Flower-visiting Insects Research Articles

Alien plants have greater impact than habitat fragmentation on native insect flower visitation networks

AbstractAimHabitat fragmentation and alien species are among the leading causes of biodiversity loss. In an attempt to reduce the impact of forestry on natural systems, networks of natural corridors and patches of natural habitat are often maintained within the afforested matrix, yet these can be subject to degradation by invasion of non‐native species. Both habitat fragmentation and alien invasive species disrupt the complex interaction networks typical of native communities. This study examines whether an invasive plant and/or the fragmented nature of the forestry landscape influences natural flower visitation networks (FVNs), flower–visitor abundance and richness or flower/visitor species composition.LocationThe species rich and diverse grasslands in the KwaZulu‐Natal Midlands, South Africa is under threat from transformation, particularly by commercial forestry plantations, restricting much of the remaining untransformed grasslands into remnant grassland patches (RGPs). Remaining patches are under additional threat from the invasive Rubus cuneifolius Pursh (bramble). Sites were established in RGPs and in a nearby protected area (PA), with and without brambles present for both areas.ResultsFlower abundance and flower area of native plant species were greater within RGP than in PA, but only in the absence of R. cuneifolius. Flower–visitor assemblages differed between invaded and uninvaded sites and also differed between PA and RGP sites. Both areas lost specialist flower–visitor species in the presence of brambles. Network modularity was greatly reduced by the presence of bramble, indicating a reduction in complexity and organization. The structure of FVNs was otherwise unaffected by presence of bramble or being located in RGPs or the PA.Main conclusionsThe RPGs contribute to regional biodiversity conservation through additional compositional diversity and intact FVNs. Rubus cuneifolius reduces ecological complexity of both RGPs and PAs, however, and its removal must be prioritized to conserve FVNs.

Exotic plants growing in crop field margins provide little support to mango crop flower visitors

Introduced plant species integrate into native trophic networks, often disrupting flower-visitation patterns. Although non-native invasive plants frequently occur in disturbed natural vegetation bordering crop fields, their impact on crop pollination has not been studied. We investigated whether an invasive plant (Lantana camara) influences flower visitation to mango (Mangifera indica), a pollinator-dependent crop, and whether the invasive supports mango pollinators when mango is not flowering. We surveyed insect flower-visitation in mango orchards bordering natural vegetation and within adjacent natural vegetation, with and without L. camara present, before, during and after mango flowering. We used these data to calculate the indirect effect of L. camara on mango through shared flower visitors before, during and after mango flowering, and the effects of the invasive on crop productivity. Lantana camara had a positive effect on mango flower visitation at low to medium mango flower density, but not at high mango flower densities. Although L. camara and mango shared flower visitor species, the frequency with which these flower visitor species visited the crop and the invasive differed markedly before, during and after mango flowering. Furthermore, the potential indirect effect of L. camara on mango via shared visitors was greatest when mango was flowering, but significantly lower before and after mango flowering, suggesting that the invasive is unimportant in the diet of mango flower visitors when the crop is not flowering. Contrary to findings in previous studies using native species in mango fields, there was a trend (not significant) for lower mango fruit production in fields with L. camara. This suggests that Lantana does not contribute to an increase in successful pollination of mango. Although our focal alien invasive plant species facilitated flower visitation of crops, it had no effect on mango production, and provided little support to mango flower visitor species that live longer than the crop’s flowering period. Given that L. camara is detrimental to grazing and was not associated with increased mango production, the removal of this invasive is advisable.

Importance of birds versus insects as pollinators of the African shrub Syncolostemon densiflorus (Lamiaceae)

Flowers visited by a broad assemblage of animals may nevertheless be considered to have a specialized pollination system if pollen deposition is effected mainly by a subset of these visitors. The importance of a particular animal group for pollination derives mainly from the relative rate of floral visitation and per-visit effectiveness for pollen deposition. We assessed the relative importance of birds and insects for pollination of the African shrub Syncolostemon densiflorus (Lamiaceae). Flower visitors were observed to evaluate their visitation rates. Virgin flowers were exposed to single visits by nine animal visitor groups to evaluate their effectiveness at depositing pollen on stigmas. We selectively excluded birds and larger insects from flowers to assess the contribution of smaller visitors to pollen deposition and seed set. Sunbirds and insects visited flowers at a similar frequency, but on a per-visit basis, sunbirds deposited more pollen on stigmas than did any of the insect groups, including honeybees, long-proboscid flies, butterflies and day-flying hawkmoths. Selective exclusion of birds and larger insects resulted in a large decline in pollen deposition on stigmas and seed production. These results show that S. densiflorus is pollinated mainly by sunbirds, despite its attraction of a broad assemblage of insect flower visitors. These findings highlight the importance of per-visit pollination effectiveness and selective exclusion for understanding the ecological importance of different flower visitors.

Identifying species at coextinction risk when detection is imperfect: Model evaluation and case study.

Losing a species from a community can cause further extinctions, a process also known as coextinction. The risk of being extirpated with an interaction partner is commonly inferred from a species’ host-breadth, derived from observing interactions between species. But observational data suffers from imperfect detection, making coextinction estimates highly unreliable. To address this issue and to account for data uncertainty, we fit a hierarchical N-mixture model to individual-level interaction data from a mutualistic network. We predict (1) with how many interaction partners each species interacts (to indicate their coextinction risk) and (2) how completely the community was sampled. We fit the model to simulated interactions to investigate how variation in sampling effort, interaction probability, and animal abundances influence model accuracy and apply it to an empirical dataset of flowering plants and their insect visitors. The model performed well in predicting the number of interaction partners for scenarios with high abundances, but indicated high parameter uncertainty for networks with many rare species. Yet, model predictions were generally closer to the true value than the observations. Our mutualistic plant-insect community most closely resembled the scenario of high interaction rates with low abundances. Median estimates of interaction partners were frequently much higher than the empirical data indicate, but uncertainty was high. Our analysis suggested that we only detected 14-59% of the flower-visiting insect species, indicating that our study design, which is common for pollinator studies, was inadequate to detect many species. Imperfect detection strongly affects the inferences from observed interaction networks and hence, host specificity, specialisation estimates and network metrics from observational data may be highly misleading for assessing a species’ coextinction risks. Our study shows how models can help to estimate coextinction risk, but also indicates the need for better data (i.e., intensified sampling and individual-level observations) to reduce uncertainty.

Alpha and Beta Diversity of Flower-visiting Insects in Different Land Use Types

Alpha and Beta Diversity of Flower-visiting Insects in Different Land Use Types

Contribution of honeybees to soybean yield

Despite the economic importance of soybean [Glycine max (L.) Merr.], knowledge on the contribution of entomological pollination on seed yield is scarce. This study estimates the production of soybean resulting from pollination by honeybees (Apis mellifera L.) in two consecutive growing seasons in Paraná (Argentina). Experiments had two treatments: excluded flower-visiting insects (EV) and non-excluded flower-visiting insects (NEV). The abundance of honeybees was similar in both years, although soybean production differed significantly (P < 0.05) between years. The NEV treatment out-yielded (P < 0.001) the EV treatment by 18% (5224 vs. 4415 kg ha−1) in year 1, which was associated with an increase in the seeds per unit area but not with individual seed weight. In contrast, seed yield (on average 3830 kg ha−1) and seeds per unit area did not differ between treatments in year 2. Individual seed weight was 3–5% (P < 0.05) higher in EV than in NEV in both years. The mechanisms involved in the seed yield increase could be related with pollen sterility in relegated flowers in secondary racemes or in distal locations of primary racemes under favorable conditions, as recorded in year 1. Thus, the action of honeybees carrying pollen from fertile flowers to relegated flowers may have increased the pod and seed set in treatment NEV in year 1.

Interaction between insects and insect-pollinated plants on Miyake Island after a recent volcanic eruption: A comparison between vegetation types

In habitats after natural disturbance, mutualistic interaction between plant and flower-visiting insects is critical for maintenance and recovery of communities. However, the detailed characteristics of the plant-insect interactions that occur after a natural disturbance remain to be identified. We investigated the network structure of these interactions on the oceanic and volcanic island of Miyake, Japan. Large vegetated areas of this island were disturbed by a massive volcanic eruption during 2000. In 2012, we sampled insects visiting the flowering plants along the roadsides bordering six sites in the 3 vegetation types, which represent the island's vegetation after the volcanic disturbance; (1) shrubland colonizing accumulated ash (SL), (2) mature broad-leaved forests with partial damage (BF), and (3) coastal vegetation with partial damage (CV). Network properties, such as specialization, nestedness, and modularity did not differ among the three vegetation categories. We found the same specialized, modular, and anti-nested structures in five networks. The largest variation in insect/plant assemblages was observed between CV and the other vegetation types, but we did not find distinctive variations between SL and BF sites. Our study suggests that network structure is constant in the varying vegetation types, and raises the possibility that this island's mutualistic interactions are robust to volcanic disturbance.

Evolution of Lower Brachyceran Flies (Diptera) and Their Adaptive Radiation with Angiosperms.

The Diptera (true flies) is one of the most species-abundant orders of Insecta, and it is also among the most important flower-visiting insects. Dipteran fossils are abundant in the Mesozoic, especially in the Late Jurassic and Early Cretaceous. Here, we review the fossil record and early evolution of some Mesozoic lower brachyceran flies together with new records in Burmese amber, including Tabanidae, Nemestrinidae, Bombyliidae, Eremochaetidae, and Zhangsolvidae. The fossil records reveal that some flower-visiting groups had diversified during the mid-Cretaceous, consistent with the rise of angiosperms to widespread floristic dominance. These brachyceran groups played an important role in the origin of co-evolutionary relationships with basal angiosperms. Moreover, the rise of angiosperms not only improved the diversity of flower-visiting flies, but also advanced the turnover and evolution of other specialized flies.

Precipitation and the robustness of a plant and flower-visiting insect network in a xeric ecosystem

Complex networks of species interactions are integral to the stability of ecological communities. The responses of these networks to extreme environmental fluctuations are key to understanding the evolution of these networks and their roles in stabilizing ecological communities. From 2008 to 2009 we observed the effects of extreme differences in annual precipitation on a network of plants and flower-visiting insects in a xeric grassland. Significant decreases in plant and insect diversity in the dry year were mirrored by decreases in the number of network nodes and links. However, the relative density of network connections increased in the dry year and other important topological features, such as nestedness and modularity, were largely unchanged. The resilience of the network to node (plants or insect species) loss was high in both years. Though bees tend to dominate pollination communities in drier climes, we did not observe a shift in the relative richness of bee species in the dry year. Our results indicate that well-linked, drought-resistant plants are important to community resilience during ecologically challenging periods and that networks of plants and flowering-visiting insects may be robust to extreme climatic change, at least over short periods, as long as those critical, resilient hubs are protected.

Cotton Flower-visiting Insects in Small-scale Farm Fields in Mwachisompola, Zambia

Global declines in wild and managed pollinator species have increased the need to evaluate the current status of these populations and understand their needs for sustainability. Farming systems can be a useful place to examine the presence and activity of flower-visiting insects, because the blooming period of the crop provides a predictable floral resource which serves as an attractant to some species. The density and species richness of cotton flower-visiting insects were measured in five conservation and five conventional cotton fields in Mwachisompola, Zambia. Between the two farm types, density and species richness were not significantly different; however, only 33% of the total observed species were found within both farm systems. We found a significant negative relationship between species richness and field size regardless of farm type. Our results suggest that cotton fields attract both pollinator and predatory flower-visiting insects regardless of management, however more work is needed to better understand the effects of field size and surrounding natural areas.

Flower-visiting insects observed on the critically endangered alpine plant species Callianthemum kernerianum Freyn ex A. Kerner (Ranunculaceae)

In the present paper we provide the first contribution to the knowledge of the flower-visiting insect assemblages of the alpine plant species Callianthemum kernerianum Freyn ex A. Kerner (Ranunculaceae). This focal plant species was selected since it is a steno-endemic and critically endangered species belonging to the IUCN red-list. Fifteen taxa were recorded, among which very few are true pollinators, whereas all the others can be considered only indirect pollinators. The peculiar phenology of the plant and the harsh habitat conditions in which it grows probably affect the richness and abundance of flower-visiting insects as well as of true pollinators. This could be the reason for this plant to be a self-compatible species.

Oilseed rape (Brassica napus) as a resource for farmland insect pollinators: quantifying floral traits in conventional varieties and breeding systems.

Oilseed rape (OSR; Brassica napus L.) is a major crop in temperate regions and provides an important source of nutrition to many of the yield‐enhancing insect flower visitors that consume floral nectar. The manipulation of mechanisms that control various crop plant traits for the benefit of pollinators has been suggested in the bid to increase food security, but little is known about inherent floral trait expression in contemporary OSR varieties or the breeding systems used in OSR breeding programmes. We studied a range of floral traits in glasshouse‐grown, certified conventional varieties of winter OSR to test for variation among and within breeding systems. We measured 24‐h nectar secretion rate, amount, concentration and ratio of nectar sugars per flower, and sizes and number of flowers produced per plant from 24 varieties of OSR representing open‐pollinated (OP), genic male sterility (GMS) hybrid and cytoplasmic male sterility (CMS) hybrid breeding systems. Sugar concentration was consistent among and within the breeding systems; however, GMS hybrids produced more nectar and more sugar per flower than CMS hybrid or OP varieties. With the exception of ratio of fructose/glucose in OP varieties, we found that nectar traits were consistent within all the breeding systems. When scaled, GMS hybrids produced 1.73 times more nectar resource per plant than OP varieties. Nectar production and amount of nectar sugar in OSR plants were independent of number and size of flowers. Our data show that floral traits of glasshouse‐grown OSR differed among breeding systems, suggesting that manipulation and enhancement of nectar rewards for insect flower visitors, including pollinators, could be included in future OSR breeding programmes.

Most ornamental plants on sale in garden centres are unattractive to flower-visiting insects.

BackgroundGardeners and park managers seeking to support biodiversity in urban areas often plant ornamentals attractive to flower-visiting insects. There is a huge diversity of garden plant varieties, and some recommendations are available as to which are attractive to insects. However, these are largely not based on rigorous empirical data. An important factor in consumer choice is the range of varieties available for purchase. In the UK, garden centres are a key link in the supply chain between growers and private gardens. This study is the first to determine the proportions of flowering ornamentals being sold that are attractive to flower-visiting insects.MethodsWe surveyed six garden centres in Sussex, UK, each over two days in 2015, by making 12 counts of insects visiting patches of each ornamental plant on display for sale that was in bloom. To provide a consistent baseline among different locations, we brought with us and surveyed marjoram (Origanum vulgare) plants in pots, which are known to be attractive to a wide range of flower-visiting insects. The attractiveness of plant varieties to insects was then expressed in two ways: the absolute number and relative to that on marjoram (‘marjoram score’), both per unit area of plant cover. In addition, we noted whether each variety was recommended as pollinator-friendly either via a symbol on the label, or by being included in the Royal Horticultural Society’s ‘Perfect for Pollinators’ list. Furthermore, we compared the attractiveness of plants that are typically grown for more than one year versus only one year.ResultsWe surveyed 59–74 plant varieties in bloom across the six garden centres. In each garden centre, the distributions of variety attractiveness were highly skewed to the right, with most varieties being relatively unattractive, and few varieties highly attractive to flower-visiting insects. The median attractiveness of varieties with a recommendation was 4.2× higher than that of varieties without. But, due to the large variation there was a substantial number of both poor varieties that had a recommendation and good varieties that did not. Median attractiveness of multi-year plants was 1.6× that of single-year plants, with a similar overlap in distributions.DiscussionOur study demonstrates the practicality of carrying out plant surveys in garden centres. Garden centres display large numbers of varieties for sale, most of which are in bloom. Furthermore, data gathered in garden centres appear to correlate well with data gathered in two previous studies in Sussex for plants established in gardens. Although it is unclear whether the varieties being sold in garden centres are a fair representation of varieties that are actually grown by gardeners, our results suggest that there might be considerable scope for making parks and gardens considerably more insect-friendly through judicious variety choices.

A biodiversity-friendly rotational grazing system enhancing flower-visiting insect assemblages while maintaining animal and grassland productivity

Grazing management is an important tool to preserve insect biodiversity. Although literature has discussed the importance of grazing pressure adjustment to support grassland insect communities for the ecosystem services they provide, little has been published on the economic sustainability of such management adjustments to date. This study compared continuous grazing (CG) to an innovative rotational grazing system (the biodiversity-friendly rotation – BR), where a subplot was excluded from grazing for two months during the main flowering period. The effects of grazing two different species (cattle and sheep) within both systems were also evaluated. The aims were to assess the effects on butterfly, bumblebee, and ground beetle assemblages, along with the impact on herbage mass and animal performance. The BR enhanced both the abundance and species richness of flower-visiting insect assemblages and it was observed that cattle provided better results than sheep grazing. A multivariate redundancy analysis highlighted that most of the flower-visiting species (including almost all the endangered and locally rare species) were favoured by BR-cattle treatment, mainly due to the high percentage of flower cover and sward heterogeneity involved in this treatment. However, grazing system and grazer species did not affect ground beetle species richness or abundance. Moreover, herbage mass and animal performance (live weight and body condition score) were comparable between CG and BR throughout the grazing season. The BR could be a useful management system to enhance grassland flower-visiting insect assemblages whilst meeting farm production objectives, especially in protected environments where insect conservation is a major target.

Multisensory integration in Lepidoptera: Insights into flower-visitor interactions.

As most work on flower foraging focuses on bees, studying Lepidoptera can offer fresh perspectives on how sensory capabilities shape the interaction between flowers and insects. Through a combination of innate preferences and learning, many Lepidoptera persistently visit particular flower species. Butterflies tend to rely on their highly developed sense of colour to locate rewarding flowers, while moths have evolved sophisticated olfactory systems towards the same end. However, these modalities can interact in complex ways; for instance, butterflies' colour preference can shift depending on olfactory context. The mechanisms by which such cross-modal interaction occurs are poorly understood, but the mushroom bodies appear to play a central role. Because of the diversity seen within Lepidoptera in terms of their sensory capabilities and the nature of their relationships with flowers, they represent a fruitful avenue for comparative studies to shed light on the co-evolution of flowers and flower-visiting insects.

Network size, structure and mutualism dependence affect the propensity for plant–pollinator extinction cascades

Summary Pollinator network structure arising from the extent and strength of interspecific mutualistic interactions can promote species persistence and community robustness. However, environmental change may re‐organise network structure limiting capacity to absorb or resist shocks and increasing species extinctions. We investigated if habitat disturbance and the level of mutualism dependence between species affected the robustness of insect–flower visitation networks Following a recently developed Stochastic Co‐extinction Model (SCM), we ran simulations to produce the number of extinction episodes (cascade degree), which we correlated with network structure in undisturbed and disturbed habitat. We also explicitly modelled whether a species’ intrinsic dependence on mutualism affected the propensity for extinction cascades in the network. Habitat disturbance generated a gradient in network structure with those from disturbed sites being less connected, but more speciose and so larger. Controlling for network size (z‐score standardisation against the null model) revealed that disturbed networks had disproportionately low linkage density, high specialisation, fewer insect visitors per plant species (vulnerability) and lower nestedness (NODF). This network structure gradient driven by disturbance increased and decreased different aspects of robustness to simulated plant extinction. Disturbance decreased the risk that an initial insect extinction would follow a plant species loss. Although, this effect disappeared when network size and connectance were standardised, suggesting the lower connectance of disturbed networks increased robustness to an initial secondary extinction. However, if a secondary extinction occurred then networks from disturbed habitat were more prone to large co‐extinction cascades, likely resulting from a greater chance of extinction in these larger, speciose networks. Conversely, when species mutualism dependency was explicit in the SCM simulations the disturbed networks were disproportionately more robust to very large co‐extinction cascades, potentially caused by non‐random patterns of interaction between species differing in dependence on mutualism. Our results showed disturbance altered the size and the distribution of interspecific interactions in the networks to affect their robustness to co‐extinction cascades. Controlling for effects due to network size and the interspecific variation in demographic dependence on mutualism can improve insight into properties conferring the structural robustness of networks to environmental changes. A lay summary is available for this article.

Impact of land‐use change on flower‐visiting insect communities on an oceanic island

Abstract Land‐use change has profoundly impacted pollinator communities throughout the world. However, the processes through which it acts on pollinator diversity and composition are still poorly understood, especially in highly vulnerable island ecosystems. In this study, we investigated the distribution, abundance, richness and composition of flower‐visiting insects to assess their response to land‐use change in Terceira Island (Azores). Flower‐visiting insects were sampled over 2 years using a standardised protocol along 50 transects across five different habitats corresponding to a land‐use gradient. Insect species were classified as indigenous or exotics. We assessed changes across habitats using multiple diversity indices, species abundance distribution models (SAD) and species composition metrics (β‐diversity), along with plant species composition. We observed that indigenous flower‐visiting insects were dominant, both in abundance and species richness, across the entire land‐use gradient. Species diversity varied only slightly across the gradient. SADs were lognormal in all habitats, with very few truly common and rare flower‐visiting insects and a prevalence of species of intermediate abundance. Species replacement was significantly higher mainly between the two most contrasting habitats (i.e. natural forests and intensive pastures) but was significantly correlated with species replacement of host plant species across the gradient. Our results revealed that the Azorean flower‐visiting insect communities were highly simplified across the entire gradient with little difference between habitats. In the absence of strong exotic competitors, indigenous flower‐visiting insects expand their range and occupy new anthropogenic habitats, also facilitating the expansion of a large number of exotic plant species.

高知県琴ヶ浜の海浜植物群落における訪花昆虫群集の種組成

高知県琴ヶ浜の海浜植物群落における訪花昆虫群集の種組成

Observations of insect visitors to Price’s Potato Bean (Apios priceana, Fabaceae) in North Alabama, USA

Background and aims – Apios priceana is a rare flowering plant that can only be found in parts of the Southeastern United States. Little is known about the reproductive biology of this plant and only a few insect flower visitors have been previously documented. The aim of this study was to further document the insect flower visitors of A. priceana in North Alabama.Methods – Cameras and observers recorded flower visitors during the 2014 blooming season of a large North Alabama population of A. priceana.Key results – Although fifteen different species of insects were documented on flowers of A. priceana, most performed a single or very few visits. Bumble bees ( Bombus spp.), two species of Megachilidae ( Megachile sculpturalis and Megachile campanulae ), and the hummingbird clearwing ( Hemaris thysbe ) were the most common visitors. Interestingly, the giant resin bee, M. sculpturalis, is considered to be an invasive species but in this case may be pollinating a native and Federally threatened plant.Conclusion – Although A. priceana flowers are visited by numerous insects, Bombus spp. and, surprisingly, an invasive species ( Megachile sculpturalis ) are probably the most important pollinators of this plant.

Patterns of diversity of flower-visitor assemblages to the understory Araceae in a tropical mountain forest in Colombia

In the Araceae, pollination biology has been extensively evaluated in several genera mainly in lowland tropical areas. However, the influence of physical factors such as elevation or precipitation on plant/flower-visitor interactions at the community level remains challenging for this plant family, specifically in tropical mountain forests. The aim of this study was to analyze how the species diversity and abundance of flowering Araceae and their flower-visitor assemblages change along an elevation gradient and through time, in response to changes in mean monthly precipitation in a tropical mountain forest located in Jardin, Antioquia, Colombia. Eighteen flowering Araceae species and floral visitors belonging to seven orders were recorded. Flower-visitor diversity decreased with elevation. A trend of increasing flowering Araceae and flower-visitor abundance richness at intermediate levels of precipitation was observed. Diptera were dominant in the lower part and Thysanoptera were dominant in the upper part of the gradient. The pattern of plant species distribution along the elevation and the amount of precipitation influenced the availability of flower resources, and, as a consequence, affected the spatial and temporal composition of flower-visitor assemblages. Local strategies for the conservation of the diversity of insect flower-visitors and their interactions should be focused on the implementation of agricultural practices that reduce the use of pesticides within adjacent commercial plantations and the avoidance of illegal clearings, maintaining unbroken elevational gradients of forest, which is the only way to protect the flowering resources for anthophilous insects. At the same time, continuous forest promotes the maintenance of macro and microclimatic conditions, preserving the stability of insect populations and diversity amongst several functional groups.