Multitrophic ecosystem services of hoverflies in strawberry

Dylan Hodgkiss

Research output: ThesisDoctoral Thesis

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Agricultural advances in the last half-century have enabled the production of larger harvests. However, farmland is now at greater risk of pest outbreaks due to losses of genetic diversity within crops rendering crop plants more vulnerable to disease. Moreover, declines in biodiversity in the wider landscape mean that fewer predators of crop pests are present to control pest species. Equally worrying are recent declines in wild and managed insects that are necessary for the pollination of 84% of crop species in Europe. In commercial strawberry (Fragaria x ananassa), aphid damage is estimated to cost growers at least £2.5 million per year in the UK alone. Moreover, in the absence of pollinating insects, strawberry yields would fall by approximately £112.5 million per year.

In order to counteract these threats, I investigated the pollinator assemblages in commercial strawberry crops; the pollination effectiveness of aphidophagous hoverflies (Diptera, Syrphidae, Syrphinae); the effectiveness of planting wildflowers within strawberry fields to improve pollination and aphid pest control throughout the crop; and the gut contents of potential pest-controlling hoverflies within strawberry crops.

Retail and pick-your-own fruit farms have dynamic pollinator assemblages, including hoverflies. In cage studies, pollination by aphid-eating hoverflies doubled proportions of marketable strawberries when compared to insect-excluded controls. Coriander (Coriandrum sativum) planted within strawberry crops reduced aphid infestations and encouraged aphid predators to lay more eggs near aphid colonies. Furthermore, higher counts of pollinators were recorded in coriander plots, though no differences were found in fruit quality across all treatments. Finally, aphid DNA was recovered from the digestive tracts of hoverfly larvae. Prey DNA detection rates were greater near forget-me-not plots than coriander plots.

These findings suggest that hoverflies act as pollinators and pest-controllers in strawberry, and that by integrating coriander within strawberry crops their effects may be enhanced. Future work should focus on how to augment hoverfly populations in strawberry crops to further enhance their efficacy so that pesticide use can be further reduced.
Original languageEnglish
Awarding Institution
  • Royal Holloway, University of London
  • Brown, Mark J F, Supervisor
  • Fountain, Michelle T, Supervisor, External person
Thesis sponsors
Award date1 Mar 2020
Publication statusUnpublished - 2020


  • biocontrol
  • DNA barcoding
  • floral resources
  • fruit quality
  • gut contents analysis
  • intercropping
  • pollination
  • strawberry

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