Morphology of nectaries and biology of nectar production in the distylous species Fagopyrum esculentum

No evidence for competition over floral resources between winter-active parasitoids and pollinators in agroecosystems

Warming temperate winters are resulting in increased insect winter activity. With modern agroecosystems largely homogenous, characterised by low floral diversity, competitive interactions may arise between flower-visiting species, with potential implications for the ecosystem services they provide (e.g. biological control and pollination). Flower strips may be implemented during winter months to support flower-visiting insects and enhance ecosystem service provision. Employing field trials conducted in Brittany, France between 2019 and 2021 and laboratory cage experiments, the current study examined the impact of winter flower strips on aphid biological control performed by parasitoid wasps and the potential for competitive interactions between winter-active parasitoids and pollinators. Results revealed that parasitism rate was not enhanced by the presence of winter flower strips. This lack of effect was not the consequence of pollinator presence, and the current study found no effect of pollinator abundance on parasitism rate. Flower strips may thus be implemented during winter months to support nectar-feeding insects when floral resources are scarce, with no evidence of exploitative competition between pollinators and parasitoids, nor a detrimental impact on biological control provision.

The yield of common buckwheat (Fagopyrum esculentum Moench) depends on the genotype but not on the Pin-to-Thrum ratio

Common buckwheat has a complicated flowering biology. It is characterized by a strong self-incompatibility resulting from heterostyly, i.e. the occurrence of two types of flowers: Pin and Thrum, differing in the length of pistils and stamens. Fertilization occurs only as a result of cross-pollination between these morphs. Suspicions exist that the disturbed ratio between plants producing Pin and Thrum flowers (with the latter type generating more seeds) causes low seed yield. The aim of the study was to analyze: (1) the ratio between plants with Pin and Thrum morphs, (2) flower and seed production, as well as abortion of flowers, (3) the composition of nectar collected at an early flowering stage and during full flowering. The study was performed under semi-controlled and field conditions on six Polish accessions. The results indicated that under semi-controlled conditions the Pin-to-Thrum ratio was indeed disproportionate; such a phenomenon is called anisoplethy. In the field, however, the Pin-to-Thrum ratio was well-balanced (isoplethy). The plants with both morphs aborted a similar percentage of flowers and produced a comparable number of empty seeds. The number of flowers, their abortion, and ripe seed production were independent of flower type, however, they were genotypically controlled. A strong correlation between the number of flowers produced by a plant, flower abortion and the number of empty seeds was found. The percentage of aborted flowers correlated positively with the weight of ripe seeds. Nectar composition was similar for all buckwheat genotypes, but we found some differences in the amount of individual sugars depending on the blooming stage. In the majority of accessions, the nectar produced at the early blooming stage was characterized by a greater mass and volume, and contained more individual sugars than at the full-flowering stage.

The Effect of Stimulants on Nectar Composition, Flowering, and Seed Yield of Common Buckwheat (Fagopyrum esculentum Moench)

Common buckwheat is a valuable plant producing seeds containing a number of health-promoting compounds and elements. Buckwheat does not contain gluten and is characterized by an excellent composition of amino acids. This species is also a melliferous plant. Despite many advantages, the area of buckwheat cultivation is decreasing due to unstable yields. One of the reasons for low seed yield is its sensitivity to drought, high temperatures, and assimilate deficiencies. These factors have a significant impact on the nectar composition, which is important for visiting pollinators and thus for pollination. High temperature during flowering increases the degeneration of embryo sacs and embryos, which is high anyway (genetic determination) in common buckwheat. This phenomenon seems to be unbreakable by breeding methods. The authors aimed to determine whether stimulants commonly used in agriculture could increase the seed yield of this plant species. The aim of the work was to choose from eight different stimulants the most effective one that would improve the seed yield of two accessions of common buckwheat by increasing the efficiency of nectar production and reducing the number of empty seeds. The plants were sprayed at either the beginning of flowering or at full bloom. The content of sugars and amino acids was higher in the nectar produced at the beginning of flowering. The nectar of both lines included also polyamines. The level of sugars in the nectar increased mainly after spraying with the stimulants in the second phase of flowering. A positive correlation between the total amount of sugars and amino acids in the nectar and seed yield was found. All the stimulants used reduced the number of empty seeds in both accessions. Seed production in the PA15 line increased significantly under the influence of all stimulants used at the beginning of flowering, and the most effective were ASAHI SL and TYTANIT®.

Features of floral odor and nectar in the distylous Luculia pinceana (Rubiaceae) promote compatible pollination by hawkmoths

It is hypothesized that in heterostylous plant species, standardization of signals of floral attraction between different morphs is advantageous, encouraging flower visitors to switch between morphs. It remains unclear whether signals of floral attraction (floral odor and properties of nectar) are similar between morphs in distylous species pollinated by hawkmoths, and how these relate to hawkmoth behavior. We observed the behavior of visitors to distylous Luculia pinceana (Rubiaceae), collected and analyzed floral odor, and examined properties of nectar (volume, sugar concentration, and composition) of long‐styled and short‐styled morphs during the day and night. Pollinator responses to the floral scent were tested with a Y‐tube olfactometer. We conducted diurnal and nocturnal pollination treatments and six other pollination treatments to test the importance of nocturnal pollinators and to examine the self‐incompatibility system. A species of hawkmoth, Cechenena lineosa, was the effective pollinator. The floral odor was rich in methyl benzoate, and sucrose was dominant in the nectar. There were no significant differences between the two morphs in the methyl benzoate content or the properties of nectar. Flowers released more methyl benzoate and secreted larger volumes of nectar with lower sugar concentration at night than during the day. The hawkmoth had a significant preference for methyl benzoate. Luculia pinceana was partially self‐incompatible and relied on nocturnal pollinators for reproductive success. This study verifies that floral attraction signals are consistent between different morphs in this distylous species, promoting compatible pollination, and the features and the diel pattern of these signals between day and night are adapted to hawkmoth behavior.

Nectar-Inhabiting Bacteria Affect Olfactory Responses of an Insect Parasitoid by Altering Nectar Odors

Floral nectar is ubiquitously colonized by a variety of microorganisms among which yeasts and bacteria are the most common. Microorganisms inhabiting floral nectar can alter several nectar traits, including nectar odor by producing microbial volatile organic compounds (mVOCs). Evidence showing that mVOCs can affect the foraging behavior of insect pollinators is increasing in the literature, whereas the role of mVOCs in altering the foraging behavior of third-trophic level organisms such as insect parasitoids is largely overlooked. Parasitoids are frequent visitors of flowers and are well known to feed on nectar. In this study, we isolated bacteria inhabiting floral nectar of buckwheat, Fagopyrum esculentum (Polygonales: Polygonaceae), to test the hypothesis that nectar bacteria affect the foraging behavior of the egg parasitoid Trissolcus basalis (Hymenoptera: Scelionidae) via changes in odors of nectar. In behavioral assays, we found that T. basalis wasps are attracted toward nectar fermented by 4 out of the 14 bacterial strains isolated, which belong to Staphylococcus epidermidis, Terrabacillus saccharophilus (both Firmicutes), Pantoea sp. (Proteobacteria), and Curtobacterium sp. (Actinobacteria). Results of chemical investigations revealed significant differences in the volatile blend composition of nectars fermented by the bacterial isolates. Our results indicate that nectar-inhabiting bacteria play an important role in the interactions between flowering plants and foraging parasitoids. These results are also relevant from an applied perspective as flowering resources, such as buckwheat, are largely used in agriculture to promote conservation biological control of insect pests.

Unravelling rutin content of tartary buckwheat of north western Himalayas and insights into nucleotide polymorphisms in PAL gene to infer the associations with rutin biosynthesis

Buckwheat (Fagopyrum spp.) has immense nutritional and nutraceutical potential. All the plant parts of buckwheat possess various metabolites, such as rutin, quercetin, vitexin etc. The high content of rutin in this pseudo cereal crop strongly adapts it to grow under adverse environments. In the present study 50 germplasm lines of Fagopyrum tataricum were used for estimation of seed endosperm rutin content through HPLC. Furthermore, molecular analysis of PAL gene (Phenylalanine Ammonia Lyase), an upstream gene in rutin biosynthesis pathway was targeted for detection of SNPs to understand the variations in the concentrations of seed endosperm rutin content, among tartary buckwheat genotypes with highest and lowest seed endosperm rutin content. Three primer pairs were employed for amplification of PAL gene for F. tartaricum (covering whole gene) followed by sequencing. Rutin concentration in seed endosperm of F. tartaricum ranged from 194.86 to 1403.22 ppm with an average of 617.06 ppm. Highest rutin concentration was found in genotype BWZ90 and lowest in BWZ16. Significant variations were observed in the seed endosperm rutin content among the genotypes of tartary buckwheat. Furthermore, alignment of PAL gene sequences of genotypes with high seed endosperm rutin content and low seed endosperm rutin content revealed variations at 21 polymorphic sites. The amino acid sequences obtained from the nucleotide sequences were also aligned and the variations were detected at 19 positions. The putative protein structure showed conformational changes among predicted proteins from two contrasting genotypes for endosperm rutin content. We here established an inventory of seed endosperm rutin content of tartary buckwheat. This study also provided insights about role of these SNPs in rutin biosynthesis. Furthermore, this information can be used for breeding buckwheat for high metabolite contents.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03218-y.

Polyphenol profile of buckwheat honey, nectar and pollen

A focus of research in recent years is the comparison of honey as the final product of bees with pollen and nectar of the plant from which the honey originates, as the main food source for bees. Buckwheat honey is recognized as a nutritionally valuable product, which provides a scientifically proven health benefit and is confirmed as a functional food. The quality of this type of honey is attributed to high levels of phytochemicals in buckwheat. The purpose of this study was the examination of similarity between buckwheat honey and buckwheat nectar and pollen, as well as simultaneous investigation of their chemical profiles and the origin of the honey. The phenolic profile of buckwheat pollen showed a lower number of flavonoids and phenolic acids than those of nectar and honey samples, but confirmed the presence of the most characteristic polyphenols derived from the buckwheat plant. The notable difference was found to be the presence of (epi)catechin units, its galloylated derivatives and procyanidin dimers, which were not present in honey. Honey polyphenols displayed a pronounced correlation with those of nectar, but not with those of pollen. Finally, by comparing the polyphenolic profiles of honey, nectar and pollen sharing the same geographical origin, new data could be provided for a potential assessment of the botanical origin of buckwheat honey.

Influence of light, dark, temperature and drought on metabolite and ion composition in nectar and nectaries of an epiphytic bromeliad species (Aechmea fasciata)

Research into the influence of stress factors, such as drought, different temperatures and/or varied light conditions, on plants due to climate changes is becoming increasingly important. Epiphytes, like many species of the Bromeliaceae, are particularly affected by this, but little is known about impacts on nectar composition and nectary metabolism. We investigated the influence of drought, different temperatures and light-dark regimes on nectar and nectaries of the epiphytic bromeliad species, Aechmea fasciata, and also the influence of drought with the terrestrial bromeliad, Billbergia nutans. The content of sugars, amino acids and ions in nectar and nectaries was analysed using HPLC. In addition, the starch content and the activities of different invertases in nectaries were determined. Compositions of nectar and nectaries were hardly influenced, neither by light nor dark, nor by different temperatures. In contrast, drought revealed changes in nectar volumes and nectar sugar compositions in the epiphytic bromeliad as well as in the terrestrial bromeliad. In both species, the sucrose-to-hexose ratio in nectar decreased considerably during the drought period. These changes in nectar sugar composition do not correlate with changes in the nectaries. The total sugar, amino acid and ion concentrations remained constant in nectar as well as in nectaries during the drought period. Changes in nectar composition or in the production of floral pollinator rewards are likely to affect plant-pollinator interactions. It remains questionable how far the adaptations of the bromeliads to drought and diverse light or temperature conditions are still sufficient.

Nutraceutical crop buckwheat: a concealed wealth in the lap of Himalayas

Buckwheat is a crop that has gained considerable interest worldwide due to its nutritional, economical, and pharmaceutical values. To ensure food and nutritional security in a scenario of global climate change, this pseudocereal is a competent alternative to staple crops. With rising knowledge regarding the nutraceutical potential, the popularity of this species is expected to increase further in coming years. The main bioactive component of this species is rutin that has been proven to have a wide range of health-promoting benefits. Due to breeding constraints, asynchronous maturity, seed shattering, and restricted distribution, this species holds the status of an underutilized or neglected crop in many parts of the world. In the North-western Himalayan zone, it is an integral part of local dietary intake and is grown as a second crop after harvesting barley and peas. Fagopyrum esculentum and F. tataricum are the species of buckwheat cultivated in the North-western Himalayas. However, more studies in the direction of conservation, utilization, and genetic amelioration of plant genetic resources are needed to sustain food security in Southeast Asia. The present review paper accentuates the multicore potential of buckwheat besides highlighting the commercial and pharmaceutical perspective. This article also focuses on the conservation and sustainable utilization of Himalayan gene pools, desirable agronomic traits, and genetic diversity besides focusing on the biochemical and molecular response of Fagopyrum to biotic and abiotic stress including modulation of the rutin content. The role of biotechnological interventions and future prospects are also summarized.

Healthy and Resilient Cereals and Pseudo-Cereals for Marginal Agriculture: Molecular Advances for Improving Nutrient Bioavailability

With the ever-increasing world population, an extra 1.5 billion mouths need to be fed by 2050 with continuously dwindling arable land. Hence, it is imperative that extra food come from the marginal lands that are expected to be unsuitable for growing major staple crops under the adverse climate change scenario. Crop diversity provides right alternatives for marginal environments to improve food, feed, and nutritional security. Well-adapted and climate-resilient crops will be the best fit for such a scenario to produce seed and biomass. The minor millets are known for their high nutritional profile and better resilience for several abiotic stresses that make them the suitable crops for arid and salt-affected soils and poor-quality waters. Finger millet (Eleucine coracana) and foxtail millet (Setaria italica), also considered as orphan crops, are highly tolerant grass crop species that grow well in marginal and degraded lands of Africa and Asia with better nutritional profile. Another category of grains, called pseudo-cereals, is considered as rich foods because of their protein quality and content, high mineral content, and healthy and balance food quality. Quinoa (Chenopodium quinoa), amaranth (Amaranthus sp.), and buckwheat (Fagopyrum esculentum) fall under this category. Nevertheless, both minor millets and pseudo-cereals are morphologically different, although similar for micronutrient bioavailability, and their grains are gluten-free. The cultivation of these millets can make dry lands productive and ensure future food as well as nutritional security. Although the natural nutrient profile of these crop plant species is remarkably good, little development has occurred in advances in molecular genetics and breeding efforts to improve the bioavailability of nutrients. Recent advances in NGS have enabled the genome and transcriptome sequencing of these millets and pseudo-cereals for the faster development of molecular markers and application in molecular breeding. Genomic information on finger millet (1,196 Mb with 85,243 genes); S. italica, a model small millet (well-annotated draft genome of 420 Mb with 38,801 protein-coding genes); amaranth (466 Mb genome and 23,059 protein-coding genes); buckwheat (genome size of 1.12 Gb with 35,816 annotated genes); and quinoa (genome size of 1.5 Gb containing 54,438 protein-coding genes) could pave the way for the genetic improvement of these grains. These genomic resources are an important first step toward genetic improvement of these crops. This review highlights the current advances and available resources on genomics to improve nutrient bioavailability in these five suitable crops for the sustained healthy livelihood.

Ecosystem-Based Incorporation of Nectar-Producing Plants for Stink Bug Parasitoids

Adult parasitoids of pest insects rely on floral resources for survival and reproduction, but can be food-deprived in intensively managed agricultural systems lacking these resources. Stink bugs are serious pests for crops in southwest Georgia. Provisioning nectar-producing plants for parasitoids of stink bugs potentially can enhance biocontrol of these pests. Knowledge of spatial and temporal availability and distribution of stink bugs in host plants is necessary for appropriate timing and placement of flowering plants in agroecosystems. Stink bugs move between closely associated host plants throughout the growing season in response to deteriorating suitability of their host plants. In peanut-cotton farmscapes, stink bugs develop in peanut, and subsequently the adults disperse into adjacent cotton. Parasitism of Nezara viridula (L.) adults by Trichopoda pennipes (F.) at the peanut-cotton interface was significantly higher in cotton with a strip of milkweed or buckwheat between the two crops than in cotton alone. Milkweed and buckwheat also provided nectar to a wide range of insect pollinators. Monarch butterflies fed on milkweed. When placed between peanut and cotton, a strip of soybean was an effective trap crop for cotton, reducing economic damage. Incorporation of buckwheat near soybean enhanced parasitism of Euschistus servus (Say) eggs by Telenomus podisi Ashmead in cotton. In conclusion, nectar provision enhances biocontrol of stink bugs, acts together with other management tactics for stink bug control, and aids in conservation of natural enemies, insect pollinators, and the monarch butterfly.

Nectar Attracts Foraging Honey Bees with Components of Their Queen Pheromones

Floral nectar often contains chemicals that are deterrent to pollinators, presenting potential challenges to outcrossing plant species. Plants may be able to co-opt pollinator chemical signals to mitigate the negative effects of nectar deterrent compounds on pollination services. We found that buckwheat (Fagopyrum esculentum) and Mexican sunflower (Tithonia diversifolia) produce nectar with abundant phenolics, including three components of the Apis honeybee queen mandibular pheromone (QMP). In addition, these nectars contain a non-pheromonal phenolic, chlorogenic acid (CA), which was toxic to honeybees, and T. diversifolia nectar also contained isochlorogenic acid (IA). Fresh nectar or solutions containing nectar phenolics reduced Apis individual feeding compared to sucrose solutions. However, freely foraging bees preferred solutions with QMP components to control solutions, and QMP components over-rode or reversed avoidance of CA and IA. Furthermore, prior exposure to the presence or just the odor of QMP components removed the deterrent effects of CA and IA. By mimicking the honey bee pheromone blend, nectar may maintain pollinator attraction in spite of deterrent nectar compounds.

Trap Cropping Systems and a Physical Barrier for Suppression of Stink Bugs (Hemiptera: Pentatomidae) in Cotton

Euschistus servus (Say), Nezara viridula (L.), and Chinavia hilaris (Say) (Hemiptera: Pentatomidae) are economic pests of cotton in the coastal plain of the southeastern United States. The objective of this 2-yr study was to determine the ability of trap cropping systems, pheromone-baited stink bug traps, and a synthetic physical barrier at the peanut-to-cotton interface to manage stink bugs in cotton. The physical barrier was the most effective management tactic. Stink bug density in cotton was lowest for this treatment. In 2010, boll injury was lower for the physical barrier compared to the other treatments except for soybean with stink bug traps. In 2011, boll injury was lower for this treatment compared to the control. Soybean was an effective trap crop, reducing both stink bug density in cotton and boll injury regardless if used alone or in combination with either stink bug traps or buckwheat. Incorporation of buckwheat in soybean enhanced parasitism of E. servus egg masses by Telenomus podisi Ashmead in cotton. The insertion of eyelets in the lid of the insect-collecting device of a stink bug trap allowed adult stink bug parasitoids, but not E. servus, to escape. Stand-alone stink bug traps were not very effective in deterring colonization of cotton by stink bugs or reducing boll injury. The paucity of effective alternative control measures available for stink bug management justifies further full-scale evaluations into these management tactics for control of these pests in crops.

Insect pollination and self-incompatibility in edible and/or medicinal crops in southwestern China, a global hotspot of biodiversity

An increasing global demand for food, coupled with the widespread decline of pollinator diversity, remains an international concern in agriculture and genetic conservation. In particular, there are large gaps in the study of the pollination of economically important and traditionally grown species in China. Many plant species grown in China are both edible and used medicinally. The country retains extensive written records of agricultural and apicultural practices, facilitating contemporary studies of some important taxa. Here, we focus on Yunnan in southwestern China, a mega-biodiversity hotspot for medicinal/food plants. We used plant and insect taxa as model systems to understand the patterns and consequences of pollinator deficit to crops. We identified several gaps and limitations in research on the pollination ecology and breeding systems of domesticated taxa and their wild relatives in Yunnan and asked the following questions: (1) What is known about pollination systems of edible and medicinal plants in Yunnan? (2) What are the most important pollinators of Codonopsis subglobosa (Campanulaceae)? (3) How important are native pollinator species for maximizing yield in Chinese crops compared with the introduced Apis mellifera? We found that some crops that require cross-pollination now depend exclusively on hand pollination. Three domesticated crops are dependent primarily on the native but semidomesticated Apis cerana and the introduced A. mellifera. Other species of wild pollinators often play important roles for certain specialty crops (e.g., Vespa velutina pollinates Codonopsis subglobosa). We propose a more systematic and comprehensive approach to applied research in the future.

Ectopic expression of FaesAP3, a Fagopyrum esculentum (Polygonaceae) AP3 orthologous gene rescues stamen development in an Arabidopsis ap3 mutant

Arabidopsis thaliana APETALA3 (AP3) and Antirrhinum majus DEFICIENS (DEF) MADS box genes are required to specify petal and stamen identity. AP3 and DEF are members of the euAP3 lineage, which arose by gene duplication coincident with radiation of the core eudicots. In order to investigate the molecular mechanisms underlying organ development in early diverging clades of core eudicots, we isolated and identified an AP3 homolog, FaesAP3, from Fagopyrum esculentum (buckwheat, Polygonaceae), a multi-food-use pseudocereal with healing benefits. Protein sequence alignment and phylogenetic analyses revealed that FaesAP3 grouped into the euAP3 lineage. Expression analysis showed that FaesAP3 was transcribed only in developing stamens, and differed from AP3 and DEF, which expressed in developing petals and stamens. Moreover, ectopic expression of FaesAP3 rescued stamen development without complementation of petal development in an Arabidopsis ap3 mutant. Our results suggest that FaesAP3 is involved in the development of stamens in buckwheat. These results also suggest that FaesAP3 holds some potential for biotechnical engineering to create a male sterile line of F. esculentum.

Physical barriers for suppression of movement of adult stink bugs into cotton

Nezara viridula (L.), Euschistus servus (Say), and Chinavia hilaris (Say) (Heteroptera: Pentatomidae) are economic pests of cotton in the southeastern USA. Because adult stink bugs exhibit edge-mediated dispersal at crop-to-crop interfaces as they colonize cotton, strategic placement of physical barriers at these interfaces could manage these pests. The objective of this study was to determine the effectiveness of a physical barrier, either synthetic or plant-based, at the peanut-to-cotton interface for suppressing stink bugs that would move to cotton. In 2012 and 2013, sorghum sudangrass (2.4 and 2.1 m high, respectively) was significantly taller than cotton (1.4 and 1.3 m high, respectively) which was taller than peanut (0.4 and 0.5 m high, respectively). Buckwheat (0.6 m high), planted only in 2012, was significantly taller than peanut, but shorter than cotton. For both years of the study, sorghum sudangrass and a 1.8-m-high polypropylene barrier wall effectively deterred dispersal of stink bugs into cotton. Because each of these barriers was taller than cotton, their success in protecting cotton likely was due to disruption of the flight of stink bugs from low-growing peanut into cotton. The shortest barrier wall (0.6-m-high) did not suppress stink bug dispersal into cotton probably because it was approximately the same height as peanut. In 2012, flowering buckwheat increased the efficacy of Trichopoda pennipes (F.) attacking N. viridula in cotton although it did not deter dispersal of stink bugs. In conclusion, a barrier at least as tall as cotton can effectively retard the entry of stink bug adults into cotton.

The effect of floral resources on parasitoid and host longevity: prospects for conservation biological control in strawberries

The strawberry tortricid, Acleris comariana Lienig and Zeller (Lepidoptera: Tortricidae) is an important pest in Danish strawberry production. Its most common parasitoid is Copidosoma aretas (Walker) (Hymenoptera: Chalcidoidea: Encyrtidae). To identify selective flowering plants that could be used to increase functional biodiversity, the longevity of C. aretas and its host A. comariana was assessed on 5 flowering species: buckwheat, Fagopyrum esculentum Moench (Caryophyllales: Polygonaceae); borage, Borago officinalis L. (Boraginaceae); strawberry, Fragaria x ananassa Duchesne (Rosales: Rosaceae); phacelia, Phacelia tanacetifolia Bentham (Boraginaceae); and dill, Anethum graveolens L. (Apiales: Apiaceae). Dill was only tested with C. aretas. Sucrose and pollen served as positive controls, and pure water as a negative control. In a subsequent field experiment, A. comariana larval density was assessed at 1, 6, and 11 m distances from buckwheat flower strips in 3 fields. The proportion of field-collected larvae that were parasitized by C. aretas or fungi was assessed. Among the tested floral diets, buckwheat was superior for C. aretas, increasing its longevity by 1.4 times compared to water. Although buckwheat also increased longevity of A. comariana, its longevity and survival on buckwheat, borage, and strawberry was not significantly different, so buckwheat was chosen for field experiments. A. comariana densities in the 3 fields with sown buckwheat flower strips were 0.5, 4.0, and 8.3 larvae per m per row of strawberry respectively. Of the collected larvae, a total of 1%, 39%, and 65% were parasitized by C. aretas, respectively. The density of A. comariana and the proportion parasitized by C. aretas were highly significantly correlated. Distance from floral strips had no significant effect on either A. comariana larval density or on the proportion of individuals parasitized by C. aretas. Few other parasitoids emerged from collected larvae, and no larvae were infected by entomopathogenic fungi. Still, total A. comariana mortality was significantly affected by distance to flower strips, with the highest mortality near the flower strips. As no effect of buckwheat flower strips on C. aretas parasitism was found, the positive effect they had on A. comariana control stems from unknown mortality factors. As literature indicates that buckwheat for flower strips can augment a more complex suite of natural enemies, one such mortality factor could be a non-consumptive predator and/or parasitoid effect, but this requires further study. If confirmed, buckwheat may be utilized together with a selective food plant, once identified.

Anatomy, ultrastructure, and secretory activity of the floral nectaries in Swietenia macrophylla (Meliaceae)

PREMISE OF THE STUDY

While mahogany (Swietenia macrophylla) is one of the most important forest species in the Amazon region, little is known about its reproductive biology. Knowledge about the nectary structure and dynamics of nectar production of this species represent a key step toward understanding its relationship with pollinators. •

METHODS

Mahogany tree floral buds and flowers in anthesis were collected, fixed, and processed for study by light and transmission and scanning electron microscopy. The chemical composition of nectar and the nectary pigments was also studied. •

KEY RESULTS

Both staminate and pistillate flowers have nectaries, which contain a papillose epidermis and stomata. The nectariferous tissue is parenchymatous, with the cell cytoplasm primarily containing mitochondria and plastids. Secretory activity initiates at the beginning of anthesis, which occurs at nightfall. Flowers undergoing anthesis become structurally modified, with starch grains in the plastids disappearing. The number of plastoglobuli in the plastids also increases when nectaries change color from pale yellow to intense red. Pistillate and staminate flowers produce meager nectar rewards. •

CONCLUSIONS

Changes in plastoglobuli number seem to be related to an increase in carotenes and color changes during anthesis. Carotenes can be linked to the protection of the plant against oxidative stress, which results from secretory activities. Nectary color has a limited role as a pollinator attractant. Floral rewards comprise small nectar droplets in both flower types, in addition to a few pollen grains in staminate flowers. These meager rewards are probably adapted to attract small generalist insects.

Effects of defoliation and shading on the physiological cost of reproduction in silky locoweed Oxytropis sericea

BACKGROUND

The production of flowers, fruits and seeds demands considerable energy and nutrients, which can limit the allocation of these resources to other plant functions and, thereby, influence survival and future reproduction. The magnitude of the physiological costs of reproduction depends on both the factors limiting seed production (pollen, ovules or resources) and the capacity of plants to compensate for high resource demand.

METHODS

To assess the magnitude and consequences of reproductive costs, we used shading and defoliation to reduce photosynthate production by fully pollinated plants of a perennial legume, Oxytropis sericea (Fabaceae), and examined the resulting impact on photosynthate allocation, and nectar, fruit and seed production.

KEY RESULTS

Although these leaf manipulations reduced photosynthesis and nectar production, they did not alter photosynthate allocation, as revealed by (13)C tracing, or fruit or seed production. That photosynthate allocation to reproductive organs increased >190 % and taproot mass declined by 29 % between flowering and fruiting indicates that reproduction was physiologically costly.

CONCLUSIONS

The insensitivity of fruit and seed production to leaf manipulation is consistent with either compensatory mobilization of stored resources or ovule limitation. Seed production differed considerably between the two years of the study in association with contrasting precipitation prior to flowering, perhaps reflecting contrasting limits on reproductive performance.

Asymmetrical legitimate pollination in distylous Palicourea demissa (Rubiaceae): the role of nectar production and pollinator visitation

We investigated morph differences in attributes that contribute to rewarding floral visitors of the distylous shrub Palicourea demissa at La Mucuy cloud forest in Venezuela. In both morphs, we measured nectar production from flowers subjected to repeated removals at 2-h intervals (10 plants per morph) and flowers that accumulated nectar for 24 h (10 plants per morph). In both cases, floral visitors were excluded. In addition, we quantified nectar availability (30 plants per morph), floral visitation (10–12 plants per morph) and legitimate pollination (30 plants per morph) throughout the day. We explored morph differences in the variables mentioned above using analyses of variance, and the effects of nectar variation on floral visitation and legitimate pollination using regression models. We observed 1205 floral visits, grouped into six hummingbird (94.7%) and three insect species (5.3%), across observations (264 h). Coeligena torquata was the most frequent floral visitor (34%) in both morphs (1.4–1.7 visits per plant h−1). Nectar production and availability, and visitation rate were similar between morphs. Visitation rate and legitimate pollen deposition increased with the nectar production in both morphs, but levels of legitimate pollination were higher on short-styled flowers than long-styled flowers. These results show that short-styled and long-styled flowers reward floral visitors equally, but frequency and foraging behaviour of long-billed pollinators can promote asymmetrical legitimate pollination.