Evaluation of Native and Nonnative Ornamentals as Pollinator Plants in Florida: I. Floral Abundance and Insect Visitation

Diverse floral resources impart immense value for pollinating insects of all types. With increasing popularity and demand for modern ornamental hybrids, cultivation by breeders has led to selection for a suite of traits such as extended bloom periods and novel colors and forms deemed attractive to the human eye. Largely understudied is pollinator preference for these new cultivars, as compared with their native congeners. To address this gap in understanding, 10 species of popular herbaceous flowering plants, commonly labeled as pollinator-friendly, were evaluated at two sites in Florida [U.S. Department of Agriculture (USDA) cold hardiness zones 8b and 9a] and across three seasons for their floral abundance and overall attractiveness to different groups of pollinating insects. Each genus, apart from pentas, encompassed a native and nonnative species. Native species included blanket flower (Gaillardia pulchella), lanceleaf coreopsis (Coreopsis lanceolata), pineland lantana (Lantana depressa), and scarlet sage (Salvia coccinea). Nonnative species included Barbican™ yellow-red ring blanket flower (G. aristata ‘Gaiz005’), Bloomify™ rose lantana (L. camara ‘UF-1011-2’), mysty salvia (S. longispicata ×farinacea ‘Balsalmysty’), Lucky Star® dark red pentas (Pentas lanceolata ‘PAS1231189’), ruby glow pentas (P. lanceolata ‘Ruby glow’) and Uptick™ Gold & Bronze coreopsis (Coreopsis × ‘Baluptgonz’). Flower-visiting insects were recorded during five-minute intervals in the morning and categorized into the following morpho-groups: honey bees, large-bodied bees (bumble and carpenter bees), other bees (small to medium-bodied native bees), butterflies/moths, and wasps. Floral abundance and pollinator visitation varied widely by season, location, and species. Of the plant species evaluated, nonnative plants produced nearly twice as many flowers as native plants. About 22,000 floral visitations were observed. The majority of visits were by native, small to medium-bodied bees (55.28%), followed by butterflies and moths (15.4%), large-bodied native bees (11.8%), wasps (10.0%), and honey bees (7.6%). Among plant genera, both native and nonnative coreopsis and blanket flower were most attractive to native, small to medium-bodied bees (e.g., sweat bees, leafcutter bees) with the greatest number of visitations occurring during the early and midmonths of the study (May–August). Across the study, butterflies and moths visited lantana more frequently than all other ornamentals evaluated, whereas pentas were most attractive to wasps. Large-bodied bees visited plants most frequently in May and June, primarily foraging from both native and nonnative salvia. While results from this study showed nominal differences between native and nonnative species in their ability to attract the studied pollinator groups, care should be taken to making similar assessments of other modern plant types.

Plant age at the time of ozone exposure affects flowering patterns, biotic interactions and reproduction of wild mustard

Exposure of plants to environmental stressors can modify their metabolism, interactions with other organisms and reproductive success. Tropospheric ozone is a source of plant stress. We investigated how an acute exposure to ozone at different times of plant development affects reproductive performance, as well as the flowering patterns and the interactions with pollinators and herbivores, of wild mustard plants. The number of open flowers was higher on plants exposed to ozone at earlier ages than on the respective controls, while plants exposed at later ages showed a tendency for decreased number of open flowers. The changes in the number of flowers provided a good explanation for the ozone-induced effects on reproductive performance and on pollinator visitation. Ozone exposure at earlier ages also led to either earlier or extended flowering periods. Moreover, ozone tended to increase herbivore abundance, with responses depending on herbivore taxa and the plant age at the time of ozone exposure. These results suggest that the effects of ozone exposure depend on the developmental stage of the plant, affecting the flowering patterns in different directions, with consequences for pollination and reproduction of annual crops and wild species.

Comparative effects of pollen limitation, floral traits and pollinators on reproductive success of Hedysarum scoparium Fisch. et Mey. in different habitats

Background Reproduction in most flowering plants may be limited because of the decreased visitation or activity of pollinators in fragmented habitats. Hedysarum scoparium Fisch. et Mey. is an arid region shrub with ecological importance. We explored the pollen limitation and seed set of Hedysarum scoparium in fragmented and restored environments, and examined whether pollen limitation is a significant limiting factor for seed set. We also compared floral traits and pollinator visitation between both habitats, and we determined the difference of floral traits and pollinators influenced reproductive success in Hedysarum scoparium. Results Our results indicated that supplementation with pollen significantly increased seed set per flower, which is pollen-limited in this species. Furthermore, there was greater seed set of the hand cross-pollination group in the restored habitat compared to the fragmented environment. More visits by Apis mellifera were recorded in the restored habitats, which may explain the difference in seed production between the fragmented and restored habitats. Conclusions In this study, a positive association between pollinator visitation frequency and open flower number was observed. The findings of this study are important for experimentally quantifying the effects of floral traits and pollinators on plant reproductive success in different habitats.

Small-Scale Habitat Conditions Are More Important Than Site Context for Influencing Pollinator Visitation

The ability of insects to persist in urban greenspace depends on their ability to usefully interact with available plant resources. Greenspace design influences plant–insect interactions by: (1) limiting the plant-species pool available for interaction through plant choice, (2) limiting the insects that are available for interaction through site-occupancy dynamics, and (3) mediating insect preferences based on the context of particular plant–insect interactions through structural barriers, microclimatic changes or competition. We designed an experiment to measure the effect of greenspace design attributes on site occupancy and insect preferences while keeping plant availability constant. Using a set of five functionally distinct flowering plant species (“phytometres”), we used occupancy-detection modelling to test factors affecting probability of visitation for eight groups of pollinating insects (ants, beetles, butterflies, bumblebees, honeybees, small bees, and hoverflies amend other flies) across 102 urban squares in Munich, Germany. We found that the probability of detecting an interaction was low for most functional groups, and situational factors, such as weather or competition from co-occurring flowers, were the primary drivers of visitation. Increasing the proportion of unsealed surfaces and quantity or diversity of flowers on the site had a positive influence on the probability of interaction, and, to a lesser extent, on probability of occupancy. Landscape connectivity and site area were important for only a few groups. Together, our results suggest that small-scale habitat conditions are more important than site context for influencing pollinator visitation. Designers can encourage interaction through contiguous provision of floral resources and unsealed surfaces while limiting internal barriers.

Linking pollinator occurrence in field margins to pollinator visitation to a mass-flowering crop

Uncultivated field margins are important refugia for pollinating insects in agricultural landscapes. However, the spill-over of pollination services from field margins to adjacent crops is poorly understood. This study (i) examined the effects of landscape heterogeneity on pollinator occurrence in permanent field margins and pollinator visitation to adjacent mass-flowering turnip rape (Brassica rapa ssp. oleifera) in boreal agricultural landscapes, and (ii) tested whether pollinator abundance and species richness in field margins predict abundance and species richness of crop visitors. Pollinators visiting the crop were more affected by landscape heterogeneity than pollinators in adjacent margins. Species richness, total abundance, and the abundance of syrphid flies visiting the crop increased with increasing landscape heterogeneity, whereas, in field margins, landscape heterogeneity had little effect on pollinators. In field-dominated homogeneous landscapes, wild pollinators rarely visited the crop even if they occurred in adjacent margins, whereas in heterogeneous landscapes, differences between the two habitats were smaller. Total pollinator abundance and species richness in field margins were poor predictors of pollinator visitation to adjacent crop. However, high abundances of honeybees and bumblebees in margins were related to high numbers of crop visitors from these taxa. Our results suggest that, while uncultivated field margins help pollinators persist in boreal agricultural landscapes, they do not always result in enhanced pollinator visitation to the adjacent crop. More studies quantifying pollination service delivery from semi-natural habitats to crops in different landscape settings will help develop management approaches to support crop pollination.

The influence of floral traits on insect foraging behaviour on medicinal plants in an urban garden of eastern India

Understanding the pollination biology of medicinal plants and their important insect pollinators is necessary for their conservation. The present study explored the complex interactions between pollinator visitation and effect of floral traits on pollinator behaviour on seven medicinal plant species grown in an urban garden in West Bengal, an eastern Indian state. The observations revealed 30 morphospecies of insect flower visitors (Diptera, Lepidoptera and Hymenoptera) that touched floral reproductive parts on the selected plants during visitation. Additionally, it was observed that floral traits (e.g., corolla length and corolla opening diameter) were important predictors of the behaviour of insects when visiting the flowers. Plant–pollinator interactions were analysed using a bipartite network approach which explored the important links between insect and plants in the network revealing the key interactions, and species which are crucial to system maintenance. This piece of work contributes to our ability to understand and maintain a stable medicinal plant–pollinator network which will support efforts to conserve native flora and insects.

Allee Effects Determine Pollinator Services at Local and Geographic Scales

Climatic factors have attracted much attention in the study of species’ distributions, while little is known about the role of biotic interactions. Here, we tested for variation in pollinator service across the distribution of a plant species, and evaluated the driving mechanisms. We monitored insect pollinators using time-lapse cameras in populations of North American Arabidopsis lyrata from the southern to the northern range limit. We spotted 67 pollinating insect taxa, indicating that this plant-pollinator network is a generalist system. Pollinator service increased with latitude. Higher pollinator visitation was correlated with the richness of other flowering plants and with plant census size, which was largest in northern populations. Furthermore, pollinator service reached a maximum at intermediate local flower density. Synthesis: This study indicates that pollination service underlies Allee effects on a local and species’ range scale, and that plant populations at range limits receive only marginal pollination service if they are small.