Terrestrial invasive species threaten the integrity of diverse and highly-valued ecosystems. The Minnesota Invasive Terrestrial Plants and Pests Center (MITPPC) was established by the state of ...Minnesota to fund research projects aimed at minimizing harms posed by the most threatening terrestrial invasive species to the state's prairies, wetlands, forests, and agriculture. MITPPC used the Analytic Hierarchy Process (AHP) to identify and prioritize diverse invasive species threats. We describe how MITPPC tailored AHP to establish its research priorities and highlight major outcomes and challenges with our approach. We found that subject matter experts considered factors associated with the severity of impact from invasion, rather than the potential for invasion, to be the greatest contributors in identifying the most threatening species. Specifically, out of the 17 total criteria identified by the experts to rank species, negative environmental impact was the most influential threat criterion. Currently, narrowleaf cattail, mountain pine beetle, and the causative agent of Dutch elm disease are top threats to Minnesota terrestrial ecosystems. AHP does not handle data-poor situations well; however, it allows for easy incorporation of new information over time for a species without undoing the original framework. The MITPPC prioritization has encouraged interdisciplinary, cross-project synergy among its research projects. Such outcomes, coupled with the transparent and evidence-based decision structure, strengthen the credibility of MITPPC activities with many stakeholders.
•Expert opinions differ about the threat posed by terrestrial invasive species.•The Analytic Hierarchy Process organized expert opinions into decision-support criteria.•Threat level was driven by impact of invasion more than the potential for invasion.•Environmental impacts were more important than economic impacts for ranking threats.•Decision transparency and consistency increase credibility with stakeholders.
Drosophila suzukii Matsumura, often called spotted wing drosophila, is an exotic vinegar fly that is native to Southeast Asia and was first detected in the continental United States in 2008. Previous ...modeling studies have suggested that D. suzukii might not survive in portions of the northern United States or southern Canada due to the effects of cold. As a result, we measured two aspects of insect cold tolerance, the supercooling point and lower lethal temperature, for D. suzukii summer-morph pupae and adults and winter-morph adults. Supercooling points were compared to adults of Drosophila melanogaster Meigen. The lower lethal temperature of D. suzukii winter-morph adults was significantly colder than that for D. suzukii summer-morph adults, while supercooling points of D. suzukii winter-morph adults were actually warmer than that for D. suzukii summer-morph adults and pupae. D. suzukii summer-morph adult supercooling points were not significantly different than those for D. melanogaster adults. These measures indicate that D. suzukii is a chill intolerant insect, and winter-morph adults are the most cold-tolerant life stage. These results can be used to improve predictions of where D. suzukii might be able to establish overwintering populations and cause extensive damage to spring fruit crops.
Nematodes play significant roles in carbon and nitrogen biogeochemical cycles in soils. The contributions of individual species to these processes depend, in part, on differences in their population ...ecology. Formatting errors were discovered that made portions of our previously published work on this subject nearly unintelligible. Herein, we correct those errors.
•Nematodes play significant roles in carbon and nitrogen biogeochemical cycles in soils.•The contributions of individual species to these processes depend, in part, on differences in their population ecology.•Formatting errors were discovered that made portions of our previously published work on this subject nearly unintelligible.•Herein, we correct those errors.
We tested the hypotheses that management of the soil food web in the fall would enhance grazing on bacteria and fungi by microbivorous nematodes in the spring, consequently increasing N availability ...in cover-crop driven organic and low-input farming systems. The food web was manipulated by irrigating the dry soil of late summer and/or providing carbon sources. By creating conditions conducive for biological activity, we increased the abundance of bacterivore and fungivore nematodes in the fall and the following spring. Greater biological activity in the soil enhanced concentrations of mineral N available to the subsequent summer tomato crop. Mineral N concentration in the spring was associated with abundance of bacterivore nematodes, and with the corresponding Enrichment Index (EI) provided by nematode community analysis. Because environmental conditions that favour increase of bacterivore nematodes probably also favour other microbial grazers, including protozoa, the abundance of bacterivore nematodes may be an indicator of overall grazing activity and N mineralisation rates from soil fauna. Decomposition pathways in the spring, inferred from nematode bioindicators, were dominated by bacteria in plots that had been irrigated the previous fall while fungi were more prevalent in those that had not. The responses of omnivore and predator nematodes to our treatments were not consistent and there was no evidence that regulation of opportunist species by predators would be enhanced by the management practices imposed.
The increasing economic and environmental losses caused by non-native invasive species amplify the value of identifying and implementing optimal management options to prevent, detect, and control ...invasive species. Previous literature has focused largely on preventing introductions of invasive species and post-detection control activities; few have addressed the role of detection. By increasing resources to detect invasive species, managers may increase their chances of finding a species at a smaller population level, lessening the extent of damages and making subsequent control potentially less expensive and more effective. However, detecting new invasive species is difficult and uncertain; many factors reduce the likelihood of successful detection, such as low population densities which are prevalent in invasive species management. This paper presents a model that captures the stochastic and dynamic aspects of this trade-off by incorporating a detection stage in which the agency managers choose search effort prior to the post-detection control stage. The analysis of the model illustrates that the optimal detection strategy depends primarily on the ‘detectability’, or ease of detection, and the biological relationships of each distinct species.
The invasion of soybean aphid, Aphis glycines Matsumura, into soybean (Glycine max L.) production areas of the northcentral United States has generated substantial concern over the ultimate impact of ...this pest on domestic agriculture. To evaluate the potential extent and severity of its invasion in the United States, we examined possible pathways for the arrival of the insect, considered the likelihood for establishment in different regions of the United States, and described patterns of spread. Historical records of aphid interceptions by the U.S. Department of Agriculture, Animal and Plant Health Inspection Service suggest that populations of soybean aphid most likely arrived in the United States from Japan or China, either carried by an international airline passenger or associated with horticultural cargo. Two methods of climate comparison suggest that the aphid may ultimately be present in all soybean producing areas of the United States. However, the severity of infestations within these areas is likely to vary considerably in space and time.
An insect's cold hardiness affects its potential to overwinter and outbreak in different geographic regions. In this study, we characterized the response of Helicoverpa zea (Boddie) pupae to low ...temperatures by using controlled laboratory measurements of supercooling point (SCP), lower lethal temperature (LT50), and lower lethal time (LLTime). The impact of diapause, acclimation, and sex on the cold hardiness of the pupae also were evaluated. Sex did not significantly affect the SCP, LT50, or LLTime. However, the mean SCP of diapausing pupae (-19.3°C) was significantly lower than nondiapausing pupae (-16.4°C). Acclimation of nondiapausing pupae to constant temperatures from 10 to 20°C before supercooling also produced a significantly lower SCP than nondiapausing pupae held at 25°C. The LT50s of nondiapausing and diapausing were not significantly different, but confirmed that H. zea pupae are chill-intolerant because these lethal temperatures are warmer than the corresponding mean SCPs. Diapausing pupae survived longer than nondiapausing pupae at the same, constant, cold temperatures, a finding consistent with the SCP results. Both of these results suggest enhanced cold hardiness in diapausing pupae. When laboratory results were compared with field temperatures and observed distributions of H. zea in the contiguous United States, the laboratory results corroborated what is currently perceived to be the northern overwintering limit of H. zea; approximately the 40th parallel. Moreover, our research showed that areas north of this limit are lethal to overwintering pupae not because of low temperature extremes, but rather the length of time spent at near-zero temperatures.
► Shoot blight disease limits development of multi-cohort red pine stands. ► Native pine pathogens can influence species diversity in red pine-dominated forests. ► Armillaria can increase species and ...structural diversity in red pine forests. ► The long-term risk of diseases needs to be assessed in diversifying red pine stands.
Increasing the diversity of species and structure of red pine (Pinus resinosa) is often a management goal in stands simplified by practices such as fire suppression and plantation management in many areas of the Great Lakes Region. One approach to diversification is to convert predominantly even-aged, pure red pine stands to multi-cohort, mixed-species forests through variable overstory retention at harvest. Based on limited empirical evidence, pathologists have advised against this multi-cohort approach in stands where pathogens causing damaging shoot blight diseases are established. We examined disease incidence among planted red, jack (Pinus banksiana), and white pine (Pinus strobus) in a variable retention harvest and understory woody vegetation removal (brushing) experiment in northern Minnesota. The experiment included four overstory treatments (dispersed and two aggregated overstory retention treatments and a control, N=4) that were split by an understory brushing treatment (yes or no). Prior to harvest in 2003, the fungal pine pathogens Diplodia pinea, Sirococcus conigenus and Armillaria solidipes (syn. Armillaria ostoyae) were common on the study site. Within 6years after harvest, these pathogens reduced the survival of planted red, white and jack pine, potentially interfering with long-term management objectives. Across all treatments, shoot blight incidence was generally higher in dead red and jack pine than white pine seedlings and was predominantly caused by D. pinea. The disease killing white pine seedlings was predominately Armillaria root rot. Overstory treatment affected the percentage of jack and white pine seedling mortality attributable to shoot blight, but not the more susceptible red pine, with greater overstory retention resulting in greater disease incidence. Understory brushing had no effect on the incidence of shoot blight on seedlings. We expect disease to continue to influence stand structure and composition across all treatments. Our study results highlight the need for forest managers to assess long-term risk of potentially damaging pathogens in red pine stands prior to harvest and use that information to guide decisions regarding silvicultural practices to increase age and species diversity.
Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), reached damaging levels in 2003 and 2005 in soybean, Glycine max (L.) Merrill, in most northern U.S. states and Canadian provinces, and ...it has become one of the most important pests of soybean throughout the North Central region. A common experimental protocol was adopted by participants in six states who provided data from 19 yield-loss experiments conducted over a 3-yr period. Population doubling times for field populations of soybean aphid averaged 6.8 d plus or minus 0.8 d (mean plus or minus SEM). The average economic threshold (ET) over all control costs, market values, and yield was 273 plus or minus 38 (mean plus or minus 95% confidence interval CI, range 111-567) aphids per plant. This ET provides a 7-d lead time before aphid populations are expected to exceed the economic injury level (EIL) of 674 plus or minus 95 (mean plus or minus 95% CI, range 275-1,399) aphids per plant. Peak aphid density in 18 of the 19 location-years occurred during soybean growth stages R3 (beginning pod formation) to R5 (full size pod) with a single data set having aphid populations peaking at R6 (full size green seed). The ET developed here is strongly supported through soybean growth stage R5. Setting an ET at lower aphid densities increases the risk to producers by treating an aphid population that is growing too slowly to exceed the EIL in 7 d, eliminates generalist predators, and exposes a larger portion of the soybean aphid population to selection by insecticides, which could lead to development of insecticide resistance.
Invasive alien plant pests and diseases pose a threat to agriculture and biodiversity worldwide.Pathway models are an emerging tool for assessing introduction risks and evaluating risk reduction ...options.A classification of pathway models is presented, based on their mathematical form.Flow-based and agent-based models are discerned, and models with and without stochasticity.The key challenge for the future of pathway modelling is the collection of quality data to allow parameterization.
Alien plant pests are introduced into new areas at unprecedented rates through global trade, transport, tourism and travel, threatening biodiversity and agriculture. Increasingly, the movement and introduction of pests is analysed with pathway models to provide risk managers with quantitative estimates of introduction risks and effectiveness of management options. Pathway models vary greatly in mathematical form, level of detail, treatment of uncertainty and variability, as well as terminology. We conducted an overview and cluster analysis of pathway models to guide risk assessors, risk managers and model developers. We performed divisive hierarchical clustering on models retrieved from the peer-reviewed and grey literature to characterise and categorize the currently used modelling approaches. We distinguish two clusters of models based on product volume flows and two clusters of models based on the movement of individual agents. The first cluster of flow-based models describes a flow of infested material from origins to destinations according to fixed partitioning coefficients. These deterministic models can account for consequences of parameter variability and uncertainty. The second and third clusters of pathway models incorporate stochasticity in processes, and are respectively flow-based or agent-based. Models in the fourth cluster account for interactions between agents and nodes in the pathway. Conceptually, there are no fundamental differences between epidemic network models and this last cluster of pathway models. The choice of pathway model depends on the aim of the risk assessment, the available time, expertise and data. Models in clusters 2, 3, and 4 add sophistication and insight in variability to pathway analysis, but under time and data constraints, key objectives of risk assessors and managers can be addressed with models in cluster 1. The four clusters represent a comprehensive and fit for purpose toolbox of models.
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