Friday, July 1, 2022

Bee aware

Making better use of a range of insect pollinators can increase crop yields. According to Dr Brad Howlett, a pollination scientist from Plant & Food Research, a study on 20 crops showed a lift in yields when other pollinating insects were present alongside honey bees. This is primarily because different pollinating species distribute pollen to flowers differently, so a combination of pollinators will increase pollen distribution within crop flowers. Some crops are poorly pollinated by honey bees because they are unattractive to these bees or because the bees are ineffective at transferring pollen to stigmas. 

Other insect pollinators will also pollinate crops under climatic conditions not favoured by honey bees.

At the Foundation for Arable Research’s (FAR) Crop12 expo, Howlett outlined how arable farmers can make better use of insect pollination services to increase crop yields.

Honey bees, he says, are easy to manage and place in crops, but their future viability is uncertain because of pests and diseases such as the varroa mite.

Honey bees are also quite particular in their weather preferences, working best between 20 and 30deg C and in sunny, dry conditions, while many other insects will work in different climates; bumble bees, for example, prefer temperatures below 20 degrees and a higher relative humidity. Flies are also active in cooler conditions.

This country’s changeable weather means honey bees are inactive at certain times in certain conditions.

“Biodiversity creates more pollination in your crop.”

In some crops, pak choi for example, bigger insects are just as effective at pollinating the crop as honey bees.

A study done on hybrid carrot and onion seed crops found honey bees contributed less to pollination compared with flies; this is because the honey bees make far fewer movements between the parent lines. Thus crops dependent on unmanaged insects such as flies for pollination are vulnerable.

Flies, says Howlett, are unreliable pollinators because they vary greatly in abundance and distribution. He urged farmers to support research towards developing management strategies to increase reliability.

A lot of pollinators have to travel vast distances so Howlett says it is important to understand how they interact with landscape features.

On-farm factors also affect distribution and abundance of pollinators.

Using attractants to draw pollinators into the crop will allow a more even distribution of semi-managed pollinators.

Trials are under way to try to use artificial nests to build and manipulate populations of long-tongued bumble bees. These bumble bees are good for the pollination of white and red clover.

The short-tongued bumble bee is already used for the pollination of covered crops but understanding their nesting preferences could also lead to specially designed nest boxes in order to manage populations.

Native bees are just as good at pollinating as honey bees in crops such as kiwifruit, brassica and onion crops. They can form dense aggregations of several thousand bees in an area of less than 10m². A key goal is to understand what causes aggregations, because this could then be used to develop reliable techniques to establish large managed populations.

Other introduced bee species that are not being used include the leaf-cutting bee, which is used for lucerne.

Howlett says their potential role for being used over a wide range of crops has not yet been examined, but these bees don’t like wind.

Flies with management potential include the calliphorid and drone flies.

The callaphorid, particularly the European blue blowfly, occurs world-wide and is easy to rear. In New Zealand they are effective pollinators of brassica, hybrid carrot, and onion seed crops. They will forage in climatic conditions that don’t suit honey bees.

Howlett says further research is needed to determine the length of time adults remain foraging in crops and whether this can be manipulated to maximise retention in a required area.

Neighbouring land use, where flies could be a problem, needs to be taken into consideration.

Drone flies are an efficient pollinator of a range of crops including pak choi, carrot and onion. Drone fly larvae are common around dairy sheds where they live in water containing high nutrient levels.

Howlett says techniques for mass rearing need to be developed before this species can be managed. More information is needed also about fly movement. 

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