species are likely unused because of geographic isolation from the moth, habitat selection by the moth, or phenological differences between the
moth and non-target plants. / Graduation date: 2003
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29913 |
| Date | 22 August 2002 |
| Creators | Fuller, Jason L. |
| Contributors | McEvoy, Peter B. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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