Author Edith Villa-Galaviz shares her team’s latest study exploring key pollinator species identity and behaviour for strawberry crops that can provide vital insights for improving crop yield.

Fourteen years ago, a PhD student collected a large dataset on the visitation and pollen loads of the insects that visited three strawberry fields in the South West England. For various reasons, the student couldn’t publish their paper at the time and the data languished in a drawer – that is until 2022 when COVID-19 restrictions prevented us from going to the field…

Every cloud has a silver lining and this pause from fieldwork last year presented me the opportunity to return to earlier data and investigate what we can about strawberry crop pollination.

The problem

At the time when the data were collected, headlines about the decline of pollinators were not as common as they are now. Many things have changed and farmers now know the importance of insect pollinators for food production. As such, they often supplement wild pollination with commercial bees.

However, like other crops with open flowers, strawberries need many visits by different pollinator species to avoid malformed, lower-quality fruit. Supplementation of one or two bee species (usually honeybees and the bumblebee Bombus terrestris) is therefore insufficient and does not replace pollination by native pollinators which include hoverflies, and small and large wild bees.

On the other hand, managing the hundreds of species in the wild pollinator community is often overwhelming for farmers. We can help narrow this long list by identifying the key pollinators to make management more feasible.

Our study

Identifying the key pollinators with certainty can be quite laborious and time-consuming for ecologists and will often be unfeasible for busy farmers and other stakeholders. There are also further complications due to spatial variability in the set of pollinators present on a particular farm; the best pollinator on one farm may not be so, or even be present, on another. In this context, farmers need good proxies to identify key pollinators on their own farm and recommendations for habitat and other resources that might promote these species.

In our article, we compared two types of information to define the importance of pollinators for plants: pollen loads and flower visitation.

Pollen load is often considered a more accurate proxy for pollination service than visitation but the latter is easier to obtain and requires less specialised training. According to our results, these two methods overall give the same results. This is encouraging news for those interested in identifying key crop pollinators but without the resources to identify pollen loads! Bumblebees, hoverflies and honeybees were, in both cases, the most important pollinators for strawberries.

Within these broad categories, we found that the top pollinator species did vary between farms. To provide more general recommendations for farms that we did not study directly, we also looked for insect traits that were associated with high importance as strawberry pollinators.

We observed that key pollinators are abundant, relatively large and active for a long section of the summer. These traits are relatively easy to observe, allowing farmers to detect the key pollinators in their own fields even without species-level identification.

Notably, these key pollinators also feed on flower species beyond the crop even though strawberry is the most abundant flower resource in farms. This indicates that strawberry nectar do not provide sufficient nutrients to maintain insect pollinators and planting or maintaining a diversity of wildflowers near the field is likely to help promote wild pollinators.

Some of the key pollinator groups, including hoverflies, also benefit from nearby water sources as they have aquatic larvae while others, such as some bumblebees, need bare ground in which to nest.

Our article provides an overview of key pollinators of British strawberry plants, their traits, and their resource needs. It highlights that management needs to integrate different habitats and flower resources beyond field crops to ensure food production by providing what wild pollinator species need for their whole life cycles.

Read the full article: “What makes a good pollinator? Abundant and specialised insects with long flight periods transport the most strawberry pollen” in Issue 4:3 of Ecological Solutions and Evidence.