The bees and the (gum) trees

The Western Cape has a superb indigenous pollinator — we must look after it. By Anna Mouton.

If insects disappeared, humanity could probably survive on cereals and other non-pollinated crops, but we would lose about a third of global food production. A 2017 Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services assessment estimated the annual global market value of pollinated crops as USD 235–577 billion. Crop reductions would also have knock-on effects throughout value chains.

Bee researcher Mike Allsopp of the Plant Health and Protection Division of the ARC and co-authors published a novel approach to calculating the value of honeybee pollination to the Western Cape deciduous-fruit industry. They estimated that replacing honeybee pollination with either hand pollination or pollen dusting would cost R530 million–R2.3 billion.

Although more than 20 000 species of insects, birds, and mammals pollinate plants worldwide, honeybees are the heavy lifters of commercial crop pollination. About 80 million hives of Western honeybees — Apis mellifera — provide managed pollination services globally. Of these, 14–18 million are in Africa, where Western honeybees are indigenous.

The top pollinator

Western honeybees dominate crop pollination for two reasons: they are social — colonies peak at 30 000–40 000 bees in summer — and generalists — they work on many different plant species. However, some environmentalists feel that other pollinators are being overlooked, especially in countries where Western honeybees are exotic.

Ecological entomologist Dr Ruan Veldtman of the South African National Biodiversity Institute participated in a global project to assess the contribution of wild insects to crop pollination. The project involved seven countries. The crops studied in South Africa were apples, sunflowers, and hybrid onion seeds.

The researchers quantified pollinator species richness and visits to crop flowers. They related these metrics to field size and crop yields.

Their results confirmed that honeybees are the only significant pollinators of the three crops studied. Insects such as carpenter bees and hoverflies accounted for single-digit percentages of total flower visits. “Overseas, they have bumblebees, which are social and good pollinators,” says Veldtman, “but we don’t have those in South Africa.”

Veldtman and colleagues also measured apple pollination on four Western Cape farms that relied entirely on natural pollinators. Their pollination was inferior to farms that brought in honeybee hives.

Veldtman argues that the international narrative framing honeybees in opposition to natural pollinators ignores a key characteristic of the South African situation. “We have a natural pollinator — it’s managed by beekeepers,” he says. “The bees in the beekeeper’s hive are genetically identical to the wild swarms.”

A special honeybee

The Western Cape is home to the Cape honeybee — Apis mellifera capensis —a subspecies of the Western honeybee. “Cape honeybees are adapted to Cape conditions,” says Veldtman. “They’re slightly darker, which may help with thermoregulation. They can work in about 2–3 °C lower temperatures than African honeybees.”

Honeybees in Africa have thus far proved relatively resilient to parasites and diseases that have devastated honeybees in other parts of the world. A 2009 publication by bee researcher Dr Vincent Dietemann and co-authors speculated that greater genetic diversity underlies the greater disease tolerance of honeybees in Africa.

African beekeepers tap into wild honeybees directly by trapping wild swarms and indirectly by uncontrolled mating of managed queens with wild drones. Dietemann and colleagues estimated there are more than 300 million wild honeybee colonies in Africa—or nearly 20 wild colonies for each managed hive.

In Europe, Western honeybees have been selectively bred for centuries. With wild honeybees almost gone, European honeybee populations have little chance of maintaining genetic diversity.

“We think the variety of plants our bees use also helps their resistance,” adds Veldtman. “That’s part of the ecosystem services our growers use, but of which they’re completely unaware.”

What forage is worth

Veldtman’s research interests include the interaction between ecosystem services and honeybee pollination. Ecosystem services are the benefits humans get from nature. Examples include the oxygen we breathe and the water we drink or use to irrigate deciduous-fruit orchards.

Pollination by wild insects is an ecosystem service, whereas managed honeybees are usually seen as an agricultural input. Veldtman reckons this is an oversimplification.

“The ecosystem service we use in the Western Cape isn’t honeybees flying in from remnant natural habitats,” he says. “Rather, it’s the processes that provide food for managed honeybees.”

A 2013 paper by the same team that calculated the cost to the deciduous-fruit industry of replacing honeybees examined the cost of feeding bees. The first author is agricultural economist Dr Willem de Lange of the Department of Agricultural Economics at Stellenbosch University.

In the Western Cape, crop pollination season is typically August to October for deciduous fruit and February to March for vegetables. Bees forage in fynbos from April until canola season starts in August. In December and January, they depend on eucalyptus.

If Western Cape beekeepers had to supply artificial feed during December and January, it would cost them about R140 million annually. Replacing the forage provided by eucalyptus with fynbos forage would require extensive fynbos restoration, raising the cost of forage provision to R390 million per year.

Veldtman was part of the team researching honeybee economics. “The forage that eucalyptus provides is worth about 20 times the value of the water it consumes,” he explains. “So, if you cut down the trees, you may save water, but you must consider the cost of replacing that forage.”

The case for eucalypts

Pollination services are fuelled by forage outside the pollination season. Managed bee colonies generally decline while pollinating orchards, especially when bees are expected to work under shade nets. Beekeepers depend on natural and semi-natural forage to rebuild colonies off-season and to support the wild bee population.

Finding suitable forage sites keeps beekeepers awake at night. They are not allowed to put hives in most protected areas, limiting their access to fynbos. They usually don’t own or control land with sufficient forage, so they must rely on landowners.

Besides providing forage, sites must be safe from fires, floods, predators, vandalism, theft, and chemicals — the list of threats to bees is long.

Veldtman is concerned that the demand for pollination services is outstripping the supply of hives and that reduced forage exacerbates the imbalance. He is collaborating with WWF South Africa and LivingLands on a new project to quantify the pollination demand in Grabouw and the Eastern Langkloof.

“If the pollination demand is higher than the number of hives the region can support, and they’re sourcing hives from other areas, then they’re being subsidised by the forage in other areas,” he elaborates. “Growers need bees to pollinate their trees — what are they doing to ensure bees are available in the future?”

One thing everyone can do right now is to stop the unnecessary removal of gum trees. Eucalyptus is not indigenous to South Africa, but of the more than 85 species that occur here, only six are classed as invasive. Unfortunately, one of those, the sugar gum — Eucalyptus cladocalyx — is a vital bee-forage plant.

Not all sugar gums need to be removed. WWF South Africa has compiled a guide to the regulations for landowners. The guide also outlines the importance of gums as bee forage.

“We have created a high demand for honeybees,” says Veldtman. “We need to find practical ways to ensure managed bees have forage while still looking after the natural fynbos and the wild swarms.