Spatial Prediction of Habitat Overlap of Introduced and Native Thistles to Identify Potential Areas of Nontarget Activity of Biological Control Agents

Abstract

Nontarget feeding of Rhinocyllus conicus Fröelich and Trichosirocalus horridus (Panzer) on native North American thistles in the genus Cirsium has been documented. Some species of these native thistles have shown greater infestation levels of R. conicus in populations that are in close proximity to the target plant species, Carduus nutans L. In 2005 a study was initiated to identify areas of potential nontarget feeding by R. conicus and T. horridus on thistle species by predicting habitats of two known introduced hosts [C. nutans and Cirsium vulgare (Savi) Tenore] and two native species [Cirsium carolinianum (Walter) Fernald and Schubert and C. discolor (Muhlenberg ex Willdenow) Sprengel] using Mahalanobis distance (D(2)). Cumulative frequency graphs showed that the D(2) models for all four plant species effectively identified site conditions that contribute to the presence of the respective species. Poisson regression showed an association between D(2) values and plant counts at field-test sites for C. nutans and C. carolinianum. However, negative binomial regression detected no association between D(2) values and plant counts for C. discolor or C. vulgare. Chi-square analysis indicated associations between both weevil species and sites where C. vulgare and Carduus nutans were found, but not between the weevil and native thistle species. Habitats of C. nutans and Cirsium carolinianum overlapped in ≈12% of the study area. Data-based habitat models may provide a powerful tool for land managers and scientists to monitor native plant populations for nontarget feeding by introduced biological control agents.

Phylogeny of Cirsium spp. in North America: Host Specificity Does Not Follow Phylogeny

“…Prediction of non-target host selection for R. conicus would not have identified the native thistle C. canescens as a host plant based on plant morphology and the phylogenetic relationships ( Figure 1 ). Likewise, prediction of non-target host selection for the foliar feeder Trichosirocalus horridus , which also was introduced from Europe into the U.S. in late 1960s as biological control agent for C. nutans [ 35 ], may not have identified the potential for foliar damage observed on North American native thistles C. altissimum , C. discolor , and C. carolinianum [ 36 ]. It is now known that various ecological factors like habitat preference of the biological control agent and geographical proximity to related plants provide better cues to potential alternative hosts [ 32 , 36 , 37 , 38 ].…”

Nontarget herbivory by a weed biocontrol insect is limited to spillover, reducing the chance of population‐level impacts

“…Regardless if spillover is temporary or continuous, this pattern of nontarget herbivory creates a spatial refuge for nontarget plants away from any situation of high weevil density. The extent of such refuges may be a function of the insect's reduced host-finding and arrestment behaviors for nontargets (Catton et al 2014), and the degree of non-overlap in plant distributions (Wiggins et al 2010) and suitable agent habitat (Andres 1985, Diehl andMcEvoy 1989). Identifying the level of spatial isolation required for refuge formation is a logical next step in exploring this phenomenon; withinpatch spatial analysis of herbivory on our experimental release sites indicate that spatial refuges could occur less than 5 m from release points (Catton et al 2014).…”

Remote Distinction of A Noxious Weed (Musk Thistle: CarduusNutans) Using Airborne Hyperspectral Imagery and the Support Vector Machine Classifier

“…One non-native weed of major ecological and economic importance in the US, Canada, Australia, New Zealand and southern Africa is musk thistle or nodding thistle (Carduus nutans L.), an aggressive member of the sunflower (Asteraceae) family that is native to North Africa and Eurasia [17][18][19][20][21][22]. Musk thistle infests a considerable amount of land area in the US (found in 45 states) and Canada (found at least in five provinces) and has a long history in these countries as an invasive species [20,21].…”

“…Musk thistle infests a considerable amount of land area in the US (found in 45 states) and Canada (found at least in five provinces) and has a long history in these countries as an invasive species [20,21]. Musk thistle has been declared a noxious weed in many US states, Canadian provinces and Australia.…”