Q&A: Jane Stout
Jane Stout and the Trinity research team proved for the first time in Ireland that foraging insects boost crop yield.
When researchers from Trinity College Dublin excluded pollinating insects from oilseed rape flowers, there was a 27% decrease in the number of seeds produced, and a 30% decrease in seed weight per pod (in winter crops).
It’s the first time researchers here were able to show that foraging insects which transfer pollen from flower to flower greatly boost crop yield.
For winter oilseed rape crops alone, they have calculated that the economic value of insect pollination is €2.6m per annum. And there’s an extra €1.3m worth of extra yield in spring oilseed rape, due to insect pollination.
Associate professor in botany and director of the Trinity Centre for Biodiversity Research, Jane Stout, who was the principal researcher, said: “Oilseed rape fields are full of pollinators, including honeybees, bumblebees, solitary bees and hoverflies.”
¦ Your research findings indicate a decrease in insect numbers could reduce crop yields. How can farmers help to ensure continued adequate provision of pollination services by honeybees and wild pollinators to crops such as oilseed rape?
>> Beekeepers often place hives near flowering oilseed rape fields, which results in a lot of honeybees visiting the crop and pollinating flowers. For covered crops, such as strawberries, farmers can buy in bumblebee nests to place in glasshouses, but the bees often escape. They can then spread disease to wild bees, or become established in the wild themselves. The alternative is to support wild pollinators in farmland all year round, and then they will do the job when field and orchard crops flower. These insects need flowers for food, places to nest, over-winter, and mate. Farmers can provide these by encouraging wildflowers, or planting nectar and pollen seed mixes in strips or uncropped areas, to provide forage throughout the season, and by maintaining hedgerows to have a mix of woody and herbaceous flowering plants, to provide food and places to nest. Avoiding the use of pesticides on non-cropped areas helps provide nesting and foraging resources, while using pesticides on crops only when they are needed also helps.
¦ Farmers know there are much fewer pollinating insects around now. How real is the threat in Ireland to these insects?
>> Like many other species, pollinating insects are in decline worldwide. This is primarily driven by habitat loss, pesticides and diseases, as well as climate change, invasive alien species, and pollution. These same threats exist in Ireland, where changes in agricultural practices such as more silage cutting, fewer hay meadows, increased use of agrochemicals, and a loss of hedgerows all threaten pollinators. Some of our species, like the great yellow bumblebee, are on the verge of extinction. Even formerly common species have become rare.
¦ Neo-nicotinoid pesticides are implicated in declines of many pollinator species. How effective will the EU ban on use of these pesticides be?
>> It’s hard to say, but there is a lot of research going on at the moment to try to answer that question. Three neo-nicotinoids (imidacloprid, clothianidin, and thiamethoxam) have been banned as seed treatments, for soil application and foliar treatment in crops attractive to bees. This is good news, as scientific evidence shows they negatively affect insect behaviour and reproductive success, as well as their ability to resist disease. However, these chemicals are still used for crops that are not attractive to bees, and are persistent in agricultural irrigation channels and soil.
Thus, they may still get into the nectar and pollen of both crop and wild plants, despite the ban. This also means it is very hard to test whether the ban will have any positive effect on the bees, because these chemicals are so common in the environment. Additionally, farmers may switch to using other, equally harmful chemicals.
¦ What insects, in what quantities, did you find are important pollinators of oilseed rape crops? >>
We found 26 species in winter oilseed rape fields in south-east Ireland, including the honeybee, five bumblebee species, eight solitary bee species and 12 hoverfly species. There are probably more — these are just the ones we saw in our 2009 and 2010 surveys. The most common flower visitors were bumblebees, honeybees, and the drone fly (a hoverfly which mimics male honeybees). The honeybees carried the most pollen grains on their bodies.
¦ Why did you choose oilseed rape for research on pollination? >>
It is one of the most economically important insect-pollinated field crops grown in Ireland, and production has increased massively over the past few years due to the heightened demand for seed oil. Other important insect-pollinated crops in Ireland include apples, strawberries and other soft fruits, field beans, peas, and clover, which is increasingly used in pastures.
¦ What was the technique used to exclude pollinating insects from oilseed rape flowers, for your research purposes? >>
Flower heads were bagged prior to flowers opening, using tulle netting (with a 1.2mm diameter mesh). This stopped insect pollinators from accessing flowers, but still allowed wind pollination. Bags were removed when the flowers had finished flowering, to allow continued plant growth. This is a standard technique used in crop research worldwide.
¦ Why did you pursue this research?
>> This research was part of a larger project sponsored by the Environmental Protection Agency, which asked how human activity in a range of sectors affects biodiversity and ecosystem services. One of the sectors we assessed was the increased area of crops grown for bioenergy. Since oilseed rape is used for biodiesel, we studied the effects of oilseed rape cultivation on farmland wildlife, including pollinators. We also found that a wide range of pollinating insects use bioenergy fields (not just oilseed rape but also miscanthus).
¦ Why should we conserve pollinators in Ireland? >>
They are important for crop pollination, and we can make estimates of how yield and income may be affected by pollinators, as we did with oilseed rape. However, it’s not just that they pollinate crops. We often forget the critical pollination job they do for wild plants, and the positive effects they have on the rest of the ecosystem. Many wild plants only produce fruits and seeds when they are pollinated by insects, and these fruits provide food for farmland birds and other animals. In addition, these plants are important for ecosystems in terms of carbon sequestration, oxygen production, nitrogen fixation, and soil erosion protection. So, conservation of pollinators results in maintenance of healthy ecosystems that are fundamental to human wellbeing.
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