Insect Visitors Research Articles

Exploring the beekeeping potential of Sanguisorba dodecandra Moretti: insect visitation, open pollination efficiency, and volatile profiles of honey and flowers

Exploring the beekeeping potential of Sanguisorba dodecandra Moretti: insect visitation, open pollination efficiency, and volatile profiles of honey and flowers

Biological invasions threaten crops: Alien Himalayan balsam lures and co-opts floral visitors away from cultivated cherry tomatoes

While it has been demonstrated that invasive alien plants pose a threat to co-occurring wild-growing native plants by attracting their pollinators, we know almost nothing about their impact on crop pollination. Alien plants with attractive flowers sometimes occur close to crops and may influence yields when they share the same pollinators and have overlapping flowering periods. We present the results of an experiment on the impact of alien balsam (Impatiens glandulifera) on the pollination of cherry tomato (Solanum lycopersicum var. cerasiforme). We verified whether balsam decreases the number of insect visits to the tomato flowers or, conversely, whether balsam may have a positive influence on the pollination rate of the crop. We also assessed crop production with and without the insect visitors. The study was conducted in southern Poland under garden and greenhouse experimental conditions simulating small-scale cultivation of the crop with a neighbouring patch of the alien plant. The studied plants were exposed to insects visiting flowers of the following variants: only one of the two species was exposed or both species were exposed together. Moreover, two factors that may influence insect visits in flowers were assessed: the chemical composition of the floral scent that attracts insects and floral pathogens infesting pollinators that may deter them. The number of insect visits (mainly Bombus pascuorum) on the tomato flowers decreased significantly when the plants were exposed to the alien balsam. Moreover, alien balsam secreted more flower attractants (mainly fatty acids and their esters) than tomatoes, which could explain more frequent insect visits in balsam flowers. However, the floral pathogens probably had a negligible impact on the number of insect visits to the flowers of the two plants. The level of infestation on both studied species was relatively low (I. glandulifera: 5.1% of all pathogen colonies grown in a laboratory, S. lycopersicum var. cerasiforme: 4.2% and 2.6% of all colonies in the garden and greenhouse, respectively) and we found no pathogens known to infect pollinators. It should be noted, however, that some of these pathogens (e.g. Botrytis cinerea, Fusarium oxysporum and Sclerotinia sclerotiorum) are known to cause severe diseases in many crops. Our results revealed that the presence of attractive invasive alien species near small-scale cultivations may negatively affect crop pollination, resulting in smaller fruit size and irregular shape. The impact of such alien species on crop production and the agricultural economy on a large scale requires further study.

Phenology and Breeding Mechanisms of Calamus lobbianus Becc. and Calamus pygmaeus Becc.

The floral biology of Calamus is relatively unknown except for several species. In this study, Calamus lobbianus and Calamus pygmaeus were selected to represent the non-climbing rattan of the Sundaland's flagellate group. Observations on phenology, floral rewards and floral visitors as well as experiments on the breeding mechanism and operational sex ratio were performed for both species. For both species, anthesis started in the early morning for pistillate and staminate plants, ended by late noon (staminate plants) but lasted till the next day in pistillate plants for both species. Although both species appeared to be aseasonal in flowering, C. lobbianus exhibited a male-biased population while C. pygmaeus did not exhibit any sex bias. Nectar was observed to be extruded from the base of the petals of C. lobbianus of the staminate flowers and sterile staminate flowers of the pistillate plants. The concentration and volume of the nectar of the staminate flower and sterile staminate flower of C. lobbianus peaked at c. 11% and 9 μL around 1100 (Day 1) and c. 13% and 8 μL around 0930 (Day 1), respectively, but only appeared as a layer of glistening exudate in C. pygmaeus. Floral scent was not detected in any of the inflorescences of both species. Several insect visitors were observed to be the primary visitors of both Calamus species which include two species of Tetragonula, a species of Liostenogaster sp., and Stenodyneriellus sp. Experiments on breeding mechanism of C. lobbianus and C. pygmaeus indicate that both species are most likely apomictic. C. pygmaeus is capable of vegetative propagation through the rooting at the tip of inflorescence.

Multi-method approach to assessing the floral-visiting insect assemblage of rare, abophilous plant Baccharis vanessae in Southern California.

Insects are the major pollination vectors for angiosperms, and insects native to a given habitat can play an irreplaceable ecological role in food webs and plant reproduction. With precipitous declines in insect species over the last decades, it is urgent to document insect assemblages in native plant communities to support conservation efforts. Identifying pollinators and their pollination activity is challenging; however, emerging technological methods are providing new monitoring capabilities. In this study, we compare the accuracy of two different methods of monitoring to assess the flower-visiting insect assemblage and likely pollinators of Encinitas baccharis (Baccharis vanessae): focal observations and video recordings from camera traps. B. vanessae is a rare, endemic species found in Coastal Sage Scrub communities in San Diego County. This federally listed species is threatened by habitat loss and fragmentation, which may also be affecting the availability of its insect pollinators. Results indicate that B. vanessae supports and is supported by a variety of flower-visiting insect groups. The diversity of insect visitors at male and female plants were similar across all diversity measurements. The insect vectors identified were as expected given B. vanessae pollination syndrome. This syndrome also aligns with wind as a pollination vector, providing evidence of ambophily. While focal observations underreported insect activity by approximately half, the proportions of common diurnal visitors were similar with both methods. Camera traps were unable to provide sufficient detail to discern visually similar groups, but were able to record nocturnal insect activity, which was dominated by moths (Lepidoptera, 82%). While collection protocol in this study did not record the time an insect spent interacting with a flower, we anecdotally observed moths spent notably longer periods in contact with flowers than most diurnal insects. This study has implications for effective monitoring and conservation of endangered plant species and their affiliated pollinators.

Flowering phenology patterns promotes pollination facilitation in coexisting Anthurium species from a mountain forest in Colombia

AbstractCo-flowering congeneric plant species may either experience competition for the services of shared pollinators or facilitation when together, they attract a higher number and diversity of pollinators. In this study, we evaluate whether temporal segregation in flowering time and temporal partition of shared pollinators operate among sympatric Anthurium species as mechanisms to reduce competition to attract potential pollinators. We investigated flowering phenology, the intra-e interspecific synchrony, and the composition of the flower visitor community of seven coexisting Anthurium species biweekly for a whole year in Native and Pine forests. We also analyzed the structure of Anthurium -flower visitor networks and the functional role of species. Flowering was continuous thorough the year for most Anthurium species, but their flowering peaks were segregated significantly in time. Although the flowering periods of these species overlapped, flower visitor communities were very dissimilar among Anthurium species, sharing only a tiny fraction of insects that function as connectors among species in the network. The partition of potential pollinators in a fine temporal scale occurred through the rewiring of shared flower visitors to the most abundant flowering Anthurium species. On the other hand, a high number of inflorescences attracted larger abundance and richness of insect visitors. Facilitation occurred almost throughout the year, while competition occurred during the flowering peak, where a particular species was the best competitor increasing the constancy of pollinators. This study highlights the role of facilitation and competition as mechanisms that together shape the use of potential pollinator resources between sympatric congeneric plant species.

The Insects Visitor on Wild Israeli Grass Flowers (Asystasia gangetica (L.) T. Anderson)

Insects are invertebrate fauna that are important in various ecosystems and have high diversity and adaptability to various habitats. Insect diversity plays an important role (pollinator, pest control, or natural enemy) in several sectors, such as agriculture, ecology, human health, and natural resources. Apart from their beneficial role, the presence of insects can also be detrimental to humans; for example, insects can cause damage to agricultural products. Therefore, this research aimed to determine the diversity and role of insect visitors to the flowers of the Israeli grass plant (Asystasia gangetica). The research was carried out using a scan sampling survey method around community settlements, especially locations that various wild plants still cover. The research results showed that ten species and 255 individual insects visited Israeli grass flowers, which were divided into five orders, namely Lepidoptera, Coleoptera, Hemiptera, Diptera, and Hymenoptera. The order Lepidoptera is a flower-visiting insect species with the highest abundance and is a pollinator. Flowering plants that grow wild, such as Israel grass, benefit society indirectly by being used as traditional medicine. However, they also positively impact the diversity of flower-visiting insects. The presence of flower-visiting insects that work around grass indirectly has the potential to conserve beneficial grass plants but is underestimated by the community.

Pollination efficiency of important insect visitors on pomegranate (Punica granatum) under mid hill conditions of Himachal Pradesh

Insect pollinators are found to be highly significant in enhancing the quality fruit production and productivity. The experiment was conducted during April–May 2020 and 2021 at Dr Y. S. Parmar University of Horticulture and Forestry, Nauni, Solan, Himachal Pradesh to determine the pollination indices of significant insect pollinators visiting pomegranate (Punica granatum L.). The data on pooled basis from two years revealed that Bombus haemorrhoidalis visited most number of flowers during the day (4.96 flowers/min) followed by Apis mellifera (4.24), Apis cerana (3.95), Apis dorsata (3.76) and Episyrphus balteatus (3.09). The time spent on each flower was maximum by A. cerana (17.10 sec/flower) followed by E. balteatus (17.04 sec), A. dorsata (14.20 sec), A. mellifera (13.07 sec) and haemorrhoidalis (5.36 sec) irrespective of different day hours. A. mellifera (5.43 bees/m2/2 min) activity was maximum followed by A. cerana (5.06), E. balteatus (2.91 visitors/m2/2 min), B. haemorrhoidalis (1.72) and A. dorsata (1.37). Data on loose pollen grains for the two years revealed that A. dorsata adhered maximum number of loose pollen grains (357.00 thousand) followed by B. haemorrhoidalis (283.00 thousand), A. mellifera (98.00 thousand), cerana (41.00 thousand) and solitary bees (28.00 thousand). A. mellifera scored highest pollination index and A. dorsata scored least pollination index. A. mellifera, A. cerana and B. haemorrhoidalis are the primary pollinators that increase pomegranate pollination efficiency whereas A. dorsata, E. baltaeatus and solitary bees are supplementary insects improving pollination in various crops including pomegranate. A. mellifera, A. cerana, B. haemorrhoidalis and A. dorsata were main foragers of pomegranate flowers ensuring effective and efficient pollination.

Wild native insects are efficient pollinators of mangoes in the Northern Territory of Australia

Mango is an economically important fruit crop in tropical regions, including parts of Australia. However, the contribution of native flower visitors to mango pollination and fruit set is currently understudied. We studied cv. Kensington Pride (KP) in the Northern Territory (NT) of Australia to assess the overall contribution of insect pollinators to fruit set through pollinator exclusion treatments – open pollination, total pollinator exclusion and large pollinator exclusion (>5 mm). We also compared diurnal patterns in insect visitation with mango phenology and determined the pollination effectiveness and efficiency of flower visitors based on visitation rates, foraging behaviour and pollen deposition. At 45 days after the first pollinator survey, the number of fruits per panicle in open and large pollinator exclusion treatments was not significantly different from one another, despite large pollinator exclusion panicles receiving less than half of the number of insect visitations. Furthermore, open and large pollinator exclusion treatments had 28- and 30-times higher numbers of fruits per panicle than the total pollinator exclusion treatment, respectively, showing the importance of insect pollination. The native stingless bee Tetragonula mellipes was the most frequent visitor (7906 visits, 62.7 %), followed by a hover fly Mesembrius bengalensis (2404 visits, 19.1 %). Tetragonula mellipes had the highest mango pollen loads on their bodies and deposited more pollen grains on stigmas per visit than other flower visitors, and contributed 75.5 % to the mango pollination services, about 4.5 times more than the next most important pollinator (M. bengalensis: 16.8 %). Our results suggest that T. mellipes efficiently pollinate mango flowers in the NT when wild colonies are abundant in the native vegetation adjacent to the crop. Placing T. mellipes hives in the centre of larger mango orchards may increase pollination services and potentially farm productivity by ensuring good pollination towards the centre of orchard blocks.

Pollination Biology and Life History Traits of the Rare Las Vegas Bear Poppy (Arctomecon californica).

Arctomecon californica, the Las Vegas bear poppy, is a rare plant found only in the eastern Mojave Desert of North America. Because of recent declines in the populations of this endemic plant, conservationists are currently seeking protection for A. californica under the US Endangered Species Act. In this study, we investigated the natural history of A. californica and documented insect visitors potentially pollinating A. californica in Clark County, Nevada. We find that the populations of A. californica fluctuate from year to year, with many populations declining by over 90% from 2021 to 2022. The pollinator communities of A. californica also vary from year to year. In some years, specialist bees in the genus Perdita make up the majority of pollinators, while in other years, generalist bees like Apis mellifera and Hylaeus dominate. Furthermore, we confirm what previous work has suggested, that A. californica requires pollinators to set seed, yet not all insect visitors are good pollinators. This work provides useful natural history information about the Las Vegas bear poppy, which will be informative to conservationists designing strategies to protect this imperiled species.

Intensive ground cover management and landscape simplification affect community-wide floral visitor-plant interactions in olive groves

Plant-pollinator interaction networks can provide insights about the impacts of agricultural practices on biodiversity. However, studies on the agricultural impact on these networks most often focus on specific pollinator guilds (i.e., wild bees), hindering our understanding of the effects at the entire insect visitor community level. Here, we evaluated the impact of intensive agriculture and the moderation effects of landscape context on the topology of community-wide plant-visitor interaction networks (381 insect species). We also compared the responses of wild bee-based networks and community-wide plant-floral visitor networks to agricultural intensification to examine whether the former can be a good proxy of the latter. To this aim, we sampled plant-pollinator interaction networks in 24 paired olive farms with contrasting herb cover management (low-intensity management, where ground herb cover is not removed during the flowering season, and intensive management, with herbs persistently removed by herbicides and/or recurrent tillage) across a gradient of landscape complexity in Andalusia (Spain). Results show that the topology of whole floral visitor interaction networks was affected by the herb cover management and the landscape simplification. Furthermore, we found that the effects of the herb cover management were often moderated through the interaction with the landscape context at both floral stand and landscape scale. However, the landscape scale at which these interaction effects occurred varied with the network metric. Non-bee floral visitors were fundamentally redundant for the network topology. We concluded that the implementation of low-intensity management of ground covers in olive groves, together with the enhancement of the flower stands at the local level (e.g., floral strips) and the maintenance and/or restoration of semi-natural habitats at the large landscape scale, would be beneficial to the preservation of healthy and robust floral visitor communities. Our study further supports that wild-bee based interaction networks may adequately reflect the response of the entire networks of plant-floral visitor, at least in this study system.

Differential impacts of land‐use change on multiple components of common milkweed (Asclepias syriaca) pollination success

AbstractLand‐use change is one the greatest threats to biodiversity and is projected to increase in magnitude in the coming years, stressing the importance of better understanding how land‐use change may affect vital ecosystem services, such as pollination. Past studies on the impact of land‐use change have largely focused on only one aspect of the pollination process (e.g., pollinator composition, pollinator visitation, and pollen transfer), potentially misrepresenting the full complexity of land‐use effects on pollination services. Evaluating the impacts across multiple components of the pollination process can also help pinpoint the underlying mechanisms driving land‐use change effects. This study evaluates how land‐use change affects multiple aspects of the pollination process in common milkweed populations, including pollinator community composition, pollinator visitation rate, pollen removal, and pollen deposition. Overall, land‐use change altered floral visitor composition, with small bees having a larger presence in developed areas. Insect visitation rate and pollen removal were also higher in more developed areas, perhaps suggesting a positive impact of land‐use change. However, pollen deposition did not differ between developed and undeveloped sites. Our findings highlight the complexity evaluating land‐use change effects on pollination, as these likely depend on the specific aspect of pollination evaluated and on the of the intensity of disturbance. Our study stresses the importance of evaluating multiple components of the pollination process in order to fully understand overall effects and mechanisms underlying land‐use change effects on this vital ecosystem service.

Reproductive biology of Senna spectabilis (DC.) H.S.Irwin & Barneby (Fabaceae) - an invasive tree species in the tropical forests of the Western Ghats, India

Senna spectabilis (DC.) H.S.Irwin & Barneby is an invasive tree species native to tropical America and is commonly found in the forest areas of Wayanad Wildlife Sanctuary. Its aggressive growth rate and ability to quickly cover up open and degraded lands in forest ecosystems make it challenging to control its spread. Reproductive studies of S. spectabilis and its pollen-ovule ratio indicate this species is cross-pollinating. The species is self-compatible, owing to the simultaneous occurrence of xenogamy, geitonogamy and autogamy. This reproductive strategy helps the taxon to colonise degraded areas and invade the forest ecosystem. The anthesis is diurnal and sometimes asynchronous. Peak insect visitors were observed from 0900 h to 1230 h, with the major visitor being Tetragonula iridipennis. Xylocopa violaceae was also a regular visitor along with resident Formicidae members, such as Oecophylla smaragdina and Myrmicaria brunnae. They feed on the floral parts, like tender petals and sepals. The reproductive syndrome of this plant favours maximum fertilization.

Further Studies in the Pollination of some Indian Asclepiads

Mechanism of pollination, attachment of pollinia with various body parts of insect visitors of order hymenoptera and lepidoptera and their role in pollination of a few asclepiads, viz. Asclepias curassavica L., Calotropis procera (Ait.) R. Br, Wattakaka volubilis (L.) Stapf. Leptadenia reticulata R.Br., Sarcostemma (Oxystelma) secamone (L.) Bennett. and Pergularia daemia (Forsk) Blatt. has been discussed. However, autophily by insu germination of Pollinia in three genera, viz., Hemidesmus indicus Br. Gymnema sylvestre Br. and Tylophora hirsuta (Burm f.) Merr. has been reported for the first time in family Asclepiadaceae.

Reproductive biology of Capparis decidua (Kair): A potential underutilized multipurpose plant of arid and semi arid region

Foliation and flowering of Capparis decidua occurs three times a year i.e. from January to November months. Flowers are bracteate, pedicellate, complete, hermaphrodite, zygomorphic, hypogynous with slender pedicel, usually light red, scarlet red and yellow in colour. Anthesis was maximum between 4.00 p.m. to 8.00 PM and 6.00 to 10.00 AM. Pollen grains are prolate, tricolporate, trilobed, with costae, colpal membrane sparsely granulated. Anther dehiscence takes place after 20–30 minutes of anthesis at 6.00 to 8.00 PM by the time the flowers starts antehsizing, the anthers are almost mature. The viability of pollen grains ranges from 38–52%, and starts decreasing in the stored pollen. The percentage fruit set decreases with the collection time of the pollen grains and plant type. According to visual observation stigmatic surface change in the appearance i.e. green coloured stigma was considered receptive while dull and brown was accounted non-receptive. Pollen germination in-vivo showed 80 per cent stigma receptive and 90 percent of fruit set in the flowers pollinated on the time of anthesis. Pollen grains per anther were ranging from 331–369, fully developed and mature anthers differing significantly among the plant types. The mean number of pollen grains per ovule was 4309 thus the pollen-ovule ratio was 431:1. There is 17–23% fruit set observed under self pollination (autogamy and geitonogamy) and 52–72% as a result of cross pollination. The cross pollinated nature of C. decidua is due to entomophilic nature of flowers, insect visitors which play the main role of pollination are from Apidae and Papilionidae.

Analyses of the sexual reproductive traits for conservation and sustainable utilization of Dactylorhiza hatagirea – A critically endangered medicinal orchid of North-western Himalaya

To undertake scientifically appropriate management and conservation practices, understanding the reproductive biology of endemic and threatened species is critical. Dactylorhiza hatagirea is an important medicinal plant whose reproductive strategies and adaptive evolution mechanisms are still not fully clear. The present study was conducted in the North-western Himalaya of India to understand the reproductive biology, breeding system and pollination ecology of D. hatagirea; an endemic and critically endangered orchid. It is a perennial herb that grows along the altitudinal gradients of 2100–3107 m.a.s.l. and overcomes harsh winters through underground perrenating tubers. The flowering commences from May to July and the flowers are completely zygomorphic with male and female reproductive organs fused to constitute gynostemium. Analysis of variance (ANOVA) show significant statistical difference (p < 0.05) between the floral traits for most of the characters. Each flower bears two dark green colored pollinaria with an average of 212.14 ± 14.4 pollinia. Pollen occur as tetrads and polyads in massulae and their viability was greater than 95 ± 4.2 %. Stigma receptivity was confirmed on the day of anthesis and reaches its peak on 5–6th day. Cruden outcrossing index (5), asynchronous anthesis, conspicuous inflorescences, nectaries, presence of rostellum and herkogamy points towards outcrossing nature while pollen ovule ratio (1.27 ± 0.4) and the greater value of self-incompatibility (0.9) reflect that plants are potent cross-breeders. Pollination treatments significantly impacted seed set in D. hatagirea (one-way ANOVA; F = 23.14; p = 0.001) with an average seed set of 92.75 % ± 0.95 for manual xenogamy (p < 0.01), 89.5 % ± 2.38 for geitonogamy (p < 0.01) and 17 % ± 2.2 for bagged inflorescences (p<0.05). Pollination syndrome is exclusively entomophilly. Insignificant difference was reported in the timining for the insect visitation to flowers (calculated value = 3.4; critical value = 5.1; p < 0.01), however different environmental factors created a significant impact on the frequency of insect visitation (calculated value = 9.7; critical value = 4.3; p < 0.01). Apis cerana, Apis mellifera and Bombus asiaticus show highest pollination indices (p < 0.01) and were characterized as dominant pollinators. This study provides a detailed explanation and substantial understanding regarding operative reproductive mechanism of this threatened medicinal plant and can be used by conservation biologists to develop holistic and effective conservation strategies and address the unique challenges that this threatened species face in the wild.

Generalist southern African temperate forest canopy tree species have distinct pollinator communities partially predicted by floral traits

AbstractForest canopies provide important resources for insect communities via flowers. Yet, pollination systems of tall forest trees are poorly studied, resulting from the difficulties in observing pollinator activity at the canopy level and great temporal variation in flower production. In temperate forest canopies of the southern hemisphere, small, whitish and generalist flowers seem to dominate. Here, we observed insect flower visitors, at the canopy level, to four southern Afrotemperate forest tree species bearing small, white to green flowers in a large, indigenous forest. Additionally, we quantified flower traits and collected pollen from representative insect visitors. A total of 105 insect species, from 48 families and 7 orders, were observed visiting flowers. In terms of total flower visits, the generalist Cape honey bee (Apis mellifera capensis) made up ca. 57% of all flower visits. A third of the total observation time covered crepuscular to nocturnal flower visits; yet only 12.68% of total visits took place during this time. Interestingly, despite both trees and insects being largely generalist in their interactions with one another (supported by the presence of conspecific and heterospecific pollen on most flower visitors), some insect species showed strong preferences for specific species of tree, driving dissimilar, interspecific assemblages of flower visitors. The pollinator community disparity may be explained through the unique and dissimilar floral traits for each tree species, both in flower size and in petal reflectance. We conclude that within generalist pollination systems, distinct and non‐random mutualisms can develop between different species of plants and a diverse suite of pollinators, and that floral traits could partially predict such interactions.

Wild insects and honey bees are equally important to crop yields in a global analysis

AbstractAimMost of the world's food crops are dependent on pollinators. However, there is a great deal of uncertainty in the strength of this relationship, especially regarding the relative contributions of the honey bee (often a managed species) and wild insects to crop yields on a global scale. Previous data syntheses have likewise reached differing conclusions on whether pollinator species diversity, or only the number of pollinator visits to flowers, is important to crop yield. This study quantifies the current state of these relationships and links to a dynamic version of our analyses that updates automatically as studies become available.LocationGlobal.Time PeriodPresent.Taxa studiedInsect pollinators of global crops.MethodsUsing a newly created database of 93 crop pollination studies across six continents that roughly triples the number of studies previously available, we analysed the relationship between insect visit rates, pollinator diversity, and crop yields in a series of mixed‐effects models.ResultsWe found that honey bees and wild insects contribute roughly equal amounts to crop yields worldwide, having similar average flower visitation rates and producing similar increases in yield per visit. We also found that pollinator species diversity was positively associated with increased crop yields even when total visits from all species are accounted for, though it was less explanatory than the total number of visits itself.Main conclusionsOur analysis suggests a middle ground where honey bees are not responsible for the vast majority of crop pollination as has often been assumed in the agricultural literature, and likewise wild insects are not vastly more important than honey bees, as recent global analyses have reported. We also conclude that while pollinator diversity is less important than the number of pollinator visits, these typically involve many species, underscoring the importance of conserving a diversity of wild pollinators.

Hedgerow Gardens Provide Floral Resources for Diverse Insect Visitors to Avocado Fowers in Southern California

Hedgerow Gardens Provide Floral Resources for Diverse Insect Visitors to Avocado Fowers in Southern California

Hedgerow Gardens Provide Floral Resources for Diverse Insect Visitors to Avocado Flowers in Southern California

Hedgerow Gardens Provide Floral Resources for Diverse Insect Visitors to Avocado Flowers in Southern California

Spillover effects from invasive Acacia alter the plant-pollinator networks and seed production of native plants.

Invasive flowering plants can disrupt plant-pollinator networks. This is well documented where invasives occur amongst native plants; however, the potential for 'spillover' effects of invasives that form stands in adjacent habitats are less well understood. Here we quantify the impact of two invasive Australian species, Acacia saligna and Acacia longifolia, on the plant-pollinator networks in fynbos habitats in South Africa. We compared networks from replicate 1 ha plots of native vegetation (n = 21) that were subjected to three treatments: (1) at least 400 m from flowering Acacia; (2) adjacent to flowering Acacia, or (3) adjacent to flowering Acacia where all Acacia flowers were manually removed. We found that native flowers adjacent to stands of flowering Acacia received significantly more insect visits, especially from beetles and Apis mellifera capensis, and that visitation was more generalized. We also recorded visitation to, and the seed set of, three native flowering species and found that two received more insect visits, but produced fewer seeds, when adjacent to flowering Acacia. Our research shows that 'spillover' effects of invasive Acacia can lead to significant changes in visitation and seed production of native co-flowering species in neighbouring habitats-a factor to be considered when managing invaded landscapes.