Pollinator Density Research Articles

Density, Abundance and Diversity of Insect Pollinators at Agro-Ecosystems of Kodagu District, Karnataka, India

Density, Abundance and Diversity of Insect Pollinators at Agro-Ecosystems of Kodagu District, Karnataka, India

Reviving collapsed plant-pollinator networks from a single species.

Mutualistic ecological networks can suddenly transition to undesirable states due to small changes in environmental conditions. Recovering from such a collapse can be difficult as restoring the original environmental conditions may be infeasible. Additionally, such networks can also exhibit a phenomenon known as hysteresis, whereby the system could exhibit multiple states under the same environmental conditions, implying that ecological networks may not recover. Here, we attempted to revive collapsed mutualistic networks to a high-functioning state from a single species, using concepts from signal propagation theory and an eco-evolutionary model based on network structures of 115 empirical plant-pollinator networks. We found that restoring the environmental conditions rarely aided in recovery of collapsed networks, but a positive relationship between recovering pollinator density and network nestedness emerged, which was qualitatively supported by empirical plant-pollinator restoration data. In contrast, network resurrection from a collapsed state in undesirable environmental conditions where restoration has minimal impacts could be readily achieved by perturbing a single species or a few species that controls the response of the dynamical networks. Additionally, nestedness in networks and a moderate amount of trait variation could aid in the revival of networks even in undesirable environmental conditions. Our work suggests that focus should be applied to a few species whose dynamics could be steered to resurrect entire networks from a collapsed state and that network architecture could play a crucial role in reviving collapsed plant-pollinator networks.

Scenario of Arthropods Fauna on Rose in Southern Rajasthan

The arthropod fauna associated with rose at Udaipur comprised of 17 species of insects (6 pests and 11 pollinators). The pests included were thrips, aphids, the rose bud caterpillar, black flies and the scurfy rose scale while, pollinators included members of Hymenoptera and Diptera. During the crop season, the peak populations of thrips, aphids and larvae of rose bud caterpillar were recorded in the first week of April (9.80 thrips flower buds-1), first week of March (17.04 aphids flower buds-1) and first week of March (0.56 larvae flower-1), respectively. The mean atmospheric temperature evinced a positive correlation with thrips (r=0.832), rose bud caterpillar (r=0.607) and insect pollinators. Thrips (r=0.583) and aphids (r=0.622) had a significant positive correlation with sunshine, whereas the relative humidity indicates significant negative correlation with thrips (r=-0.720), aphids (r=0.581) and rose bud caterpillar (r=-0.817), respectively. The population of pollinators showed a significant positive correlation (r=0.573) with the mean atmospheric temperature; while a significant negative correlation (r=-0.769) with relative humidity. The relative density of pollinators visiting rose comprised: honeybees, A. florae & A. dorsata with 68.24 per cent; solitary bees (12.08%) and dipteran flies (19.55%). Most pollinators preferred to visit rose flowers during 9 to 11 hours of the day

The impact of buckwheat and paulownia (Paulownia elongata × P. fortunei) intercropping on beekeeping value and buckwheat yield

Increasing crop diversity is a way for agriculture to transition towards a more sustainable and biodiversity-friendly system. Growing buckwheat intercropped with paulownia can contribute not only to mitigating climate change but can also enrich the environment with species of agricultural importance, without causing a decline in pollinators, since buckwheat is pollinated mainly by the honeybee. In a field experiment comparing growing buckwheat with paulownia against a monoculture crop, we investigated differences in flower visitation and beekeeping value, as well as the associated impact on crop yields. We analysed the effect of intercropping on the beekeeping value of buckwheat in terms of bee population size and the sugar mass in buckwheat flowers, nectar mass in buckwheat flowers, the quality of the delivered raw sugar and biometric characteristics. We found significant differences in the number of branches on the main shoot and the total number of branches. Significantly higher parameters were obtained in sites with buckwheat monoculture. The cultivation method variant did not cause differentiation in either the structure elements or the yield itself. Yields ranged from 0.39 (2021) to 1.59 (2023) t·ha−1. The average yield in intercropping was slightly lower (0.02 t·ha−1) than in the monoculture system of buckwheat (0.93 t·ha−1). More flowers per plant per day of observation and more flowers in millions of flowers per hectare per day of observation were observed in the intercropping of buckwheat with paulownia. Based on our experiment, we concluded that growing buckwheat in monoculture significantly increased the number of flowers, resulting in an increase in pollinator density and an increased number of pollinators per unit area.

Landscape crop diversity contributes to higher pollination effectiveness and positively affects rapeseed quality in Mediterranean agricultural landscapes

Pollination is crucial for biodiversity and food security. Heterogeneous agricultural landscapes have a positive effect on pollinator abundance and enhance crop production and quality. In this study, we explored the effects of three landscape features (past crop diversity measured as the Equivalent Richness of crop functional Groups in the previous year [ERGp], semi-natural habitat percentage [SNH], and mean field size [MFS]) and pollinator densities (wild bees [WB] and honey bees [HB]) on pollination and seed quantity and quality in rapeseed crops. Surveying the pollinator density in 20 rapeseed fields revealed a positive relationship with ERGp in the landscape. A pollinator exclusion experiment compared bagged and open-pollinated self-compatible rapeseed plants and revealed insect pollination effectiveness (fruits per flower and number of seeds per pod) and seed quality (oil content). Seed parameters were evaluated in relation to pollinator density (WB-HB) and landscape characteristics. The ERGp emerged as a crucial landscape feature that positively impacted WB density. When insect pollinators were excluded, plants exhibited reduced pollination effectiveness and seed quality. Analysis of open-pollinated plants highlighted ERGp as the most influential variable, positively affecting both sets of parameters. The MFS and SNH showed different but important relationships. Total tocopherol and α-tocopherol were positively correlated with pollinator density in HB, whereas WB showed a positive correlation with γ-tocopherol levels. Increased ERGp positively affected pollinator density and pollination effectiveness, thereby improving oilseed rape production quantity and quality. This study provides new insights into agroecosystem management and pollinator-friendly practices.

Analyzing the relative importance of habitat quantity and quality for boosting pollinator populations in agricultural landscapes.

To increase pollinator populations, international policy targets minimum levels of seminatural habitat cover, but it is unknown whether improving the quality of existing habitats could bring similar benefits without the need of reducing cropland area. Using data we collected in 26 Italian agricultural landscapes during the entire flying season, we explored the relative importance of habitat quantity (seminatural habitat cover) and quality (flower availability) on pollinator densities in seminatural habitats. We obtained transect-based counts and estimated the effect of habitat quantity (proportion of seminatural habitat) and quality (flower cover and richness) on wild bee and hoverfly densities. We used the relationships revealed in the data to simulate pollinator population sizes in landscapes with varying habitat quantity and quality. Wild bee densities were only related to flower availability, whereas hoverfly densities were additionally related to seminatural habitat cover. We found that in complex agricultural landscapes (above 15% seminatural habitat cover), improving habitat quality increased pollinator populations more effectively than increasing habitat quantity. However, increasing habitat quantity was by far the most effective approach for boosting pollinator populations in simple landscapes.

Evaluation of insect pollinator activity on fennel (Foeniculum vulgare) in district Peshawar

The present study was conducted to record the population density of insect pollinators visiting fennel crop at Agricultural Research Institute (ARI), Tarnab, Peshawar during 2020-21. Study was laid out in Randomized Complete Block Design. Data was collected alternate day at two distinct time frames: morning and evening. It was observed that ten insect pollinators visited fennel crop during during the flowering season of fennel crop at mentioned time frames. Total of 10 Species were recorded from the expermintal plots including Apis cerana, A. mellifera, A. dorsata, A. florea, Polistes olivaceus, Earistalis tenax, Eupeodis bacculatus, Pieris brassica, Zizina otis and Coccinella septumpunctata. Order Hymenoptera was the most recorded order or insects with 5 species followed by 2 species each from order Lepidoptera and Diptera while 1 species was reported from order Coleoptera. Highest density of insect pollinators (50.4 and 42.2) in both morning and evening were recorded for A. mellifera whereas the lowest numbers of insect pollinators (3.8 and 2) were recorded for Z. Otis.

The effects of meliponicultural use of Tetragonula laeviceps on other bee pollinators and pollination efficacy of lemon.

The augmentation of pollination success in lemon (Citrus limon Eureka) flowers remains contingent on the involvement of bee pollinators. With wild bee pollinator populations declining in agroecosystems, meliponiculture has emerged as a potential option in Indonesia. This study aimed to investigate the effects of meliponicultural use of Tetragonula laeviceps on diversity, foraging behavior, and monthly population of bee pollinators, as well as lemon pollination efficacy with and without meliponiculture treatment during two periods. Using scan and focal sampling methods in first and second periods, the study found that the diversity of wild bee pollinators was six species (Apis cerana, Lasioglossum albescens, Megachile laticeps, Xylocopa confusa, Xylocopa latipes, and Xylocopa caerulea), and T. laeviceps when using meliponiculture. The relative abundance and daily foraging activity of wild bee pollinators were initially reduced in the first period (March-June) and then maintained in the second period (July-October). T. laeviceps foraged on the flowers, involving specific sequences for 72 s with highest visitation rate of 0.25 flowers/h from 10:00-13:00. Light intensity was observed to be the most influential factor for bee pollinator density. Pollination efficacy results showed that meliponiculture usage has greater benefit compared to meliponiculture absence across various parameters, including fruit sets, fruit weight, yield, and estimated productivity. The effects of meliponicultural use of T. laeviceps can enhance lemon pollination efficacy while preserving the diversity of wild insect pollinators. This suggests that meliponiculture stingless bees could be a beneficial practice in agroecosystems, especially in tropical regions where wild bee populations and diversity are declining.

Factors driving bumble bee (Hymenoptera: Apidae: Bombus) and butterfly (Lepidoptera: Rhopalocera) use of sheared shrubland and young forest communities of the western Great Lakes.

In the northern Great Lakes region, the creation and maintenance of early-successional woody communities as wildlife habitat have increasingly become a conservation priority. The extent to which insect pollinators use these systems remains largely anecdotal. In summer (June-August) of 2021, we surveyed 49 early-successional sites in the western Great Lakes region treated with either shrub-shearing or silviculture (young forest) for bumble bees, butterflies, and habitat components (i.e., structural vegetation and floral resources). Hierarchical distance models predicted pollinator densities (λ^) to be, on average, λ^ = 84 bumble bees/ha and λ^ = 102 butterflies/ha. Although sheared shrubland and young forest communities supported comparable densities of bumble bees and butterflies, density was not equal across all sites. At the microhabitat scale, butterfly density and morphospecies richness were negatively associated with tall shrub cover and butterfly morphospecies richness (but not density) was driven by floral richness. Similarly, bumble bee density was positively associated with metrics of floral resources, underscoring the importance of blooming plants within these woody systems. Landscape covariates explained variation in butterfly density/richness but not bumble bee density. Ultimately, our results demonstrate that blooming plant abundance is an important driver of bumble bee and butterfly densities within these managed early-successional communities. Because early-successional woody communities are dynamic and their herbaceous openings are ephemeral, routine management would ensure that a variety of successional conditions exist on the landscape to meet the needs of bumble bees, butterflies, and potentially other insect pollinators.

Forest conservation maximises açaí palm pollination services and yield in the Brazilian Amazon

Abstract Agricultural expansion is one of the main drivers of global pollinator loss. Paradoxically, this occurs while agriculture is becoming increasingly dependent on biotic pollination, raising concerns about food production. Integrated Crop Pollination (ICP), the use of both wild and managed pollinators in crop fields, can help conserve pollinator diversity while ensuring effective pollination services for growers. However, given the context‐dependent nature of this approach, there is an urgent need to evaluate its application across different landscapes and crops. We apply the ICP approach to açaí palm (Euterpe oleracea Mart.) production in the eastern Brazilian Amazon to explore effects of a native stingless bee, Scaptotrigona aff. postica (Apidae: Meliponini), and landscape‐level forest conservation on yield and socioeconomic outcomes for açaí fruit growers. We assessed flower visitor assemblages and fruit production on 18 plantations across a landscape forest cover gradient, with bee colonies introduced on nine plantations. Field data were combined with information from semistructured interviews of growers to estimate yield and profit per hectare under different pollinator management scenarios. Bee colonies and forest cover enhanced flower visitor abundance on palm inflorescences, but abundance increases attributed to managed bees were associated with shifts in flower visitor evenness and diversity (species richness), due to reduced visitation of wild bees near managed colonies. Fruit production on inflorescences was positively related to bee abundance and bee diversity. Consequently, overall pollination performance was lower in plantations with bee colonies. This was repeated at the hectare scale, where yield and profit were associated with surrounding forest cover and not bee colonies. Synthesis and applications. Managed bees can increase pollinator densities and fruit production, but the increased environmental and socioeconomic risks associated with this activity means açaí growers should prioritise forest conservation to safeguard pollination services and improve overall sustainability of açaí production in the eastern Brazilian Amazon.

Undersowing oats with clovers supports pollinators and suppresses arable weeds without reducing yields

Abstract Sustainable food production requires agriculture to conserve biodiversity and facilitate ecosystem services to maintain productivity levels while reducing inputs detrimental to ecosystem functioning. Increasing within‐field vegetation diversity by legume intercropping seems promising to facilitate cropping system multi‐functionality. Effects of intercropping with legumes on biodiversity‐mediated ecosystem services such as pollination or natural pest control are, however, not sufficiently understood. Using 26 observation plots in a paired field design, we studied the effects of undersowing oats with a mixture of three annual clovers across different aspects of cropping system multi‐functionality. We investigated 16 below‐ and above‐ground ecosystem service indicators related to soil mineral nitrogen, arable weed control, pollination, disease and pest pressures, natural pest control and crop yield. We found lower arable weed cover, higher flower cover and pollinator densities as well as decreased root‐feeding nematode densities in intercropped observation plots compared with the non‐intercropped controls. However, intercropping decreased spider activity densities and oat yield nitrogen content. Root diseases, pest damages, natural pest control and crop yield were not affected by intercropping. The biomass of undersown clovers was positively related with the differences in flower cover and pollinator densities, and negatively related with the differences in arable weed cover between the intercropped and the control treatment. Synthesis and applications: We demonstrate that undersowing annual clovers suppresses arable weeds and simultaneously support pollinators without reducing crop yields or taking land out of arable production. Undersown plant mixtures should, however, be tailored to support a wider spectrum of pollinators and benefit natural pest control to support a higher level of overall cropping system multi‐functionality.

Demographic study of a peripheral population of the rare amphicarpic species Scrophularia arguta

Scrophularia arguta (Scrophulariaceae) is a rare amphicarpic annual species with a fragmented distribution in North Africa, part of the Arabian Peninsula, and Macaronesia, with several peripheral populations on the Iberian Peninsula (south-western Europe) as well. The Iberian populations have a disjunct distribution: several endangered or critically endangered populations are present in the southeast versus a few non-listed ones representing a relict lineage with a unique plastid haplotype inhabiting the west-central region (Extremadura). In this study, we examined the largest and most important population of this relict lineage to assess potential threats to its survival. We evaluated pollination and reproductive systems, floral rewards, fruit and seed set from chasmogamous and cleistogamous flowers, and population dynamics (i.e., phenology, survival, reproductive success, and predation level). We found that the main threats to the population are predation by wild herbivores, such as red deer and, to a lesser extent, Cucullia scrophulariae caterpillars. These threats decrease reproductive success to such an extent that population survival may be in jeopardy if no action is taken to reduce the effects of herbivores. In addition, the existence of nearby beehives alters the presence and density of wild pollinators that contribute to gene flow via pollen transfer and increase genetic variability. Cleistogamous seeds may help maintain the population in specific microhabitats (mainly quartzite rock cracks), although at the cost of reducing genetic variability. Finally, we recommend that regional/national administrations responsible for biodiversity matters adopt measures to ensure the conservation and survival of west-central populations. Scrophularia arguta predation by vertebrates. Left, group of several individuals before and after vertebrate predation. Right, vertebrate predation level. • Wild vertebrates and caterpillars threaten a relict Scrophularia arguta population. • Managed honeybees displace natural pollinators. • The conflict between plant and animal conservation requires monitoring. • The action of regional/national administrations is needed to conserve this species.

Limited honeybee hive placement balances the trade-off between biodiversity conservation and crop yield of buckwheat cultivation

An increasing number of farmland initiatives aim to aid biodiversity conservation through alternative farming practices such as nature-inclusive farming. However, these approaches frequently lead to trade-offs between biodiversity conservation and crop yield. For example, buckwheat (Fagopyrum esculentum) is a melliferous crop that flowers for a long period in the summer when nectar in agricultural areas is generally scarce, and buckwheat cultivation could therefore contribute to wild pollinator conservation. However, honeybees (Apis mellifera) are placed to ensure sufficient crop pollination, which potentially increases resource competition with wild pollinators in and around the crop. Here, we have studied this trade-off by surveying pollinators in and around 16 small-scale (∼1 ha) flowering buckwheat fields and we determined the contribution of pollinator density to crop yield in a nature-inclusive farming project. We found that the buckwheat pollinator community was diverse, albeit dominated by honeybees. We found no clear indications of resource competition between honeybees and wild pollinators within the buckwheat fields. Honeybee density in the surroundings was generally low, and increased minimally during honeybee-hive placement. While densities of honeybees decreased non-linearly over the day in buckwheat fields, they did not (temporarily) move into the surroundings of the field, suggesting limited competition for resources with wild pollinators. Crop yield was largely dependent on crop pollinator density, notably of honeybees, and to a lesser extent crop biomass (as a proxy for agricultural management). Our results show that buckwheat cultivation fits well within nature-inclusive farming if some simple precautionary measures are being taken, such as limiting the honeybee-hive densities and placing hives only during the main flowering period. The introduction of buckwheat cultivation into crop rotation could then contribute to fill an important nectar gap in the summer, which potentially boosts wild pollinator populations in the long term.

Native Flowering Border Crops Attract High Pollinator Abundance and Diversity, Providing Growers the Opportunity to Enhance Pollination Services.

Over the past century, habitat loss from agricultural intensification has contributed to pollinator decline. One way to mitigate the harmful effects of agricultural intensification is through the re-introduction of native flowering plants as border strips that provide supplemental floral and nesting resources to pollinators. However, border crop species vary in bloom period and flower densities, and are thus likely to attract different suites of pollinator species. Resulting differences in pollinator community composition are likely to affect their ability to provide pollination services to adjacent crop habitat. To address these issues, we implemented a two-year study on the impact of different flowering border crops on pollinator abundance, richness, and community composition. We also examined which crop features (bloom duration, number of flowers, floral area) were most likely to affect pollinator densities. We found that native flowering plant border crops of diverse prairie mix and monocultures of silflower (Silphium integrifolium Michx.) and cup plant (Silphium perfoliatum L.) attracted the highest abundance and species richness of bees and pollinator groups combined, while alfalfa (Medicago sativa L.) attracted the highest lepidopteran abundance and species richness. We also found a significant, positive relationship between pollinator abundance and floral resource amount and bloom duration. These findings offer valuable insight into the impacts of different land management strategies on different pollinator groups, and thus provide landowners with management options for attracting specific pollinator groups and species.

Landscape composition modifies pollinator densities, foraging behavior and yield formation in faba beans

Wildlife-friendly management practices promote pollinators and pollination services in agricultural landscapes. Wild bee densities are driven by landscape composition, as they benefit from an increased availability of nesting and foraging resources at landscape scale. However, effects of landscape composition on bee foraging decisions and consequences for crop pollination have rarely been studied. We investigated, how landscape composition affects bee densities and foraging behavior in faba bean (Vicia faba L.) fields and how this impacts faba bean yield. We recorded densities and nectar robbing behavior of honeybees, long- tongued and short-tongued bumblebees in faba bean fields in eleven landscapes with varying landscape composition (e.g. land cover of oilseed rape, faba bean and semi-natural habitats). Moreover, we assessed yield components of faba beans via pollinator exclusion experiments. Increasing covers of faba bean and semi-natural habitats positively influenced bumblebee densities, while high oilseed rape covers negatively affected short-tongued bumblebee densities in bean fields. Increased faba bean covers enhanced the proportion of nectar-robbing short-tongued bumblebees. The number of beans per pod was increased by insect pollination, while the number of pods was decreased; these effects however depended on variety. Landscape composition interacted with bee densities in shaping yield components in V. faba. Our study emphasizes the importance of considering landscape management to maximize crop yields, as shown for the case of faba beans. The composition of agricultural landscape can modulate bee densities in crop fields, bees foraging behavior and pollination services.

Importance of maternal resources in pollen limitation studies with pollinator gradients: A case study with sunflower

Pollen limitation studies are scarce in entomophilous crops, as it can be very tedious to supplement plants with hand pollination at the relevant plant scale. To overcome this, recent studies have used pollinator gradients over several fields to assess whether crops were pollen limited. But the plant maternal resources and thus the yield potential may vary between fields of the same crop. If these resources are not properly controlled, it may affect the conclusions of the study.We investigated the relationship between yield, measured as seed number, seed mass, and seed oil content per head, and pollinator density in sunflower (Helianthus annuus L.) by using a gradient of pollinator densities set both across and within fields. We analyzed the yield and the % of yield potential, the latter being assessed with pollen supplementations applied at the whole plant scale. We analyzed the data both with and without random effects including year, cultivar, field and sampling plot. We also compared the yields of open and pollen-supplemented sunflowers to sunflowers isolated under tulle bags to assess autonomous self-fertilization and self-production rates in each field.Without random effects included in models, yields increased with pollinator density but only up to 0.3 bees per head, implying pollen limitation only below this threshold, while with random effects included, the yields were marginally pollen limited across the whole range of pollinator densities observed (P = 0.072 and 0.037). Yet, on the other hand, there was no relationship between bee density and % of yield potential (assessed with pollen supplementation treatments), with or without random effects included, implying no pollen limitation across the complete range of bee densities observed in our study (0.1–1 bees per sunflower head). These last results are explained by variation in the yield potential between and within fields, and by the positive correlation found between yield potential and pollinator density. Insect pollination contributed on average to 53.7% and 42.8% of the seed number and mass per head, respectively, and also increased the seed oil content by 5.5% on average.Our study showed that plant maternal resources and random effects are crucial to consider when quantifying pollen limitation using pollinator gradients and yields. Pollinator gradients on a per flower basis are a useful tool to identify target pollinator densities to maximize yields, but should be combined with pollen supplementation treatments at the relevant scale in order to correctly assess pollen limitation.

Annual flower strips and honeybee hive supplementation differently affect arthropod guilds and ecosystem services in a mass-flowering crop

Intensively managed agricultural landscapes have degraded the provisioning of diverse and continuous forage and shelter habitats for arthropods and weakened the delivery of ecosystem services such as insect crop pollination and biological pest control. In response, farmers are incentivised to sow flower strips along field margins to counteract resource bottlenecks. Yet, it is poorly understood how effective this diversification practice is when combined with the supplementation of honeybee (Apis mellifera L.) hives, which is commonly used to boost insect pollination in flowering crops. Honeybees share floral resources with wild pollinators and natural enemies of pests, which could lead to competition for food resources. We sampled pollinators, natural enemies and their pests as well as estimated the benefit of insect pollination in 17 organic faba bean (Vicia faba minor L.) fields in southern Sweden either with or without sown annual flower strips and with or without added honeybee hives. In fields with flower strips, bumblebee (Bombus spp.) densities were redistributed from field edges to interiors but without affecting their overall densities. Flower strips enhanced silver Y moth (Autographa gamma L.) densities and carabid beetle Shannon diversity along the field edge, and overall spider activity density. The supplementation of honeybee hives enhanced honeybee densities, overall ladybird beetle densities, black bean aphid (Aphis fabae Scop.) densities along field edges, but deterred silver Y moths and pushed bumblebees towards the field interior. Bean mass per plant was higher in insect pollinated plants compared with bagged, self-pollinated plants. This insect pollination benefit was independent of honeybee hive supplementation and the flower strip treatment suggesting that faba bean fields were not deficient in pollinator visits. We conclude that flower strips did not provide sufficient floral resources to increase overall wild pollinator densities in faba bean fields. Yet, annual flower strips attracted and facilitated ground-dwelling predators, especially spiders, to faba bean fields, likely by providing beneficial shelter habitats. It is worth noting that 2018, in which we collected our data, was characterised by late frosts in spring followed by an unusually hot and dry summer. While these unforeseen weather conditions together with a relatively small sample size might limit the generalisation of our results, we argue that conducting experiments under such conditions provide insights into the effectiveness of agri-environmental schemes under climate change, especially considering that such weather conditions are becoming increasingly more frequent.

DOES CLEISTOGAMOUS SELF-FERTILIZATION PROVIDE REPRODUCTIVE ASSURANCE AGAINST SEED PREDATION IN RUELLIA HUMILIS?

Mixed mating is thought to be adaptive in many species of flowering plants because self-fertilization provides reproductive assurance when pollinator densities are low. In species with dimorphic flowers, automatic self-fertilization by small cleistogamous (CL) flowers might also provide reproductive assurance by avoiding floral herbivory. We tested this hypothesis by quantifying flower production, seed production, and seed predation across an entire reproductive season within a Missouri population of Ruellia humilis, a species with mixed mating enforced by dimorphic flowers. The production of CL flowers was delayed relative to the production of open-pollinated chasmogamous (CH) flowers, consistent with the hypothesis of reproductive assurance. The rate of seed predation by larvae of the Noctuid moth Tripudia rectangula was much higher for fruits produced by CH flowers (69%) than by CL flowers (18%). Thus, although CH flowers self-pollinate in the absence of outcross pollen, CL flowers are a much more economical source of selfed seeds, not only because they require fewer resources but also because they experience much lower levels of seed predation. Seed predation by Tripudia is common in many other cleistogamous species of Ruellia native to the southern United States and Mexico and might have played a significant role in the evolution of CL flowers in this large genus.

Modelling the effects of the repellent scent marks of pollinators on their foraging efficiency and the plant-pollinator community.

Pollinator insects forage in complex and unpredictable resource landscapes, often using social information from congeneric individuals to acquire knowledge about their environment. It has long been recognized that this process allows them to exploit floral resources more efficiently and thus increase individual fitness. However, by creating correlations between the behaviors of pollinators within a population, this could also indirectly influence the entire plant-pollinator community. One type of social information used by pollinators is the scent mark left on the corolla of flowers by previous visitors, which can be used as a cue to avoid recently depleted resources. We developed a spatially explicit agent-based model to examine the effects, at both individual and community levels, of pollinators using these scent marks. The model simulates a population of pollinators foraging on flowers in a continuous 2D space in which we can vary the density of pollinators. We showed that the use of scent marks as a source of information significantly increased the foraging efficiency of pollinators except when competition between pollinators was very low. At the community level, this also resulted in a marked homogenization between floral resources within the landscape: in the absence of scent marks, the coefficient of variation of the remaining nectar quantity per flower strongly increased with greater pollinator competition, but it remained low at all levels of competition when scent marks were used by the pollinators. Finally, the use of scent marks markedly decreased the number of pollinator flower visits, especially at high levels of pollinator competition, which can potentially reduce the pollination service.

High population density of bee pollinators increasing Camelina sativa (L.) Crantz seed yield: Implications on the potential risk for insect-mediated gene flow

New Camelina sativa genotypes have been genetically engineered (GE) to produce unique high-value chemical compounds and biofuel products. However, baseline information on predictive environmental risk assessment on this plant is urgently needed to establish guidelines for commercial large-scale production. Pollinating insects such as bees could facilitate the spread of transgenes into the ecosystem and raises ecological concerns on insect-mediated gene flow. Thus determination of the potential impact of pollinating insects on C. sativa pollination and gene flow becomes important. A 4-year experiment conducted in Connecticut, USA (2017) and Yangzhou, China (2019–2021) was carried out to determine the pollination effect of different densities of honey bees (Apis mellifera L.) populations on C. sativa seed yield and assess their involvement on C. sativa pollen dispersal. Insect cages experiments with presence or absence of honey bees showed that C. sativa seed yield was not affected by a relatively low population density of honey bees (20 honey bees m−2). However, at a higher density of honey bee population, Camelina sativa seed yield (0.23 g plant-1 and 73.3 g m−2) was statistically greater than those of the uncaged control (0.21 g plant-1 and 68.9 g m−2), caged C. sativa plants without honey bees (0.20 g plant-1 and 66.3 g m−2) or with 20 honey bees m−2 (0.21 g plant-1 and 66.9 g m−2), although C. sativa is commonly assumed to be self-pollinated. Principle coordinate analysis (PCoA) made from SSR markers revealed that honey bee and bumble bee are able to transfer C. sativa pollen from pollen source to adjacent flowers of other species (e.g., Brassica juncea, Brassica napus) up to 10−15 m beyond the field edge, raising ecological concerns on insect-mediated gene flow between adjacent C. sativa fields particularly if GE C. sativa cultivars are involved. The new information in this study will help to better understand C. sativa pollination biology, environmental risks associated with insect-mediated gene flow, and develop management strategies to reduce gene flow and facilitate coexistence between GE and non-GE C. sativa under natural agroecosystem.