Changes in the Relative Abundance and Movement of Insect Pollinators During the Flowering Cycle of Brassica rapa Crops: Implications for Gene Flow (original) (raw)
Related papers
2009
The overall aim of the study was to assess the risk of gene flow from Brassica crops by insectmediated pollen transport. I measured the viability of pollen in Brassica flowers throughout crop development and compared this with the viability of pollen transported by insects inside and outside one early- and one late-season crop. In order to evaluate the relative importance of different species in pollen transport, I measured abundance of flower visitors during crop development, and measured the foraging behaviour of five key pollinator species throughout the growing season, in relation to variation in microclimate, crop phenology and the relative abundance of other pollinator species competing for flower resources. Flower visiting insects of Brassica rapa crops were highly diverse, and their abundance and diversity changed with crop phenology. I found similar abundances at the family level for both crops studied, although capture rates were greater in the early- than in the late-seas...
Spatial scale of insect-mediated pollen dispersal in oilseed rape in an open agricultural landscape
Journal of Applied Ecology, 2011
1. Interest in pollen-borne gene dispersal has grown with the cultivation of genetically modified plants. To date, both experimental data and models of oilseed rape (OSR) Brassica napus pollen movement at the landscape scale do not clearly differentiate between wind-and insect-mediated dispersal. Estimations of insect-mediated gene dispersal would be valuable for managing potential escapes of transgenes. 2. To quantify the intensity and spatial scale of pollen dispersal by insect pollinators in an agricultural landscape, bait points made of flowering male-sterile OSR that attract OSR pollinators were located at six distances (10-1100 m) from the closest OSR fields and feral populations. Flower-visiting insects were caught by net on these male-sterile flowers and were rubbed onto the stigmas of male-sterile OSR plants grown in a pollen-proof greenhouse to do a manual pollination of their flowers. In this way we were able to assess the insects' OSR pollen load and seed production at each of the six distances. 3. A large diversity of insects carried OSR pollen and contributed to seed production, but not pollen beetles Meligethes aeneus. Logistic regression analyses of the seed-set success from the manual pollination demonstrated that seed set significantly increased with the proximity of OSR fields, the size of the pollinating insect, and the main daily temperature. Seed set was not affected by the pollinating insect's order or genus. Seed set, both observed and predicted by the model, was above zero for flowers pollinated with large bees caught at >1100 m from the nearest OSR field. 4. Synthesis and applications. Our study provides clear evidence that a large variety of insect species can transfer viable pollen between OSR plants over considerable distances. However, only 39AE4% of the insects caught on male-sterile flowers carried OSR pollen. Our results provide valuable data to improve models of pollen dispersal for entomophilous crops at the landscape scale. These models are essential to help land-managers reduce pollen-borne gene dispersal from genetically modified plants to wild and cultivated relatives.
PeerJ, 2014
Background. Up to 75% of crop species benefit at least to some degree from animal pollination for fruit or seed set and yield. However, basic information on the level of pollinator dependence and pollinator contribution to yield is lacking for many crops. Even less is known about how insect pollination affects crop quality. Given that habitat loss and agricultural intensification are known to decrease pollinator richness and abundance, there is a need to assess the consequences for different components of crop production. Methods. We used pollination exclusion on flowers or inflorescences on a whole plant basis to assess the contribution of insect pollination to crop yield and quality in four flowering crops (spring oilseed rape, field bean, strawberry, and buckwheat) located in four regions of Europe. For each crop, we recorded abundance and species richness of flower visiting insects in ten fields located along a gradient from simple to heterogeneous landscapes. Results. Insect po...
Proceedings. Biological sciences / The Royal Society, 2015
The transfer of genes between populations is increasingly important in a world where pollinators are declining, plant and animal populations are increasingly fragmented and climate change is forcing shifts in distribution. The distances that pollen can be transported by small insects are impressive, as is the extensive gene flow between their own populations. We compared the relative ease by which small insects introduce genetic markers into their own and host-plant populations. Gene flow via seeds and pollen between populations of an Asian fig species were evaluated using cpDNA and nuclear DNA markers, and between-population gene flow of its pollinator fig wasp was determined using microsatellites. This insect is the tree's only pollinator locally, and only reproduces in its figs. The plant's pollen-to-seed dispersal ratio was 9.183-9.437, smaller than that recorded for other Ficus. The relative effectiveness of the pollinator at introducing markers into its own populations...
Mechanisms of pollination : quantifying insect and plant contributions
2018
Global agricultural production is reliant on insect-mediated pollination, which is largely provided by the European honey bee (Apis mellifera L.). Recent concern about the health of honey bees has raised significant concern about the future of food production and, as a result, alternate pollinators have been explored to provide these services. However, identifying which insect species are efficient pollinators of a particular plant species is challenging and labor-intensive. Additionally, even if an alternate pollinator is identified, its services may be insufficient to prevent pollination failure, which may be due to other factors. This thesis explores different measures that can be used to assess a species' effectiveness as a pollinator and the causes of pollination failure. Particularly, it addresses four main questions: 1) whether insect behavior or pollen transport can be used to predict single-visit pollen deposition (and thus pollinator efficiency) in four vegetable seed ...
Linking pollinator occurrence in field margins to pollinator visitation to a mass-flowering crop
Journal of Pollination Ecology, 2021
Uncultivated field margins are important refugia for pollinating insects in agricultural landscapes. However, the spill-over of pollination services from field margins to adjacent crops is poorly understood. This study (i) examined the effects of landscape heterogeneity on pollinator occurrence in permanent field margins and pollinator visitation to adjacent mass-flowering turnip rape (Brassica rapa ssp. oleifera) in boreal agricultural landscapes, and (ii) tested whether pollinator abundance and species richness in field margins predict abundance and species richness of crop visitors. Pollinators visiting the crop were more affected by landscape heterogeneity than pollinators in adjacent margins. Species richness, total abundance, and the abundance of syrphid flies visiting the crop increased with increasing landscape heterogeneity, whereas, in field margins, landscape heterogeneity had little effect on pollinators. In field-dominated homogeneous landscapes, wild pollinators rarely...
Insect pollination enhances yield stability in two pollinator-dependent crops
Agriculture, Ecosystems & Environment, 2021
One of the most important challenges facing global agriculture is to ensure an adequate, stable food supply while conserving soil, water and biodiversity. The yield stability of pollinator-dependent crops, such as pear and apple, can be negatively affected by variability of the pollination service, which in turn can reduce mean yield. We explored how mean crop yield and yield variability were affected by pollinators and variability in their provision of the pollination service. Over four seasons we conducted a manipulative experiment in six pear and eight apple farms; fruit set (i.e., no. fruits/ no. flowers) was compared between flowers exposed to pollinators and those excluded from pollinators. We also recorded pollinator visitation rate to exposed flowers. We estimated the mean levels and spatial and temporal variability of both pollinator visitation and yield response by calculating the mean values per farm and the spatial (i.e., across trees within farm) and temporal (i.e., across seasons within farm) coefficients of variation (CV) for visitation rate and fruit set. Despite homogeneous irrigation and fertilization, we found strong variability in fruit set in both crops (pear spatial and temporal CV: 0.57 and 0.4, respectively; apple: 0.62 and 0.52). Pollinator exclusion reduced mean fruit set considerably in both crops (pears: a reduction of 50%, apples: 71-92%), and increased spatial and temporal variability (pears: 296% and 197% for spatial and temporal variability, respectively; apples: 385% and 329%). Visitation rates in pears were positively associated with mean fruit set and negatively related to its spatial CV. Also, in this crop we found a positive relation between the spatial CV of visitation rate and fruit set. However, there was no evidence that visitation rate in open-pollinated apple flowers affected either mean fruit set or its spatial or temporal variability. Apple trees received one order of magnitude more visits per flower than pear trees, suggesting that in this system the pollination service meets the pollination demand of the apple crop. Overall, our results highlight the importance of management practices that prioritize pollination service, thus ensuring a high, stable yield.
Journal of Applied Ecology, 2012
1. Recent declines in honeybee populations have focused attention on the potential for unmanaged insects to replace them as pollinators of food crops. The capacity of unmanaged pollinators to replace services currently provided by honeybees depends on the spatial and temporal variability of these services, but few quantitative assessments currently exist. 2. We investigated spatial variation in pollinator importance by comparing pollinator efficiency and effectiveness in stigmatic pollen loads, stigmatic contact and visitation rate between honeybees and the seven most abundant unmanaged taxa in 2007. We assessed temporal variability in pollinator visitation using floral visits recorded three times a day over four consecutive years (2005)(2006)(2007)(2008) in 43 'Pak Choi' Brassica rapa ssp. chinensis mass flowering fields in the Canterbury region of New Zealand. Further, we compared the aggregate effect of the unmanaged pollinator assemblage to the managed honeybee. 3. Pak Choi was visited by many insect species that vary in abundance and effectiveness as pollen transfer agents. There was spatial variation in the four measures of pollinator importance. Pollen deposited on stigmas and flower visits per minute were not significantly different comparing the unmanaged assemblage to honeybees, although stigmatic contact and visitor abundance per number of open flowers were greater in honeybees. 4. Unmanaged taxa were frequent visitors to the crop in all 4 years. The pooled services provided by the unmanaged assemblage did not differ within a day and were equal to or greater than those provided by honeybees in 2 of the 4 years. Pollinator importance changed little irrespective of the spatial and temporal variations among taxa. 5. Synthesis and applications. The results of this study suggest that some unmanaged insect taxa are capable of providing consistent pollination services over a 4-year period in a commercial mass flowering crop. As these taxa already contribute substantially to the pollination of food crops, they offer a safety net in the case of sudden collapse of managed honeybee hives. To optimize pollination services, we recommend pollinator-specific farm management practices that consider the needs of both managed and unmanaged pollinator taxa.
Landscape Ecology
Context Maximising insect pollination of mass-flowering crops is a widely-discussed approach to sustainable agriculture. Management actions can target landscape-scale semi-natural habitat, cropping patterns or field-scale features, but little is known about their relative effectiveness. Objective To test how landscape composition (area of mass-flowering crops and semi-natural habitat) and field-scale habitat (margins and hedges) affect pollinator species richness, abundance, and pollen deposition within crop fields. Methods We surveyed all flower visitors (Diptera, Coleoptera and Hymenoptera) in oilseed rape fields and related them to landscape composition and field features. Flower visitors were classified as bees, non-bee pollinators and brassica specialists. Total pollen deposition by individual taxa was estimated using single visit pollen deposition on stigmas combined with insect abundance. Results The area of mass-flowering crop had a negative effect on the species richness an...