Complex preference relationships between native and non-native angiosperms and foraging insect visitors in a suburban greenspace under field and laboratory conditions

Scarlett R. Howard, Matthew R. E. Symonds

The introduction and spread of non-native flora threatens native pollinators and plants. Non-native angiosperms can compete with native plants for pollinators, space, and other resources which can leave native bees without adequate nutritional or nesting resources, particularly specialist species. In the current study, we conducted flower preference experiments through field observations and controlled binary choice tests in an artificial arena to determine the impact of field vs. laboratory methods on flower preferences of native bees for native or non-native flowers within their foraging range. We conducted counts of insect pollinators foraging on the flowers of three plant species in a suburban green belt including one native (Arthropodium strictum) and two non-native (Arctotheca calendula and Taraxacum officinale) plant species. We then collected native halictid bees foraging on each of the three plant species and conducted controlled binary tests to determine their preferences for the flowers of native or non-native plant species. In the field counts, halictid bees visited the native plant significantly more than the non-native species. However, in the behavioural assays when comparing A. strictum vs. A. calendula, Lasioglossum (Chilalictus) lanarium (Family: Halictidae), bees significantly preferred the non-native species, regardless of their foraging history. When comparing A. strictum vs. T. officinale, bees only showed a preference for the non-native flower when it had been collected foraging on the flowers of that plant species immediately prior to the experiment; otherwise, they showed no flower preference. Our results highlight the influence that non-native angiosperms have on native pollinators and we discuss the complexities of the results and the possible reasons for different flower preferences under laboratory and field conditions.