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New research reveals groundbreaking pollination insights for apple growers

Research & Extension

Authors: Dr Katja Hogendoorn, Dr Scott Groom, Romina Rader, Dr Julian Brown, Tanya Latty, Yolanda Hanusch – AgriFutures Australia.

This article originally appeared in the Winter 2021 edition of AFG.

Key findings

  • Honey bees play a major role in crop pollination in apple orchards
  • Landscape surrounding apple orchards influences the presence of feral honey bees and native pollinators, translating to increased apple quality
  • Supporting diverse pollinator communities through supportive landscape and sustainable production practices may help secure fruit quality
  • Open grassland near apple orchards enhances crop visitation by native bees
  • Run an online simulation of how native vegetation can improve pollination on your farm.

Australian-first research has delivered breakthrough findings for the apple industry to help growers enhance pollination security and ultimately, productivity.

The project, Securing Pollination for more Productive Agriculture: Guidelines for effective pollinator management and stakeholder adoption, delivered as part of the Australian Government Department of Agriculture, Water and the Environment Rural R&D for Profit program, saw collaboration between Australia’s most knowledgeable bee and pollination researchers from the University of Adelaide (UoA), Australian National University (ANU), University of New England (UNE) and University of Sydney (USYD), from June 2016 to February 2021.

Researchers assessed the contribution of pollinators to nine Australian crops including apples, to allow growers to implement evidence-based management strategies to support crop pollinators.

Crop pollinators contribute about $14 billion to the Australian economy annually, with the produce that depends on pollination including 35 species of fruit, vegetables, nuts, cotton, as well as oil and pasture seeds.

Safeguarding pollination serves the interest of both the growers and consumers of pollination dependent crops.

Role of feral honey bees

While most apple growers lease hives for pollination, there are a range of insects providing free pollination services in orchards throughout Australia.

Researchers found feral honey bees play a major role in crop pollination, particularly in apple orchards.

Dr Katja Hogendoorn, lead researcher at University of Adelaide, said for apples, landscape surrounding the crop influences the presence of feral honey bees and native pollinators, translating to increased apple quality.

“In apple orchards, we found correlations between open grassy land and visitation by native halictid bees. The number of empty carpels decreased with increased native pollinator visitation, which increases apple symmetry and quality,” Dr Hogendoorn said.

“Our conclusions correspond with findings throughout the world regarding the effects of native woody vegetation and grasslands on visitors, as well as the order of magnitude of yield increases as a result of the presence of beneficial vegetation.”

Who is visiting your apple orchards?

Native bees including reed bees (pictured), furrow bees and slender furrow bees were among those adding diversity to pollinators in southern regions.

Although apple was a major focus, the team looked at a number of crops. There was a wide range of insect visitors to the crop, which varied between crop species, years and locations. Numbers and species of bees also varied between crops, regions and years. The team has put together a free online guide that lists the pollinators across all crops studied.

Insects visiting apple flowers were observed and collected by researchers at 14 sites across the Adelaide Hills production area in South Australia; nine sites in Stanthorpe, Queensland; six sites in the Yarra Valley, Victoria; and six in Tasmania’s Huon Valley.

While researchers found honey bees were the most abundant species in all regions, other insect species accounted for nearly 40 per cent of recorded visitors in some orchards.

In Stanthorpe, where orchards are commonly protected by hail-netting, another key researcher Associate Professor Romina Rader, University of New England found that visitors other than honey bees were relatively rare, while stingless bees (Tetragonula) and carpenter bees (Xylocopa) were part of the mix in other crops such as blueberry.

Apple orchards surveyed in the Adelaide Hills, Huon Valley and Yarra Valley were predominantly unnetted and had a higher diversity and abundance of visitors.

For example, in the Yarra Valley, Australian National University’s Dr Julian Brown found that native apple visitors were predominantly twig nesting reed bees (Exoneura), followed by furrow bees Lasioglossum (Chilalictus).

In Tasmania, Associate Professors Tanya Latty and Yolanda Hanusch from the University of Sydney, discovered that honey bees made up the vast majority of visitors, accounting for 90 per cent of visits. Hoverflies (Syrphinae spp) and reed bees (Exoneura spp) were the next most common, representing 2 per cent and 3 per cent of visitors, respectively.

Finally, In the Adelaide Hills, furrow bees (Lasioglossum) and slender furrow bees (Homalictus) were the most diverse and abundant group after honey bees, making up between 2–35 per cent of visitors, depending on the orchard. Nest entrances of these ground-nesting bees were sometimes seen in the soil beneath apple trees, in particular in headlands where herbicide was applied, which suggests that supporting their population with alternative floral resources before or after crop flowering could benefit apple pollination.

Overall, >30 species of insects visited flowering apple– including beetles, wasps, butterflies and moths, two hoverflies (Eristalinae sp. and Syrphinae sp.), muscid and blowflies and 15 native bee species (Apis mellifera, Bombus terrestris, Exoneura sp, Leioproctus sp., two Homalictus species and eight species of Lassioglossum).

The furrow bee L. (C.) lanarium is particularly widespread and occurs in nearly all production areas and crops in south-eastern Australia, making them a suitable target for management strategies that support their role as crop pollinators.

Figure 1. While researchers found honey bees were the most abundant species in all regions, other insect species accounted for nearly 40 per cent of recorded visitors in some orchards.

Crop pollination effectiveness

Pollination effectiveness of a visiting species depends how abundant the visitors are on the flowers and how much suitable pollen they deposit onto the stigma per visit.

Suitable pollen is pollen that will grow a pollen tube and result in fertilisation, and hence seed and fruit production. In apples, cross pollination with pollen from a different variety is needed to achieve fruit set.

Collaborators from UNE found that, per flower, more than 10 visits by honey bees were required to achieve 100 per cent fruit set in Stanthorpe apple orchards.

Impacts on crop productivity

After finding that open grassland near apple orchards enhanced crop visitation by insects, researchers went a step further and looked at impacts on productivity.

Apple growers initially aim for good set, but then thin the crop as they aim to maximise quality over quantity. A top-quality apple has high colour, no blemishes, is not too large or small, and is symmetrical.

Of these quality aspects, pollination influences only symmetry, which is driven by even seed set in all carpels and is achieved by sufficient visitation of the apple flowers.

In addition to assessing the link between native vegetation and pollinator presence and abundance, researchers also looked at whether increased pollinator diversity and abundance would translate into increased quality of the resulting fruit.

In three Australian apple production areas – Stanthorpe, Yarra Valley and Adelaide Hills – researchers assessed the number of floral visitors to apple flowers (per 100 flowers per hour).

Dr Julian Brown, a project contributor ANU, said orchards in Stanthorpe had a significantly higher honey bee visitation than the Adelaide Hills and Yarra Valley.

“It is likely that this is caused by the fact that managed honey bee hives were placed under netting,” he said.

“We expected netting to have a strong negative effect on other flower visitors, but this was only borne out for native bees. The hourly native bee visits per 100 flowers was significantly greater in the Yarra Valley. Overall, only in Stanthorpe were visitation rates sufficient to surpass the recommended target rate of 55 visit per 100 flowers per hour.”

Dr Scott Groom, University of Adelaide examined how pollinator visitation relates to crop quality by examining the number of seeds and symmetry of the fruit at harvest.

“Despite the differences in visitation, we found little variation between the production areas in the mean number of seeds or empty carpels per fruit – two key factors that can each influence fruit symmetry,” Dr Groom said.

Compared to wild insects, almost 12 times as many honey bees were observed visiting flowers.

Increased visitation by honey bees significantly correlated with the number of seeds per apple as well as fruit symmetry. However, there was no effect on the number of empty carpels per fruit – another factor in the development of uniform fruit.

By contrast, despite their relative rarity, visits by wild insects correlated with a reduction in the frequency of empty carpels but not with the number of seeds per fruit. It is therefore possible that in areas other than Stanthorpe, wild insects make up for the relatively lower numbers of honey bees per flower.

Dr Katja Hogendoorn, University of Adelaide, confirmed that the results reinforce the importance of sustainable production practices.

“In an industry facing increased competition for access to managed pollinators, these results suggest that supporting diverse pollinator communities through supportive landscape and sustainable production practices may help secure pollination services and consistency in fruit quality,” she said.

“This is particularly true when an incursion of the Varroa mite would diminish free pollination by feral honey bees and consequential demands drive up the costs of managed honey bee hives.”

Importance of flowering plants

Regardless of crops or region, researchers found what they all have in common are that they depend on the presence of flowering plants in the landscape.

“We found that the proximity and composition of native vegetation influences the abundance and diversity of crop pollinating species, with effects noticeable up to 200 metres into the crop,” Dr Hogendoorn said.

“In less forested areas, the densities of feral honey bees are not high enough to provide all the pollination required, because, in addition to nectar and pollen, their presence depends on the availability of nesting hollows and water.”

All pollinating species rely on the presence of floral resources, pollen and nectar. Different species are active at different times of the year – also when the crop is not in flower.

Dr Hogendoorn said to enhance the health and diversity of pollinators and ensure that pollination services remain reliable and resilient now and in the future, floral support should be available nearly year round, in close proximity to the crop.

“Most crop pollinating insects, including honey bees, are generalist feeders that have a broad diet, and require the presence of a variety of pollen and nectar sources,” she said.

“Our advice is to plant a wide range of local, easy to grow native species. Planting designs can focus on understorey species, hedgerows or whole area plantings. These plantings also convey a range of other benefits for farm productivity. You can find more information about this in the 2020 spring edition of the Australian Fruit Grower.

“In addition, nesting substrate for volunteer pollinators can be provided in various ways. This includes bundles of sticks with pithy stems for reed bees; open, compacted well drained soil for ground nesting furrow and nomia bees; and leaving old paddock trees in place as they provide nesting hollows for feral honey bees and, in NSW and Queensland, stingless bees.”

An interactive tool has been developed to run simulations on revegetating the area around your farm to support pollinators and how that affects your crop, as well as designing planting strategies focusing on South Australian growers.

Want to learn more? Head to the Pollin8 website.

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