Briefing Sheet: Conserving Insects on Farmland

Insects are important to the ecosystem, pollinating plants and dispersing seeds, which are vital for agriculture and food production and, in turn, have an economic impact. They control populations of other insects while also providing a food source for reptiles, birds and fish.

Insect decline

As discussed in the What the Science Says piece on insect declines, many insect populations are in decline, and this is a serious concern. There needs to be long-term, in-depth monitoring to understand how insect populations are faring and what is causing the declines. However, we do know ways to help with this decline, even if we do not know all the information about a specific species.

Why are they declining?

There are many reasons for changes to insect populations. These include:

  • Loss and change in habitat, along with the plant species within those habitats – insect diversity is strongly linked to the diversity and number of plants.
  • Climate change: insects respond quicker to changes in temperature compared to other groups of species.
  • Pesticides: insecticides directly kill insects, whereas herbicides kill the weed plants on which some insect species depend on, affecting them indirectly.

How can we help?

Wildflower strip

Methods to support insect populations generally focus on the size and quality of habitat. This includes improving habitats by increasing the number of plant species and reducing dominance by any particular species. Other ways to improve quality are to create, conserve and reconnect habitats that have spilt. There are many management techniques which can benefit insects in different areas, including:

  • Creating new wildflower areas
  • Field margins without crops
  • Unharvested cereal headlands (Conservation headlands)
  • Allowing hedgerows to flower and increasing hedge bank plant diversity
  • Beetle banks
  • Increasing plant diversity in grassland
  • Establishing new broadleaved woodland (that are still managed) and ensuring existing woodland has a plant-rich understorey
  • Preserving diverse buffer strips around watercourses
  • Creating nesting areas of bare ground that can support some pollinators such as solitary bee species

Supporting insect populations is not just limited to farmland and large areas. In gardens, there are two simple measures: increase the number of native plant species and keep some areas untidy. Scruffy areas with some weeds are generally good for insects. Awareness and understanding of the methods required to support and improve insect populations are vital to their success, both in the farming community and the general public. Generating public interest and creating a plan for recovery are also important for insect numbers and diversity.

Farming and agri-environment schemes (AES)

The importance of insects on farmland
Pollinators are vital for crop yields.

Within an arable field, there can be between 1,500 to 3,000 different species of insects and spiders. Other habitats found in farmed landscapes also support diverse invertebrate communities, especially hedgerows, and although we don’t have an accurate estimate of the number of species, it is likely to be in the thousands, which include pests, beneficials, or those that are benign. Beneficial insects can be further classed as:

  • Pest predators that eat pests either as an adult or larvae
  • Pest parasites that live within the pest
  • Pollinators, vital for crop yield
  • Those which help break down organic matter

In an arable field up to 400 farmland predatory insect species, including beetles, spiders, mites, true bugs, flies and harvestmen may occur while surrounding non-crop habitats support many more. Consequently, there is a more diverse mix of insects and spiders within 60m of the field edge, but this decreases sharply as you move further into the field. Insects also provide a food source for farmland wildlife, such as birds, bats and reptiles.

The GWCT has conducted research on techniques to encourage beneficial insects, the natural enemies of pests, on farmland for many decades, some of this at the Allerton Project. More recently, research has been conducted with Kellogg’s Origins, investigating what is happening at the edge of crop fields and what natural resource methods would boost the number of beneficial insects, helping to control crop pests. Dr John Holland and Phil Jarvis have recently presented a seminar on ways to encourage beneficial insects and on the teams’ findings from the Kelloggs’s Origins project:

Habitat diversity
Following SAFE (shelter, alternative prey, flower-rich, environment) principles improves the quality of the farmed landscape.

An ideal landscape would have a mix of different crops, as well as non-cropped areas, creating a diverse habitat to support the wide range of beneficial insects, as shown in figure 1 and 2. There are four key criteria that need to be met to encourage beneficial insects:

  • Shelter (hedgerows, margins, areas protected from insecticides and intensive tillage)
  • Alternative prey (for when there are no pests, prey can be found on other crops, uncropped areas and weeds)
  • Flower-rich habitat (varied habitat and pollen and nectar plants to provide food)
  • Environment (limiting insecticide use, habitat management across the farm, habitat structure and diversity and creating microclimates)

For more information on the specific sowing conditions and plants needed for the following habitats, please read the AHDB Encyclopaedia of pests and natural enemies in field crops.

Hedgerows support a great diversity of beneficial insects throughout the year, but this depends on plant composition as the number of insect species associated with trees and shrubs varies greatly. For example, hawthorn supports 209 different insect species, whereas holly only supports 10. Hedges create micro-climates with a wide range of structures, providing shelter and sources of pollen and nectar. This is especially important for insects during the winter and no crop periods as hedge flowers can provide the food to improve fitness and increase their chance of survival.

To maintain insect diversity, the hedge should contain different structures and a variety of plant species, with new planting to replace gaps, containing species that support insects. Insect numbers fall after hedge cutting; therefore, hedges should not be cut yearly and not to a standard height as this doesn’t encourage new shoots. Trimming on a two to three-year rotation or by cutting incrementally at the end of the winter will help insects, hedges and flower production. Having a wide flower-rich margin between the hedgerow and arable field will act as a buffer zone, protecting the hedgerow from pesticide and fertiliser drift.

Grass margins and buffer zones are important, supporting a wide range of insects, especially through the winter by providing alternative foraging areas. Tussocky grasses are a particular favourite of beetles and spiders. Grassland is also likely to be beneficial if it is lightly managed and has a diverse mix of grass and herbaceous species. A range of grasses can create a variety of microclimates which will help support insects that are less able to control their body temperature, and are host plants for many butterfly and moth butterflies. Non-aggressive fine-leaved grasses are recommended, common bentgrass, crested dog’s-tail and sheep fescue.

Flower-rich habitats can provide multiple resources for beneficial insects such as foraging, breeding, and overwintering sites. In agri-environment schemes, the first and simplest option to be developed was the pollen and nectar mixes, now known as nectar flower mixes. They typically include clovers, vetches, bird’s-foot trefoil and sainfoin, which are preferred by long-tongued bumblebees and some butterflies. Flower-rich areas can also be created using a mix of fine grasses and perennial flowering plants, for example, knapweed, scabious, yarrow and bird’s-foot-trefoil.

The composition of these mixes is important and should be suitable for local conditions, especially soil type. To encourage a wider range of insects they can be diversified with flowers that have simple, open structures that allow for easy access to the nectar and pollen. For example, wild carrot, hogweed, cow parsley, angelica and yarrow are good options. Flowers with more complex structure encourage a more diverse range of bees, parasitic wasps, hoverflies, and flies with piercing mouthparts such as house flies, crane flies and bluebottles. Annuals are also useful for supporting beneficial insects, especially parasitic wasps and can be rotated with crops, for example, phacelia, buckwheat, alyssum, dill and coriander.

Parasitic insects are important for pest control on food plants but most need to move between crop and non-crop areas. They also need access to a source of nectar for nutrients, hence extra flowers would increase the levels of parasitic insects. Some species feed on weeds and their seeds while others consume fungi, which can reduce the need for weed and disease control.

Beetles and spiders like to overwinter in grasses because they provide stable environmental conditions even during the cold. They are good for pest control but this can only be achieved on large fields if beetles and spiders are spread across the field in the spring. In fields larger than 16ha, it is recommended to divide them with beetle banks. Beetle banks are raised strips, sown with a fine and tussocky grass mix, creating drier conditions favoured by insects. Wider strips can house more predators and are a better buffer from sprays.

Ideally, there should be no more than 150m between banks, encouraging both insects and other wildlife, such as birds. Beetle banks and other non-crop habitats reduce the distance over which these beneficial insects must migrate into fields. This will ensure a more even coverage, helping to control crop pests and potentially reducing the need for insecticides as well as increasing connectivity between these habitats.

Figure 1: The managed habitat created by crops and weeds influenced by the type and abundance of beneficial insects, from “Beneficials on farmland: identification and management guidelines”.
Figure 2: Best practice to encourage beneficial insects in the field, from “Beneficials on farmland: identification and management guidelines”.
Sowing methods

Many insects have life-stages in the soil, with large numbers of beneficial insects overwintering in the fields, including beetles, flies and spiders. These soil-based insects have important roles in recycling nutrients and controlling crop pests but turning the soil over with ploughing can disturb and kill them. Therefore, using non-inversion tillage practices will allow for beneficial insects to survive. The timing of seedbed preparation can also impact insect survival, along with the type of crop and associated pesticide use. Other measures such as under sowing cereal crops to establish a grass ley also helps soil living insects as the ground remains undisturbed. 

Crop diversity

Farming a varied mix of crops will help support a diversity of insects, lowering the risk of pest outbreaks. One of the biggest issues is crop type and the associated insecticides and herbicides used. Spring root crops come with more intensive soil cultivation, leading to fewer beneficial insects. How quickly insect numbers recover after this level of disruption depends on the surrounding area. In block cropping (the same crop in adjacent fields), recovery is slow and pest populations increase because there are fewer predators and parasites. Diversity in crops and having untreated fields nearby will help with recovery, lowering the pest risk. 

Insecticides and herbicides

Although some insects (pests) do feed on crops, very few cause economic damage because they are a food source for other insects. If the conditions change, favouring the pest or causing predator numbers to reduce, a pest outbreak develops. Farmers need to control agricultural pests, but insecticide kills a much broader range of insects including the beneficial ones. Furthermore, if the insecticide doesn’t remove all the pests but does remove the predators, this may lead to a pest outbreak. To reduce the impact of insecticides, they must be applied when only necessary, examining pest numbers and economic damage, then only applying to areas where there is damage, instead of to every field.

The most widely used insecticides, the pyrethroids, have a broad spectrum, leading to widespread impacts on beneficial insects. There is also a range of selective insecticides such as the carbamate insecticide Pirimicarb that targets aphids on a variety of crops, although even this product had some impact on non-target insects. Adopting Integrated Pest Management – the encouragement of natural pest enemies such as beneficial insects – can help allow farmers to reduce pesticide inputs but maintain yields.

Herbicides are also an issue, as they remove host plants. Weeds are very useful, providing an alternative food source by producing nectar, pollen and seeds and supporting herbivorous insects that act as alternative prey for pest natural enemies. They also create a diverse habitat and microclimates, supporting a wide range of insects, which, in turn, support farmland birds.

Arable plants (sometimes weed species) are also often visited by a range of wild bees and typically have simple flower structures that attract a broad range of insects. Allowing some of the less competitive weeds to survive by using selective herbicides, lower dosages and patch spraying more noxious weeds, can create a more beneficial environment. A range of insects, including beneficial insects, are also found in a range of AES options (see below) including unharvested cereal headlands (conservation headlands), wild bird seed mixes and with the option “cultivated areas for arable plants” that was specifically designed to encourage the rarer arable plants. This also attracts a broad suite of insects including many pest natural enemies. Weeds can also be left by not having pre or post-harvest herbicide treatments, this will provide more food resources for predatory insects. Keeping the field uncultivated throughout the autumn will lead to more seeds on the surface for insects and birds. Overall, minimising herbicide use and leaving areas scruffy is generally a good thing for insects.

Agri-environment scheme (AES)

The cost of enhancing habitats on UK farmland for insects can be recovered through some options in the national agri-environment scheme (AES). There are different levels available including entry, organic entry and higher level, along with the Rural Stewardship Scheme in Scotland and Tir Cynnal and Tir Gofal in Wales. Levels of pollination can be lower in larger fields because insects have to travel further into the crop, but larger fields are more economical to farm, so AES or other financial support may be needed to tip the balance in favour of smaller, more ecologically beneficial fields.

Agri-environment schemes need farmers that are willing to cooperate with each other. A study interviewing British farmers found there was a lack of communication between them. The authors suggested an external organisation to oversee joint operations and break down barriers, which 80% of the farmers interviewed approved of. The authors also suggest creating more collaborative agri-environment schemes, a more attractive option for farmers and likely to increase overall uptake to the schemes. This would involve farmers working with other farmers on an agri-environment scheme, instead of on their own, for example creating a network of hedges. Furthermore, they found farmers were more willing if they could enter part of their farm into the scheme so the ecological outcomes are achieved but the farmer can be more flexible. Since those proposals in 2012, farmers have started working together as Farmer Clusters and the approach has gained momentum, with over 150 clusters formed by 2020 across the UK. This is a farmer-led initiative in which they make the decisions about how to improve their clusters to achieve environmental gains. For more information about the approach, visit www.farmerclusters.com.

Public awareness of insects and their decline

Awareness of and interest in insect conservation is lower than for mammals and birds, and therefore there is a lack of public engagement. Most insect species are not an attractive cause that appeals to the public, especially when the media is full of images of other animals that are more impressive, cute and cuddly, such as tigers, pandas and elephants, which have benefited from marketing. All species are important, as is their conservation, but the awareness and coverage of some are limited because there is either no monetary gain or they just don’t come across as exciting. For example, bumblebees have a cute appeal which recently attracted more attention. Honeybees are vital for pollination, linked to food production, and butterflies are beautiful and eye-catching, therefore they are in the public eye. If people start to understand insects and care enough for them, and see them as a valuable commodity, there will be more drive to preserve them.

The key is to increase understanding of the different types of insects, their diversity and what they can offer. The use of “decline” when describing insect numbers might not be as effective to gain public support and action; instead, gaining knowledge about what is happening to them and communicating this, along with what it means to people, may be more successful.

The bigger picture: Roadmap to recovery

Figure 3: The road map to recovery for insects, eight no-regret solutions taken from Harvey et al, 2020.
Figure 3: The road map to recovery for insects, eight no-regret solutions taken from Harvey et al, 2020.

A roadmap to insect conservation and recovery was published in early 2020, arguing that although our knowledge about insect populations is far from complete, we know enough to act now on their conservation, and laying out eight no-regret solutions that could be adopted immediately to address this problem. These are proposed to be beneficial to society and biodiversity, even though their direct impacts on insects may not yet be fully known. The authors urge that, despite the knowledge gaps, action should not be delayed while we address them. They propose that enough is known to act now, whilst continuing with research in the areas that are still unclear and monitoring the impact of their proposals. These are illustrated in the diagram below:

Insect populations are often undervalued, but they provide the foundation for ecosystems and food webs the world over. As described in a report by the Zoological Society of London for the IUCN in 2012, “if invertebrates were to disappear tomorrow, humans would soon follow”

They also proposed multiple research aims to focus on to help understand the changes in insect numbers and diversity, including quantifying the trends in insect numbers over time to provide a new census; long-term studies comparing insect numbers and diversity between different habitats to understand what could cause differences; applying a standard monitoring system globally along with long-term monitoring sites that those are applied to and protecting, restoring and creating new insect habitats. They conclude that “a ‘learning-by-doing’ approach ensures that these conservation strategies are robust to newly emerging pressures and threats”.

In summary

In arable farmland, to maintain pest control but also support these beneficial insects, these practices are recommended:

  • Maintaining or creating flower-rich field margins, providing nectar and pollen for a wide variety of species.
  • Create beetle banks in fields greater than 16ha so wintering insects can control pests on cereal crops in the spring.
  • Plant new hedgerows in fields that contain beneficial plants. 
  • Use selective insecticides such as pirimicarb when needed and only on the area infested, using pest spray thresholds, and avoid prophylactic insecticide.
  • Avoid complete weed control as weeds provide food and habitat for insects important for pest control. 
  • Create conservation headlands around the edges of cereal crops. 
  • Use non-inversion soil tillage.
  • Have a diverse crop rotation and avoid block cropping. 

At home, in gardens, simple measures can be taken:

  • Increase the number of native plant species.
  • Leave some areas untidy; weeds and scruffy areas are generally good for insects. 

Public awareness needs to increase, helping the public understand all the benefits that insects offer and why it is so important to increase their numbers and diversity.

Please support our fight against misinformation

References

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