Data from: Nontarget herbivory by a weed biocontrol insect is limited to spillover, reducing the chance of population-level impacts

Insects approved for classical biocontrol of weeds are often capable of using close relatives of their target weed for feeding, oviposition, or larval development, with reduced preference and performance. When nontarget herbivory occurs and is suspected to reduce survival, growth, or fecundity of individual plants, and insects are capable of reproducing on their nontarget host, characterization of spatial and temporal patterns of the occurrence and intensity of herbivory is valuable for predicting potential population-level effects. Here, we perform a novel post-release manipulative field experiment with a root-feeding biocontrol weevil, Mogulones crucifer, released in Canada to control the rangeland weed Cynoglossum officinale, to test for its ability to establish on the nontarget plant Hackelia micrantha. After Cynoglossum, M. crucifer exhibits its highest preference for and performance on Hackelia spp. We released M. crucifer on Canadian rangeland sites with naturally occurring populations of H. micrantha growing interspersed with the target weed or in the near absence of the target weed. Adult weevil feeding on surrounding plants was monitored for three summers after release (years 0, 1, and 2), and, subsequently, subsets of plants were destructively sampled to determine M. crucifer oviposition levels. Additional oviposition and larval development data were obtained from seven non-experimental sites where weevils were released zero, three, or four years earlier. M. crucifer was not detected on experimental sites without C. officinale after two years, and nontarget herbivory was restricted to rare, low-level spillover. Visible evidence of adult herbivory (i.e., scars on shoots) was associated with oviposition in 90% of targets but only 30% of nontarget plants. We infer, through ecological refuge theory, that nontarget population-level impacts from M. crucifer spillover are unlikely because of temporal, spatial, and probabilistic refuges from herbivory, and make recommendations for monitoring and management of biocontrol systems with similar attributes, such as removing target plants around nontarget populations of interest. Because M. crucifer is among the least host-specific of the modern weed biocontrol agents, and H. micrantha is likely one of its most highly preferred nontargets, these conclusions are, arguably, generally applicable to other nontarget plants and biocontrol systems.Catton et al Fig 1 data June 8 2013This data file was used to generate Figure 1 in Catton et al. (2015). It contains the results for the presence or absence of M. crucifer herbivory scars on Cynoglossum officinale and Hackelia micrantha plants target common or target rare sites (where applicable) in years 0, 1, and 2 following a point release of 300 M. crucifer on each site on 4 June 2009.Catton et al Fig 2 data June 10 2013This data file was used to generate Figure 2 in Catton et al. (2015). It contains the results of dissectionsfor M. crucifer eggs and larvae in Cynoglossum officinale and Hackelia micrantha plants on M. crucifer release sites where both plant species were present.Catton et al Fig 3 data June 17 2013This data file was used to generate Figure 3 in Catton et al. (2015). It contains the results of dissection for M. crucifer eggs and larvae in Hackelia micrantha plants relative to the level of C. officinale herbivory on each site, expressed as the back-transformed mean ln(number of eggs per C. officinale plant +1) on M. crucifer release sites where both plant plant species were present.Catton et al Fig 4 data June 4 2014This data file was used to generate Figure 4 in Catton et al. (2015). It contains the results of dissection for M. crucifer eggs and larvae in Cynoglossum officinale and Hackelia micrantha plants on release sites in years where M. crucifer was known to be present.Experimental Release Site dissections after 2 years Dec 7 2014This data file was used to test for M. crucifer population establishment on experimental target common and target rare release sites after 2 years. It displays Cynoglossum officinale and Hackelia micrantha plants sampled and dissected in search of M. crucifer eggs and larvae. Plants were kept refrigerated between harvest and dissection, and whole plants were dissected