Attractiveness of single and multiple species flower patches to beneficial insects in agroecosystems

The provision of floral resources for the enhancement of beneficial insect populations has shown promise as a strategy to enhance biological control and pollination in agroecosystems. One approach involves the provision of a single flower species while a second involves the multiple flower species, but the two have never been compared experimentally. Here we examine the influence of single and multiple species flower treatments on the abundance and foraging behaviour of key beneficial insects in two agricultural agroecosystems (broccoli and lucerne crops). The five flower treatments comprised buckwheat only, phacelia only, a simple mixture of buckwheat and phacelia, a complex mixture of buckwheat, phacelia and a commercial seed blend or the existing crop as a control. The abundance of bumble‐bees (Bombus hortorum) and honey bees (Apis mellifera) was highest in the three treatments that contained phacelia, while hoverfly (Melanostoma fasciatum) numbers were high in all four flower treatments. Bumble‐bees and honey bees probed almost exclusively phacelia flowers, even when provided with a choice of other flower species in the simple and complex mixture treatments. In contrast, hoverflies probed the flowers of all plant species in single and multiple species treatments, with no apparent difference in acceptance. However, in mixture treatments, the majority of individual bumble‐bees, honey bees and hoverflies probed the flowers from only one species, despite the presence of alternative flower species. Our results illustrate how an appreciation of insect floral attractiveness can be used to customise the species composition of floral patches to potentially maximise biological control and pollination in targeted agroecosystems.     

Floral visitors and ant scent marks: noticed but not used?

1. Bee behaviour when visiting flowers is mediated by diverse chemical cues and signals, from the flower itself and from previous visitors to the flower. Flowers recently visited by bees and hoverflies may be rejected for a period of time by subsequent bee visitors. 2. Nectar‐thieving ants also commonly visit flowers and could potentially influence the foraging decisions of bees, through the detection of ant trail pheromones or footprint hydrocarbons. 3. Here we demonstrate that, while naÏve bumblebees in laboratory trials are not inherently repelled by ant scent marks, they can learn to use them as informative signals while foraging on artificial flowers. 4. To test for similar activity in the wild, visitor behaviours at the flowers of Digitalis purpurea Linnaeus, Bupleurum fruticosum Linnaeus, and Brassica juncea (Linnaeus) Czernajew were compared between flowers that had been in contact with ants and those that had not. No differences were found between the two treatments. 5. The use of chemical foraging cues by bees would appear to be strongly dependent on previous experience and in the context of these plant species bees did not associate ant scent mark cues with foraging costs.     

Floral preferences of hoverflies (Diptera: Syrphidae) in response to the abundance and species richness of flowering plants

For understanding the relationship between floral resources and the abundance of hoverflies, five meadows were selected at different elevations in a forested region. At each site the number of flowering herbaceous plants was assessed along a transect at 10-m intervals. To measure floral density, we counted the number of open flowers per species in each plot. Hoverflies visiting flowering plants were captured in each plot during 10 minutes. Path analysis showed that there was a negative correlation between plant species richness and syrphid abundance. Flower abundance had a strong positive direct effect on syrphid abundance but had indirect effects on the number of syrphid species. Only altitude had a strong positive direct effect on the number of syrphid species and this may be explained by the different climatic conditions. Some plant species attracted more syrphids than others. There were significantly fewer species of hoverfly per plot with increasing numbers of flowers. We interpret this to mean that plant species with a high density of flowers attracted more syrphids of the same species. Analysis of pollen grains extracted from two species of hoverflies showed that flower constancy occurred in three examined sites.     

Attractiveness of common insectary and harvestable floral resources to beneficial insects

Resources for natural enemies are often lacking in agricultural fields. The provisioning of floral resources in crop fields can ameliorate this problem by providing nectar and pollen to natural enemies. To select an appropriate floral resource, plants must be screened for their flowering times and attractiveness to natural enemies and pests. We tested the attractiveness of nine species of annual flowering plants to hoverflies, which are important predators of aphids in California lettuce fields. We also sampled arthropods in the foliage of tested plants, to assess the abundances of other natural enemy and pest species that were present. Tested plants included three commonly-used insectary plants and six flowering plant species that showed potential as either harvestable herbs or cut flowers. Harvestable insectary plants may provide additional economic incentive for growers to set aside land for floral resources. The commonly-used insectary plant sweet alyssum consistently attracted the most hoverflies and the least bees, while potentially harvestable plants attracted few hoverflies. Competition with bees may have reduced hoverfly visits to several of the tested plant species. Sweet alyssum also stayed in bloom the longest, and contained the highest numbers of predatory hemipterans. Results suggest that plants should be screened for their attractiveness to not only the target biological control agent, but also to other potential competitors for floral resources. While this initial study focused on a limited selection of harvestable annual plants, a wide variety of other marketable plant species, particularly perennials, remain to be tested for their attractiveness to hoverflies or other beneficial arthropods.     

Pollinator visitation closely tracks diurnal patterns in pollen release

Premise

Animal-pollinated plants face a high risk of pollen loss during its transfer. To limit the negative effect of pollen losses by pollen consumption and heterospecific transfer, plant species may adjust and stratify their pollen availability during the day (i.e., “schedule” their pollen presentation) and attract pollinators in specific time frames.

Methods

We investigated diurnal patterns of pollen availability and pollinator visitation in three coflowering plant species: Succisa pratensis with open flowers and accessible pollen, pollinated mainly by pollen-feeding hoverflies; Centaurea jacea with open flowers and less accessible pollen, pollinated mainly by pollen-collecting bees; and Trifolium hybridum with closed flowers and pollen accessible only after the active opening of the flower, pollinated exclusively by bees.

Results

The three plant species differed in the peak pollen availability, tracked by the visitation activity of their pollinators. Succisa pratensis released all pollen in the morning, while pollinator activity was still low and peaked with a slight delay. In contrast, C. jacea and T. hybridum had distinct pollen presentation schedules, peaking in the early afternoon. The pollinator visitation to both of these species closely matched their pollen availability.

Conclusions

Stratifying pollen availability to pollinators during the day may be one of several mechanisms that allow coflowering plants to share their pollinators and decrease the probability of heterospecific pollen transfer.     

Flowers, Nectar and Insect Visits: Evaluating British Plant Species for Pollinator-friendly Gardens

Twenty-four plant species native or naturalized in Britain weregrown in the Cambridge University Botanic Garden, UK and evaluatedas potential resources for nectar-foraging bees, butterfliesand hoverflies. In ten plant species a series of measurementswere made, at regular intervals from dawn to dusk, of nectarsecretion rate and standing crop, and in all species insectvisits were monitored throughout daylight hours. The study revealeddifferences between plant species in the composition of theassemblage of insect visitors, and in the magnitude and temporaldistribution of the nectar reward. In some cases we found interestingcorrelations between temperature and secretion rates or patternsof insect visits. Species that received numerous insect visitsin our study are potentially valuable forage plants that mightbe planted by gardeners to support local pollinator populations.Deep flowers whose nectar is accessible to long-tongued bumblebees(Bombus hortorum, B. pascuorum) but not to honeybees may providelong-tongued pollinators with a resource refuge relatively freefrom honeybee competition. Features that make some of thoseplant species particularly interesting to observe in the gardeninclude robbing by short-tongued bumblebees inSaponaria,baseworkingby honeybees on closed flowers inMalva sylvestris, and apparentdisplacement of bumblebees by territorial behaviour of the solitarybeeAnthidium manicatumon species ofStachys.Copyright 1999 Annalsof Botany Company Wild flowers, gardens, nectar,Silene, Lychnis, Saponaria, Stachys, Malva, Dipsacus fullonum, Lythrum salicaria,pollinators, bumblebees,Bombus,honeybees,Apis,butterflies, Lepidoptera, hoverflies, Syrphidae,Anthidium manicatum, weeds.     

Pollinator guilds respond contrastingly at different scales to landscape parameters of land‐use intensity

Land‐use intensification is the main factor for the catastrophic decline of insect pollinators. However, land‐use intensification includes multiple processes that act across various scales and should affect pollinator guilds differently depending on their ecology. We aimed to reveal how two main pollinator guilds, wild bees and hoverflies, respond to different land‐use intensification measures, that is, arable field cover (AFC), landscape heterogeneity (LH), and functional flower composition of local plant communities as a measure of habitat quality. We sampled wild bees and hoverflies on 22 dry grassland sites within a highly intensified landscape (NE Germany) within three campaigns using pan traps. We estimated AFC and LH on consecutive radii (60–3000 m) around the dry grassland sites and estimated the local functional flower composition. Wild bee species richness and abundance was positively affected by LH and negatively by AFC at small scales (140–400 m). In contrast, hoverflies were positively affected by AFC and negatively by LH at larger scales (500–3000 m), where both landscape parameters were negatively correlated to each other. At small spatial scales, though, LH had a positive effect on hoverfly abundance. Functional flower diversity had no positive effect on pollinators, but conspicuous flowers seem to attract abundance of hoverflies. In conclusion, landscape parameters contrarily affect two pollinator guilds at different scales. The correlation of landscape parameters may influence the observed relationships between landscape parameters and pollinators. Hence, effects of land‐use intensification seem to be highly landscape‐specific.     

Smells like aphids: orchid flowers mimic aphid alarm pheromones to attract hoverflies for pollination

Most insects are dependent on chemical communication for activities such as mate finding or host location. Several plants, and especially orchids, mimic insect semiochemicals to attract insects for unrewarded pollination. Here, we present a new case of pheromone mimicry found in the terrestrial orchid Epipactis veratrifolia. Flowers are visited and pollinated by several species of aphidophagous hoverflies, the females of which also often lay eggs in the flowers. The oviposition behaviour of these hoverflies is mainly guided by aphid-derived kairomones. We show that the flowers produce α- and β-pinene, β-myrcene and β-phellandrene, and that these compounds attract and induce oviposition behaviour in female hoverflies. This floral odour profile is remarkably similar to the alarm pheromone released by several aphid species, such as Megoura viciae. We therefore suggest that E. veratrifolia mimics aphid alarm pheromones to attract hoverflies for pollination; this is the first time, to our knowledge, that such a case of mimicry has been demonstrated.     

Distribution and abundance of aphidophagous hoverflies (Diptera: Syrphidae) in wildflower patches and field margin habitats

1 The spatial and temporal variations in aphidophagous syrphid abundance were recorded over two seasons in wildflower resource patches sown in a winter barley crop and associated field margins. Standard census techniques and sticky board trapping were used to assess numbers of syrphids, whilst weekly flower head counts were used to quantify the floral resources available in each of the patches. 2 The field margin supported a greater diversity and density of syrphids than the within‐crop wildflower patches, despite having a relatively lower flower head density. Presumably this was in response to other resources that field margins offer, namely additional aphid resources, shelter from predation, lekking sites and suitable flight‐paths. 3 The commonest species of syrphid, Episyrphus balteatus, demonstrated a very positive habitat association with the field margin and was rarely reported in the field patches. Therefore, it may be an unsuitable candidate for the biological control of aphids via augmentation of numbers using non‐host resources. 4 Patch size and shape had little effect on the spatial distributions of syrphids, probably because of the adult syrphids' high mobility. 5 Of greater influence was the number of flowers contained in each habitat patch. Typically, patches with higher numbers of flowers had significantly greater aggregations of hoverflies. Habitat manipulation by the provision of flowers in patches seems to increase the local density of hoverflies. Further work is necessary to establish the importance of flower density in enhancing the control of pest populations.     

谁是腊梅的主要传粉者:昆虫行为与传粉作用

访花昆虫不同的访花与飞行行为导致其访花频率小同,进而对植物传粉产生不同的影响.意大利蜜蜂(Apis mellifera ligustica)、苍蝇和食蚜蝇是腊梅(Chimonanthus praecox)最常见的访花类群(或种类),但是它们的访花行为却有很大不同.意大利蜜蜂主要以快速飞行为主,偶见爬行,苍蝇访花时主要以快速飞行、爬行和跳跃为主,而食蚜蝇以长时间单花访问和悬空飞行以及间歇性休息为主.根据访花类群(或种类)在一朵花上的访花时间和花间飞行时间进行推算,每只意大利蜜蜂、苍蝇和食蚜蝇每分钟分别可以访问4.57、2.65和0.53朵花.结合每种(类)昆虫的访花数量推算出意大利蜜蜂、苍蝇和食蚜蝇每分钟分别可以访问498.19、1,089.74和99.78朵花.传粉效力(相同条件下单位时间内相同数目访花者能够授粉的花朵数)实验结果证明苍蝇和意大利蜜蜂分别是93％、100％(n=30),而食蚜蝇只有13％(n=30).苍蝇和意大利蜜蜂可携带大量花粉且具有很高的传粉效力,因此,访花速度的快慢是二者访花能力强弱的主要限制因素.由此,我们认为苍蝇可能是腊梅最主要的传粉者,意大利蜜蜂次之(数量偏少),食蚜蝇再次(访花与飞行行为的影响以及访花效力较低是限制其访花能力的主要因素).     

The attractiveness of flowering herbaceous plants to bees (Hymenoptera: Apoidea) and hoverflies (Diptera: Syrphidae) in agro‐ecosystems of Central Spain

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Hoverfly (Diptera: Syrphidae) community of a cultivated arable field and the adjacent hedgerow near Debrecen,Hungary

A hoverfly (Syrphidae) community was investigated in a cultivated wheat field and the adjacent hedgerow near Debrecen (Hungary). We monitored the change of species richness and abundance of hoverflies along three transects in the hedgerow and in the wheat field in different distances (10 m, 20 m) from the hedgerow. The effect of sampling methods on the number of hoverfly species and individuals was analyzed. Two sampling methods were used to catch hoverflies: netting and pan traps. The whole sampling period was divided into three subperiods, which are early (22^nd April–2^nd June), middle (11^th June–1^st August) and late (6^th August–11^th September). Altogether 1,214 individuals of 22 species were sampled. Fourteen species with 78% of individuals belonged to the aphidophagous group, feeding on aphids as larvae. Altogether 861 individuals of 22 hoverfly species were sampled by netting and 353 individuals of 10 species by pan traps. The total number of hoverfly species was significant lower in the late period than in the early. The total abundance was higher in the middle period compared to the early. The species richness and abundance of aphidophagous species followed a similar pattern as the total species values. The species richness and abundance of hoverflies were significant higher in 10 m and 20 m distance in the wheat field than along the hedgerow. The results suggest that the pan traps were less efficient in the hedgerow than the netting, but in the wheat field they sampled more hoverflies because of visually alluring effect on hoverflies in the absence of flowers.     

What colour of flowers do Lepidoptera prefer for foraging?

Food plant preferences of some Lepidoptera species associated with particular colour of the flowers were investigated. Based on 1,329 field observations of 43 Lepidoptera and 66 plant species, Lepidoptera showed a high tendency (G-test, G _adj = 698.6, df = 6, P < 0.001) to use the yellow (29%) and pink (28%) coloured flowers for foraging. Compared to the other colours it was evident that plants with red flowers (2%) were not preferred. Moreover, the plants with red (H = 0.435) and yellow-white (H = 0.543) flowers were not visited by diverse Lepidoptera species. Although yellow and pink flowers were most frequently visited, the highest degrees of the Lepidoptera diversity values were associated with the plants having blue (H = 0.647) and purple (H = 0.634) flowers. Species of Nymphalidae were most numerous (14 spp.) in the study area and the members of this family were observed 430 times on 39 different plant species, but never on plants with red flowers. Pieris rapae was the most abundant species that occurred 136 times on a total of 21 different plant species of which eight had yellow flowers. But, this species has never been seen while feeding on red flowers.     

An ancient pollinator of a contemporary plant (Cyclamen persicum): When pollination syndromes break down

Pollination of Cyclamen persicum (Primulaceae) was studied in two wild populations in Israel. Buzz-pollination proved to be extremely rare, and performed by a large Anthophora bee only. The most frequent pollinators were various unspecialized species of thrips (Thysanoptera) and hoverflies (Syrphidae). In the Winter-flowering populations the commonest visitor was a small primitive moth, Micropteris elegans (Micropterigidae, Lepidoptera). These moths feed on pollen, copulate and oviposit within the flowers. From the rarity of buzz-pollination it is concluded that the genus Cyclamen co-evolved with large bees capable of buzz-pollination, but lost its original pollinators for unknown historical reasons. The vacant niche was then open to various unspecialized pollen consumers such as thrips, hoverflies and small solitary bees. While these insects are not specific to C. persicum and seem to play a minor role only, the moth strictly relies upon Cyclamen and seems to be the most efficient pollinator.     

Hedgerows surrounding organic apple orchards in north‐west Spain: potential to conserve beneficial insects

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Evaluation of pollinator effectiveness based on pollen deposition and seed production in a gynodieocious alpine plant,Cyananthus delavayi

Examining variations in pollinator effectiveness can enhance our understanding of how pollinators and plants interact. Pollen deposition and seed production after a single visit by a pollinator are often used to estimate pollinator effectiveness. However, seed production is not always directly related to pollen deposition because not all pollen grains that are deposited on a stigma are compatible or conspecific. In the field, we tested pollinator effectiveness based on pollen deposition and the resulting seed production after single visits by different pollinator groups in a gynodieocious alpine plant Cyananthus delavayi (Campanulaceae). Our results showed that mean pollen deposition was generally inconsistent with mean seed production when comparisons were performed among different pollinator groups and sexes. In general, the correlations were not significant between pollen deposition and seed production in both perfect and female flowers after single visits by halictid bees, bumble bees, and hoverflies. We suggest seed set of virgin flowers after single visits is a more reliable indicator of pollinator effectiveness than pollen deposition and would be a better indicator of pollinator effectiveness for future studies.     

Reproductive biology of the Red List species Polemonium caeruleum (Polemoniaceae)

The majority of flowering plants, including many rare and threatened species, are pollinated by animals, but little is known of pollination and breeding systems of many endangered species. Polemonium caeruleum (Polemoniaceae) is a red‐listed species and is regarded as dichogamous, self‐compatible and bee pollinated. However, some studies show that it is visited by a vast assemblage of anthophilous insects from many taxonomic orders and that breeding systems vary greatly between closely related taxa of this genus. Over a period of 3 years we investigated breeding system, dichogamy, nectar secretion and composition, insect visitations and pollen loads in flowers of P. caeruleum in north‐eastern Poland to determine whether the reproductive biology of the plant explains its rarity. Contrary to published data, our study plants were self‐incompatible and showed a high degree of outcrossing. Our experimental work confirmed the occurrence of protandry in this species, revealed that nectar is sucrose‐dominant and proline‐rich and, for the first time for Polemoniaceae, that nectar secretion and nectar sugar concentration in flowers of P. caeruleum is female‐biased. Although flowers were visited by at least 39 species of insects from five taxonomic orders, overall the plant exhibited many characters associated with bee pollination, and analysis of insect performance showed that bumblebees and honeybees are the key pollinators; occasionally hoverflies and butterflies may also be involved. We conclude that, in terms of pollination system, P. caeruleum demonstrates high apparent generalization, but low realized generalization, and is a functional specialist, as most pollinators belong to a single functional group (guild). Its conservation status, at least in our study population, cannot be explained in terms of the biological properties of its breeding or pollination systems; rather, the present decline of the species is caused by habitat loss. However, if this process and bumblebee decline in Europe continue, P. caeruleum populations may diminish in numbers and density and, owing to the self‐incompatibility of the species, quickly become severely pollen‐limited, thereby accelerating further local extinctions. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173 , 92–107.     

An exceptionally high diversity of hoverflies (Syrphidae) in the food of the reed warbler (Acrocephalus scirpaceus)

Despite being considered a classical example of protective Batesian mimicry hoverflies (Syrphidae) are known to be preyed upon by various passerines. The aim of the present study was to examine in detail food brought by reed warblers Acrocephalus scirpaceus to their nests to better understand the importance of hoverflies in the diet of small passerines. Using neck collars, 273 food samples containing 8,545 food items delivered to reed warbler and parasitic common cuckoo Cuculus canorus nestlings in warbler nests were recorded. The study was conducted during three breeding seasons in South Moravia, Czech Republic. An unusually high diversity of hoverflies was found — 27 species, including Mesembrius peregrinus (critically endangered species in the Czech Republic) and Mallota cimbiciformis (endangered species) — a new taxon to the Czech Republic. This indicates that nestling diet analyses may provide not only information on avian foraging behaviour but also important faunistic data. Thus, without the detailed identification to species level of material from foraging behaviour studies valuable scientific information may be lost. Overall dominance of Syrphidae was 3.7%, the most common species being Episyrphus balteatus (55.7%, n = 318). However, this number seriously underestimates the importance of hoverflies in the diet of reed warblers as hoverflies are one of the largest prey taken by warblers. Both larvae and pupae were rare, imagines strongly dominating (92.7%). Both specific wasp mimics (e.g., Chrysotoxum verrali) and bee mimics (e.g., Eristalis spp.) were not avoided by foraging reed warblers. The presence of a parasitic cuckoo chick did not affect host foraging behaviour with respect to overall dominance of hoverflies in the diet (warbler 3.3%, cuckoo 3.8%).     

Hoverflies (Diptera: Syrphidae) benefit from a cultivation of the bioenergy crop Silphium perfoliatum L. (Asteraceae) depending on larval feeding type,landscape composition and crop management

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Breeding system of the critically endangered Lakela’s Mint and influence of plant height on pollinators and seed output

Understanding reproductive systems of rare plants is critical for conservation efforts. Lakela's Mint, Dicerandra immaculata Lakela var. immaculata, is an endangered plant endemic to an approximately 4.8-km long area in Florida, USA. We used an experimental garden and three populations of Lakela's Mint to determine: (1) what is the breeding system (autonomous, asexual, self-fertile, cross-fertile) and are insects necessary for reproduction; (2) which native and nonnative insect species visit flowers and is the frequency of visits to a plant influenced by its height; (3) does the number of flowers visited within a plant by individual insects differ among native and nonnative insect species and due to plant height; and (4) is seed output influenced by plant height? Our results indicate that the breeding system of Lakela's Mint was facultative outcrossing. Insect-pollinated flowers produced more seeds than flowers that reproduced autonomously or asexually. The honey bee Apis mellifera L., a nonnative species, was the most frequent visitor to plants and visited more flowers within plants than native pollinators, but its behavior was not influenced by plant height. Native pollinators such as Bombus impatiens Cresson were attracted more frequently to shorter plants, but visited fewer flowers than on taller plants. Despite having fewer total and pollinated flowers, shorter plants had a higher output of intact seeds than taller plants, which could be due to differences in efficiency between native and nonnative pollinators or other factors. Our results add insight into factors influencing seed output and interactions between pollinators and rare plants.