Gains and benefits

Field margin strips support natural pest control by:

1. acting as a permanent source habitat for natural enemies (such as carabid beetles, spiders) from where it can spread into the crop field, or

2. providing food or shelter when these are critically needed, e.g. pollen and nectar for species with ontogenetic diet shifts, such as green lacewings and predatory hoverflies (van Rijn & Wäckers 2016). If flowers are a limiting resource obviously depends on the landscape your farm is located in (Rusch et al., 2016; Van Rijn, 2017).

1. Field margin as permanent habitat

Strips of vegetation in the margins of crop fields can be the habitat of many (ground-active) predators including many different types of spiders, ground beetles (Carabidae) and rove beetles (Staphylinidae) (Mansion-Vaquie et al., 2017). These species can live in a field margin when it provides a minimum of resources needed during all stages of their life cycle (Kampichle et al. 2000). This includes prey both for young and mature stages, cover against frost in winter (Pfiffner & Luka, 2000; Galle et al., 2018), cover to hide from their (intraguild) predators (Davey et al., 2013), etc.

Crab spider catching a hoverfly (Foto: HOGENT)

The predators living in these strips can be triggered to move into the crop field

• to avoid competition when - after reproduction – local densities increase, and/or

• to benefit from high prey levels in the crop field e.g. due to pest outbreaks.

Field margin characteristics

To support generalistic, ground-dwelling predators the field margin should meet the following characteristics (Kampichler et al., 2000):

• permanent, mature, little disturbed,

• width 3 meter or more,

• have multiple perennial plant species, combining grasses and forbes (Mansion-Vaquie et al., 2017),

• sufficient cover in the winter (no mowing in autumn or winter) (Pywell et al., 2005)

• connected with other non-crop habitats.

To affect the pest control in the adjacent crop fields, species inhabiting these field margins should not be too different from those (potentially) inhabiting the crop fields, which is partly determined by the structure and family composition of the two habitats. Grassy field margins are therefore more effective for pest control by spiders and other ground-dwelling predators in cereal crops than other semi-natural habitats (Mansion-Vaquie et al., 2017).

This report (NL) provides more information on the role of field margins as habitat for beneficial insects.

2. Field margin as source of floral food

Due to a better understanding of the life cycles of beneficial insects, we now know that for many of them floral resources are essential for their existence. Many natural enemies of our pests are feeding on prey or hosts in their larval phase, while feeding on flowers when they are adults.

Flying natural enemies of pests, such as hoverflies, lacewings and parasitoid wasps require nectar and often also pollen as food source in the adult stage. The pollen is needed as a protein source for the development of eggs. The nectar is needed as an energy source for flying and surviving. They often even need the nectar on a regular basis, which means that it should be available in short range from the crop fields that you want to have protected against pests. Since weeds and other flowering plants have become rare in modern agricultural landscapes, field margin strips are now increasingly being promoted to offset the loss of these resources. Which plant species are suitable to feed these natural enemies is explained in ‘Selection of plant species’.

                                                                                                                                                     Larvae of predatory gall midge looking for aphids (foto: HOGENT)