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Hoverflies and bumblebees are the most prolific urban pollinators in terms of the array of fruit and vegetable crops they visit in urban environments, according to a new study published today (Wednesday, 14 June) by researchers at the University of Sussex.  

The research paper, titled Crop-pollinator interactions in urban and peri-urban farms in the UK – which studied the behaviour of pollinators in cities - also found that strawberry plants in cities struggle to attract enough pollinators and may need help to be able to produce bigger and better crops.  

The study follows previous research from the University, which found that city allotments could be as productive as conventional farms. However, research into which insects visit fruit and vegetable crops and whether there are enough insects to successfully grow crops and sustain food production in cities has been little explored.  

Many of the fruits and vegetables that are grown in the UK require pollinators to produce fruit. Over two years, University of Sussex researchers observed the flowering crop plants in nine allotments in the Brighton and Hove area. They counted the number of pollinators that visited these crops, including bees, beetles, flies, hoverflies, butterflies and wasps. 

The research found that the highest rate of insect visits were to plants from the Rosaceae family, these include fruit bushes such as raspberries and blackberries and trees such as apples, pears and cherries. 

Bumblebees visited the largest range of crops, including tomatoes, broad beans, raspberries, blackberries and currants. Hoverflies were the most frequently observed insect visiting cherry and plum flowers, suggesting they may play an important role in the pollination of fruit trees in urban areas. Butterflies were recorded very infrequently, with only five crop visits observed.   

As well as observing insects visiting the crops, the researchers also ran a pollination experiment with runner beans and strawberries to test whether there are enough insects in urban allotments to sufficiently pollinate these crops to maximise yields.  

They assigned two closely sized plants to either a ‘supplemental pollination’ treatment, in which the researchers transferred pollen between flowers by hand with a paintbrush to supplement insect pollination, or ‘open pollination’ where they relied solely on the insects to pollinate. 

The research found that strawberry plants which were pollinated naturally by insects produced lower quality fruit than those receiving the supplemental-pollination treatment, suggesting there are opportunities for improving the quality of insect pollination some crops receive in urban areas. 

Dr Beth Nicholls, Research Fellow at the University of Sussex and co-author of the paper explains: 

“We know that allotments are visited by many different insects and this diversity helps to support the production of fruit and vegetables. 

“What our research shows is that urban crop pollination could be improved through the provision of food and nesting habitats for insects.  

“We observed that hoverflies are very effective pollinators of strawberries for example, so providing nesting habitat for hoverflies, such as hoverfly lagoons, would increase their abundance and ensure better pollination and therefore better and bigger strawberry harvests in future.” 

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