Evaluation of ecological risk to populations of a threatened plant from an invasive biocontrol insect

S. M. Louda; T. A. Rand; A. E. Arnett; A. S. McClay; A. K. McEachern

doi:10.1890/03-5212

Home/Archive/USGS

USGS · 1008192

Evaluation of ecological risk to populations of a threatened plant from an invasive biocontrol insect

S. M. Louda·T. A. Rand·A. E. Arnett·A. S. McClay·A. K. McEachern

View original source ↗Export metadata ↓

Abstract

Controversy exists over estimation of ecological risk in biological control. At present, the risk to the rare, federally listed Pitcher's thistle ( Cirsium pitcheri ) in North America from Rhinocyllus conicus , a biological control weevil now feeding on many native thistles, is unknown. We hypothesized that quantification of host specificity and potential phenological overlap between insect and plant would improve assessment of the magnitude of risk. In laboratory host specificity tests, we found no significant difference in R. conicus feeding or oviposition preference between the rare C. pitcheri and the targeted exotic weed ( Carduus nutans ) or between C. pitcheri and Platte thistle ( C. canescens ), a closely related native North American species known to be affected by R. conicus . In a garden environment, R. conicus spontaneously found, oviposited, and developed completely on C. pitcheri . Taller plants with more flower heads were significantly more vulnerable, suggesting that the greatest impact is likely to be on individuals that generally contribute the most to recruitment and population persistence. For eight sites in two national parks over three years, the calculated period of expected R. conicus activity overlapped 99% and 78% of the flower heads initiated by C. pitcheri in the southern and the northern park, respectively. A demographic model suggests that population growth rate (λ) of C. pitcheri will decrease from 0.9897 to 0.8686, while time to halve the population will decrease from 66.9 to 4.9 years, under the conservative assumption that oviposition by R. conicus on C. pitcheri will occur at the same rate as on the related C. canescens . Calculated decreases in λ and t 0.5 are larger if the rate of oviposition actually observed in the laboratory tests is used. These results indicate that the weevil poses a serious quantitative, demographic risk to the threatened C. pitcheri . The study supports the suggestion that ecological data can be used to improve the quantification of risk to native nontarget plant populations within the potential physiological host range of a biological control insect.

Explore related subjects

Ecological Applications Article

Source-reported bounding extent: 17.94655° to 83.23324° latitude; -171.79111° to -52.6481° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

S. M. Louda, T. A. Rand, A. E. Arnett, A. S. McClay, A. K. McEachern. 2005. Evaluation of ecological risk to populations of a threatened plant from an invasive biocontrol insect. https://doi.org/10.1890/03-5212

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2026

Malady in motion: Chronic wasting disease effects on host movement

Pathogens can have significant impacts on host movement and behavior with consequences for ongoing transmission. For example, chronic wasting disease (CWD) causes severe nutritional deficiencies and neurologic changes, which may alter white-tailed deer ( Odocoileus virginianus ) movement and subsequent transmission risk. Our objectives were to test for changes in movement and habitat selection in deer affected by CWD, and determine the timing of any changes we observed. We leveraged comprehensive movement and mortality data from a large study of free-ranging deer in southwest Wisconsin, a region with high prevalence of CWD. We used necropsy data to identify end stage CWD cases with movement data leading up to death ( n = 44), and sex-, date-, and age-matched test-negative controls. Using GPS collar data, we identified extra-home range excursions and tested for differences in excursion rates, distances, and durations between cases and controls. We evaluated movement characteristics (e.g., movement rates, weekly range sizes) and habitat selection for the two groups, using change point analysis to determine when behavior changes occurred during disease progression. Excursion distances were reduced for CWD cases but were otherwise largely unaffected by infection status. However, CWD cases moved at slower rates and maintained smaller ranges than controls. Habitat selection varied minimally between cases and controls, though CWD cases had an increased preference for proximity to forest edges. While changes in case movement rates and range sizes were detected at or before 6 months prior to death, other movement and habitat selection changes appeared about 2 months prior to death. In addition, CWD cases were frequently in good body condition even within 6 months prior to death, implying that clinically apparent changes occur very late in the disease progression. Our results suggest the occurrence of subclinical and clinical phases of infection, beginning around 6 and 2 months prior to death, respectively. Public communication may therefore benefit from emphasizing that CWD-infected deer are infectious long before they appear sick. Further, because most movement changes occur for very short periods relative to the infectious period of CWD, typical healthy deer movement is likely adequate for representing transmission dynamics for surveillance and management planning.

Wisconsin↗

USGS2026

Improving predictions of insect harassment for barren-ground caribou in the Arctic

Many populations of barren-ground caribou ( Rangifer tarandus ) have declined or are declining, which is concerning given their ecological role in Arctic ecosystems and their societal role in northern communities. Insect harassment is an important driver of the behavior, energetics, and demographic rates of caribou, and yet, due to challenges in predicting harassment, there is limited understanding of how it is responding to changing Arctic conditions. We investigated environmental correlates of mosquito (Culicidae) and oestrid fly (Oestridae) harassment for the Porcupine caribou herd, with the aim of improving our ability to predict harassment. We collected field observations of mosquito activity and used video collars to detect oestrid fly activity across the summer range, which spans the Alaska–Yukon border. Additionally, we documented the composition of harassing insects collected in malaise traps using DNA metabarcoding. We developed predictive mosquito and oestrid fly harassment models using remotely sensed variables relevant to the insects' biology within a nonlinear modeling framework. We then used the top mosquito and oestrid fly models to hindcast predictions of harassment during 1950–2024 and investigate long-term changes in severity and phenology. The top mosquito harassment model included wind speed, temperature, days since snowmelt, precipitation, topographic position, and soil moisture. The top oestrid fly harassment model included temperature, cumulative growing degree days, and time of day. Harassment of both insects was limited at low temperatures (<10°C), with mosquitoes being additionally limited at high temperatures (>22°C) and wind speeds (>7 m/s). The phenology of mosquito and oestrid fly harassment exhibited curvilinear trends across the summer, peaking in midsummer based on the number of days since snowmelt and cumulative growing degree days, respectively. Mosquito harassment also increased with greater soil moisture, precipitation, and at lower relative elevations. Hindcasting indicated that insect harassment notably intensified and advanced over time. Intensifying harassment could decrease caribou foraging opportunities and body condition, and advancing harassment is likely to increasingly overlap with the calving season when calves are most vulnerable. Our results highlight climate-driven changes in insect harassment and provide improved indices for predicting harassment in the Arctic for future applications.

Alaska↗

USGS2026

Application of close-kin mark–recapture to an American black bear population using harvest samples

Close-kin mark–recapture (CKMR) offers a promising alternative to traditional mark–recapture methods for estimating wildlife population parameters. CKMR estimates demographic parameters by identifying genetic relationships between individuals, effectively “recapturing” parental genotypes through their offspring's genetic profiles. One key advantage of CKMR over traditional methods is the ability to estimate abundance without recapture, facilitating the use of lethally collected biological samples. Here, we present an application of CKMR to a terrestrial species using samples collected from harvested individuals. We analyzed genetic data from 1767 American black bears ( Ursus americanus ) harvested over two consecutive years in Michigan's Upper Peninsula. Using Genotyping-in-Thousands by sequencing (GT-seq), we identified parent-offspring pairs and developed sex-specific models tailored to black bear reproductive biology and management strategies. Female population estimates aligned with our expectations, based on prior knowledge of the population. In contrast, male population estimates deviated from expectations, potentially due to an unmodeled combination of factors pertaining to male reproductive biology and sampling bias. Our study not only demonstrates the viability of using harvest-based CKMR for monitoring of terrestrial wildlife populations, but also highlights the need for careful model specification. By providing a novel method to estimate demographic parameters and population size, CKMR using harvest samples can inform management decisions and harvest quotas. This approach leverages existing management practices involving collection of genetic samples, such as mandatory harvest registrations and health monitoring programs. Our findings contribute to the growing body of CKMR applications and expand its use to terrestrial species management.

Michigan↗