Case study of crop pollination – Courgettes

Dr Jessica Knapp talks to us about the pollination of courgettes.

Plants in the Cucurbitaceae family provide a good example of crops benefiting from insect pollination. This diverse plant family includes fruit widely available today in our supermarkets such as melons, cucumbers, squashes and the courgette or ‘zucchini’. The flowers have hundreds of ovules which must be pollinated to produce the large fruits which contain hundreds of seeds. In their native range, cucurbits are visited by a variety of bee species, and the ‘squash bees’ are specialist on these crops and very effective pollinators.

When these crops are grown outside their native range, for example courgettes in the UK, then the local pollinator population need to do the job. To confirm whether pollination is being carried out successfully, we can compare the yields of flowers that have been hand pollinated or exposed to pollinators, with those that have not (flowers protected with mesh bags).

We then test whether there is a pollinator deficit i.e. whether the local population of pollinators are pollinating the crop for maximal yield. The difference between these two yields demonstrates whether there is a pollination deficit that could be reduced by increasing the number of pollinators in the field artificially (by introducing bees for instance).

For courgettes in the UK, our group found that the flowers could set fruit without any pollination at all, but insect pollinators increased courgette yield by 39%, and there was only a 3% pollination deficit, suggesting the local pollinator populations (mostly bumblebees) were doing a really good job!