Interaction of specialist root and shoot herbivores of Alliaria petiolata and their impact on plant performance and reproduction

Abstract

1. This study explored interactions of two spatially and temporally separated weevils and their impact on Alliaria petiolata (garlic mustard) survival, growth, and reproduction at different herbivore densities.2. The root‐mining weevil Ceutorhynchus scrobicollis attacks A. petiolata rosettes from October to April, and larvae complete development in May. The shoot‐mining weevil Ceutorhynchus alliariae attacks bolting plants in April/May with larvae completing development in June–July. Priority effects were expected, with early attack of C. scrobicollis affecting the later attacking C. alliariae, mediated through changes in plant growth or chemistry.3. Attack by C. scrobicollis significantly increased plant mortality and changed plant architecture, while C. alliariae only significantly reduced plant height. Attack by C. scrobicollis also increased nitrogen content of stems.4. Root feeding by C. scrobicollis affected the feeding niche of C. alliariae, but increased stem nitrogen content did not result in increased stem miner survival. While reduced height and stem diameters as a result of C. scrobicollis attack reduced C. alliariae attack at the stem level, attack at plant level and recruitment was unaffected.5. Weevil density had no effect on plant performance, most likely due to strong intraspecific competition, and there were no synergistic effects between the two herbivores.6. Overall, attack by C. scrobicollis was more detrimental to A. petiolata growth, seed output, and survival than attack by C. alliariae. Consequently, C. scrobicollis has been prioritised as a potential biocontrol agent for control of A. petiolata in North America.

The importance of space, time, and stochasticity to the demography and management ofAlliaria petiolata

“…The life cycles of C. scrobicollis and C. alliariae are documented in Gerber et al (2007b). Because it appears most likely that C. scrobicollis would be released initially (Gerber et al 2007b) with C. alliariae possibly following, we considered the effects on A. petiolata of releasing C. scrobicollis singly (one agent) and with C. alliariae (two agents) in our analyses.…”

Two Shoot-Miners,Ceutorhynchus alliariaeandCeutorhynchus roberti, Sharing the Same Fundamental Niche on Garlic Mustard

“…They clearly preferred the top part of shoots for oviposition, presumably because plant tissue is softer at the top and therefore more suitable for oviposition and development of Þrst-instar larvae. In addition, female choice might be driven partially by the higher content of nitrogen in the top shoot parts (Gerber et al 2007). The only clear difference in oviposition behavior observed was that females of C. roberti laid 40% of their eggs in clusters of up to eight eggs, whereas females of C. alliariae laid all of their eggs singly.…”

Plant-mediated interactions: Considerations for agent selection in weed biological control programs

“…With respect to introduction strategies in classical biological 83 control programs, discussion and recommendations about P-MIs apply to all situations, 84 including: (1) multiple agents being considered for importation (Gerber et al, 2007); (2) 85 additional agents considered to supplement previously imported species (Swope and Parker,86 2010); and (3) importation and release of agents in environments where resident herbivores 6 87 (either indigenous or fortuitously introduced) are present (e.g., Caesar, 2003;Hatcher, 1995;88 Moran, 2005).…”

“…Indirect P-MIs occur in plant-feeding species that are separated spatially (Blossey and Hunt-116 Joshi, 2003;Buccellato et al, 2012;Campanella et al, 2009;Hunt-Joshi and Blossey, 2005;117 Masters and Brown, 1997; Raghu et al, 2012;Simelane, 2006), temporally (Damman, 1989;118 Wold and Marquis, 1997), or both (Gerber et al, 2007;Milbrath and Nechols, 2004a;Swope and 119 Parker, 2010; Swope and Stein, 2012;Van Hezewijk and Bourchier, 2012). Thus, species that 120 interact indirectly fall into one of three categories: spatial overlap but temporal separation; 121 spatial separation but temporal overlap; spatial and temporal separation (Denno and Kaplan,122 2007; Denno et al, 1995;Ohgushi, 2005).…”

“…The studies were a mixture of greenhouse and field (including common garden) experiments, 179 and most were retrospective (i.e., they involved agents that had already been released in the 10 180 field), with the exception of Gerber et al (2007) and Raghu et al (2012) which were done 181 prospectively (i.e., prior to agent releases). Only three of the studies were conducted in the native 182 range (see Table 1).…”