DOI: 10.5061/dryad.v9s4mw711
title: Data for: Implications of climate change for biocontrol efficacy across the northern range of the invasive plant Linaria dalmatica

description: The effect of insect biological control agents on invasive plant
 populations can vary spatially, and spatial variation in climate may drive
 regional variation in herbivory, and thus biocontrol efficacy. Within host
 plant populations, local plant abundance can also be affected by the
 spatial distribution of herbivores, but whether local patterns persist at
 larger scales is less well understood. We examined how infestation and
 damage of the stem-mining weevil Mecinus janthiniformis, a specialist
 biocontrol agent of the invasive plant Linaria dalmatica, varied with and
 among populations across the northern edge of the range in North America.
 We quantified weevil and invasive plant densities, as well as plant
 fecundity, stem diameter and height across sites spanning an area of
 ~39,000 km2 in British Columbia, Canada. We found that specialist weevils
 did not respond to host plant density within sites across the study
 region. Instead, weevil attack and load were most sensitive to among-site
 variability in climate, with stems at warmer sites have four times as many
 weevils compared to stems at cooler sites. Weevils also reduced plant
 fecundity more at warmer sites, when controlled for plant size (stem
 diameter) with larger effects of weevils in thicker stems, indicating that
 L. dalmatica suppression is highest in warmer locations where weevils are
 more abundant and environmental conditions more favorable. Our results
 suggest that, with climate change, the efficacy of biocontrol for L.
 dalmatica will improve across the northern edge of the range. We recommend
 that at cooler sites, where biocontrols are less prevalent and effects on
 plant fecundity are weaker, alternative management strategies are
 necessary at this time. Across invasive plant species more generally,
 future studies that establish the role of climate in variability in
 biocontrol efficacy long after introduction can improve management of
 invasive plants under climate change.
description: We surveyed <em>L. dalmatica</em> populations across
 a wide swath of British Columbia, on the eastern side of the Canadian
 Cascade mountains in the summer of 2017, encompassing an area of
 approximately 39,000 km<sup>2</sup> (Figure 1, Table A1). In
 consultation with local invasive plant managers and data from the British
 Columbia Invasive Alien Plant Program (B.C. Ministry of Forests, Lands and
 Natural Resource Operations, 2017), we selected sites where no active
 management, e.g. herbicide spray or mowing, was planned for 2017, with the
 goal of sampling as broadly as possible. Since <em>L.
 dalmatica</em> populations respond positively to disturbance (Sing
 et al., 2016), our goal was to choose sites of similar levels of
 disturbance, and all sites were located within 100 meters of primary or
 secondary roads. 39 sites were used in the analyses (those we were able to
 access in late summer to collect stems) and data from those sites are
 included here. In the field, we surveyed stem density
 in 1x1 m<sup>2</sup> plots - and counted vegetative and
 flowering stems separately. Later in the summer, we collected at least 20
 stems from each site (10 from low density and 10 from high density plots)
 to bring back to the lab to quantify size, seed production, and dissect to
 count <em>Mecinus janthiniformis</em> individuals (the
 biological control). Please see Methods for details of data collection and
 analyses.
description: No proprietary programs required (all data in the mansucript were
 viewed and analyzed in R).