Assessment of Pollinator Preference of Native and Nonnative Perennial Flowering Plants in South Dakota’s Grasslands

With global pollinator decline continually worsening as a result of human action, concerned citizens and scientists alike have been looking for answers as to what can be done to help, and the question of whether native or non-native plants provide more benefit to pollinating insects has been long discussed in the scientific community. This research is intended to help answer that question by attempting to determine whether pollinators have a distinct preference between native and non-native plants when presented with both options. The hypothesis at outset of this project was that native plants would provide greater benefit to pollinators, whom they (presumably) evolved alongside, and would thus be selected more frequently than non-native plants. To test this, a collection of various native and non-native plants was deployed in a restored grassland in rural South Dakota and observed for 10 days. Data collected included abundance of different groups of insect visitors and the frequency at which they visited individual plants. Analysis of data gathered during the study showed that there was no clear preference between plants based on native status alone, but rather that differences in visitation frequency possibly occurred as result of individual differences between the species of plants used, meaning that a variety of factors, not necessarily just native status, should be considered when selecting plants with the intent of encouraging pollinator activity. These results can be interpreted by ecologists to provide guidance for further research questions concerning what morphological and physiological traits attract pollinators and why, as well as conservation-minded members of the general public on what species and varieties of plants may provide the most benefit to pollinators when gardening or landscaping. In addition to the findings associated with the main research question, data also showed that pollinating insects that are not native to the study region dominated observations throughout the duration of the study, which may also have contributed to the study’s findings as well as spark further research on the relative abundance of native vs. non-native pollinators in the study area. This information could help provide more insight on the state of South Dakota’s pollinator populations and allow for more focused interpretation of the results of this study and any others like it. Introduction: The world has seen a sharp decline in pollinator (especially bee) populations in the last few decades (Goulson et al., 2015). Pollinators and other insects that utilize flowering plants play a crucial role in both ecosystem health and the ability of global food systems to produce necessary yields to feed an ever-growing population. Insect activity accounts for almost 90% of pollination done in flowering plants worldwide, with bees being responsible for a large portion of all animal-dependent pollination Assessing Pollinator Preference 2 (Winfree et al., 2010). Without bees and other pollinating insects, the world would see the loss of many flowering plants on which we and other living things depend, alongside a major drop in production of staple food crops that feed much of the world’s population. These losses could lead to both economic and humanitarian crises. Since we depend so heavily on insects to maintain ecological biodiversity and keep food production stable and diverse, there has recently been a rise in public interest about what can be done to help boost forage for pollinators, with the hopes of encouraging pollinator activity restoring population numbers. The question of whether pollinators prefer native plants over nonnative plants has been on the minds of many entomologists and restoration ecologists throughout the years, and this research sought to find an answer to that question. The hypothesis at the outset of this project was that native plants provide greater benefits to beneficial insects, and thus will be selected for more frequently than nonnative plants. The goal of this research was to find out whether native or non-native plants were more popular among pollinating insects, and if they should thus be used more frequently in landscaping and home gardening. Methods and Materials: Twelve plants were placed in a random grid, one meter apart on the inside margin of a restored grassland just outside of Volga, South Dakota (coordinates 44°22’38.72”N / -96°56’53.724”W). Plants were chosen based on bloom color (yellow, white, and purple), bloom time, and native status, with 2 plants of each species being deployed in the field. Species included nonnative Hemerocallis lilioasphodelus (HELI), Platycodon grandiflorus (PLGR), and Delphinium elatum (DEEL); and native Rudbeckia hirta (RUHI), Dalea candida (DACA), and Echinacea angustifolia (ECAN/ECPU). E. angustifolia plants were supplemented with morphologically similar, varietal Echinacea purpurea due to low bloom viability when data collection began. The white category consisting of Dalea candida and Delphinum elatum had to be excluded from data collection due to lack of blooms at the time the study was taking place, but were left in the grid for the duration of observations. Observations consisted of each plant being watched for visitation by flying insects for 3 minutes each. Any insect that encountered the pollen producing part of the plant was counted as a visitor. Counts were kept track on a handheld clicker counter and time was kept with a cell-phone timer. Visitors were categorized as ‘honeybee/syrphid’, ‘bumblebee’, or ‘other’ and the category of each individual visitor was noted by tally during the observation period. Very few butterflies and bumblebees were observed in the surrounding prairie during the study period and did not engage with the study plants at any time while observations were taking place. After data collection was complete, statistical analysis was done using ANOVA tests to measure the probability that flying insect visitors selected one category of plants more frequently than others beyond the possibility of coincidence. Analysis was done on the following variables: Individual plant species, native status, color, and native status controlled for differences in color. Insect group categories were also measured and ranked based on abundance. Assessing Pollinator Preference 3 Results: Data analysis provided mixed results depending on what variables were being considered. When species were considered independently, there was a significant difference in beneficial insect preference, with PLGR being the most selected for, followed by RUHI, then ECAN/ECPU, and lastly HELI (see figure 1). The same holds true even when controlled for color. Purple nonnative PLGR was the most selected for, and by a significant amount more, when compared to the next most popular plant, yellow native RUHI. Each of these categories were significantly more popular than purple native ECAN/ECPU, and yellow nonnative HELI, which were not significantly different from one another. When plant species were grouped based either on native status or color, there was no significant difference in insect preference (see figures 2 and 3). These results indicate that beneficial insects in the region do not prefer one color (purple or yellow) more than another, nor do they show a significant preference for either native or nonnative plants. Total visitor counts were calculated, as was the average number of visitors per plant. Visitors were categorized as either: Bumblebee, honeybee/syrphid, or other. A total of 227 individual visitors were observed during the study. 177 (77.97%) of them were honeybees or bee mimicking flies (syrphids), and 50 (22.03%) that were categorized as ‘others,’ with small beetles being the most frequently observed insects in this category. No bumblebee visitors were observed visiting any of the plants through the study’s duration. On average, each plant received 3 total visitors per observation, with 2 (66.67%) of them being in the honeybee/syrphid category, and 1 (33.33%) being ‘others. ’ Honeybees and syrphids were significantly more abundant than bumblebees and other insects according to the data analysis results. Assessing Pollinator Preference 4 Figures and Tables: ANOVA Source of Variation SS df MS F P-value F crit Between Groups 17.52101 3 5.840337 5.029023 0.003306 2.739502 Within Groups 78.97018 68 1.161326 Total 96.49119 71 0.25 1.72