How ‘natural enemies’ can be farmers’ friends

With evidence mounting that insect populations are declining, farmers are being encouraged to act now to save these vitally important species.

While some can be classified as pests, many – including earthworms, bumblebees and spiders – play a crucial role in breaking down organic matter, pollinating crops or providing a crucial first line of defence against more harmful species.

A new Farm Advisory Service fact sheet, Natural enemies, their lifestyles and how to promote them, highlights the importance of invertebrate species – particularly with the reduction in the availability and effectiveness of pesticides.

Written by Lorna Cole, an agricultural ecologist at Scotland’s Rural College (SRUC), and Paul Chapman, senior consultant at SAC Consulting, it says: “Managing farmland to support these beneficial invertebrates is an important component of Integrated Pest Management (IPM). Understanding the ecology of these natural enemies is our first step to protecting and increasing their populations.

“Determining where in a crop these natural enemies are active gives us an insight into the pests they will effectively control.

“There is even evidence that predators in different areas of the crop can work in synergy increasing the efficiency of biocontrol.”

While ladybirds, money spiders, hoverfly larvae and parasitic wasps are frequently active in the crop canopy controlling aphids, cereal leaf beetles and pollen beetles, ground predators such as rove beetles and wolf spiders will prey on leatherjackets and slugs at ground level. These insects can also work in synergy, with ground active predators consuming aphids which fall to the ground to escape ladybirds.

However, although it is important to support a diversity of ‘natural enemies’ in order to control the wide range of pests that damage crops, it can be difficult to achieve the perfect environment as different species require a variety of resources, and these vary throughout their lifecycle.

In order to overcome this dilemma, the authors recommend providing a diversity of farmland habitats, including floral-rich field margins, tussocky grassy field margins and hedgerows, and beetle banks, to provide forage and resources for the range of insects that protect crops.

They write: “The maintenance of a diversity of farmland habitats will not only favour natural enemies but also other economically important groups such as insect pollinators and wider biodiversity.”