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Abstract Detail

Conservation Biology

Deprenger-Levin, Michelle [1], Grant III, Thomas A. [1], Dawson, Carol [2].

Impacts of the Introduced Biocontrol Agent, Rhinocyllus conicus, (Coleoptera: Curculionidae) on Fruit Production and Population Dynamics of a Rare, Native Thistle, Cirsium ownbeyi Welsh (Asteraceae).

The release of non-native biocontrol agents to treat noxious weeds can be an efficient and effective way to combat invasions without disturbing the environment through chemical or mechanical methods. However, pre-release studies of insect biocontrol agents that indicate a generalist feeding habit have, in some cases, failed to predict the extent of damage to non-target species in their environment. From 1998 to 2005 we studied the non-target effects of an introduced weevil, Rhinocyllus conicus, on Cirsium ownbeyi, a rare native thistle of northwestern Colorado, northeastern Utah, and southwestern Wyoming. Rhinocyllus conicus was introduced to control musk thistle (Carduus nutans L.) and several closely related species though it was known to utilize several North American native species within genera Cirsium, Silybum and Onopordum. In the spring, the adult weevil oviposits eggs on the outside of developing inflorescencesí involucral bracts. When the eggs hatch, the larvae burrow through the bracts into a head of florets where they pupate and feed on developing ovules. The biocontrol has infested 35% of all capitula in the study plots and the average number of boring holes did not change significantly over the years (p = 0.152). Weevil damage is not influenced by climate or number of flowering individuals. Despite evidence that this biocontrol agent uses many native Cirsium species and that the frequency of use is increasing, no decrease in C. ownbeyi could be related to ovule damage by R. conicus. However, increased seed predation due to R. conicus may have long-term repercussions for this perennial plant that are not detectable in the eight years of this project. These populations may be stable in the short-term but reduced seed production poses a definite threat for long-term survival of this rare species.

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1 - Denver Botanic Gardens, Research, 909 York Street, Denver, CO, 80206, USA
2 - U.S. Bureau of Land Management (BLM) - Colorado State Office, 2850 Youngfield Street, Lakewood, CO, 80215, USA

Biological control
non-target effects
Rhinocyllus conicus
Carduus nutans
Cirsium ownbeyi
seed predation.

Presentation Type: Poster:Posters for Topics
Session: P
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM
Number: P65005
Abstract ID:1716

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