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Abstract:
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Background/Question/Methods Rare organisms are often strongly affected by chance, disease, invasive species, and other factors. Pieris virginiensis (Pieridae), a rare woodland butterfly, flies only in April and May, in often unsuitable weather, and uses native mustards as its primary larval hosts. P. virginiensis may be adversely affected by the introduction of the invasive garlic mustard and other biotic and abiotic stressors. A. petiolata, which contains feeding deterrents, has been observed as an oviposition site for P. virginiensis. We reexamined a population of P. virginiensis in Ohio that uses A. laevigata as its primary host. This population was last studied in the 1988, prior to the introduction of A. petiolata to the area. We sought to test the hypothesis that A. petiolata introduction has changed P. virginiensis oviposition behavior. On April 28, 2011, we marked 64 flowering stems of A. laevigata and 54 flowering stems of A. petiolata in the exact location where the previous study was performed and examined them weekly for eggs, larvae, herbivore damage, and other observations. We recovered no P. virginiensis eggs or caterpillars, observed no Pieris-specific damage on monitored plants, and we failed to observe any butterflies. To examine alternative stressors on the butterfly or host populations, we recorded general damage, deer browsing, and the presence of possible larval predators. Although the invasive A. petiolata is well established at this site, we believe that the primary cause of butterfly mortality for 2011 was weather, with Columbus, Ohio reaching a new record of 18.1 cm precipitation from April 1-28. From 4/1-5/12, only 33% of the days were marginally acceptable for adult flight (wind < 6.7 m/s, temp. > 10 o C). We conclude that despite pressures due to invasion, predation, and deer browsing, poor flying conditions were the primary stressor in 2011 and apparently prevented any successful reproduction of this butterfly in this area. |
