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June 2020

Beneficial insect focus: Spiders – Ben Harrington, Edaphos

Beneficial insect focus: Spiders – Ben Harrington, Edaphos 591 340 Soilmentor

Edaphos offers agronomy services on all types of farms in all situations. Their philosophy is to improve soil and plant health, whilst harnessing the soils stored resources to their full potential to achieve a healthy, well balanced system.

Increasing biocontrol on farms by raising awareness of the beneficial insect community could lead to reduced pesticide use, costs and better support our own environment. In this blog we will be focusing on Spiders (which are arachnids and not an insect but certainly a most valued beneficial predator) through conservation biocontrol!

Before going into Spiders in detail, it is important to understand that to enable conservation biocontrol it is a direct focus on increasing the numbers and diversity of naturally occurring beneficial insects that are already within the area. To create a successful biocontrol through conservation alongside farming, predators and parasitoids need to thrive more so than in smaller production systems due to the fact that fields are subject to a whole host of management from us through mainly pesticide use, tillage, baling, mowing of margins and the management of field borders. Because a lot of fields are subject to the above, they don’t provide enough shelter, forage and overwintering habitat for many of our beneficial insects that would provide us with the wonderful benefits of pest control in crop and as a knock on effect, this also has an impact on other wildlife, pollinators and birds that are in a declining population.

The focus of conservation biocontrol is to focus on creating the necessary food and shelter and any other needs that has been proven to increasing numbers of beneficial insects. Once these are in place the biocontrol system will continue to develop and persist year on year as natures cycle of life and natural balance take place.

Back onto the Spiders! Hopefully over the winter and into the spring, many of you will have experienced spiders while walking crops, alongside margins or noticed a glint of an expanse of webs across the crop that is most noticeable at dawn and dusk which is a great sign and start to creating your biocontrol community.

Spiders are often the most abundant predator in agriculture although they play good and bad roles towards our purpose. Spiders are generalist predators which may feed indiscriminately on other insects and as you might expect for certain species their webs can cause chaos to any insects that fly.

Spider life cycles vary a lot between Arachne species, from species that have one generation per year and live for 2-3 years to those that are very short lived and have multiple generations per year. Spiders may lay eggs within silken nests in the soil, grass clumps, plant debris, under bark or inside hollow stalks of vegetation which these are the areas the adults also overwinter in as well.

For web-spinning species, vegetation as crops and weeds or a soil surface with adequate trash to create a diverse architecture provides a suitable habitat and hunting ground to spin webs. Leaving trash on a more cloddy surface with straw still standing helps retain web-spinning spiders in the autumn and the presence of the diverse architecture from the crop and arable weeds provides a suitable hunting ground in the spring and summer. Some web spinning spiders are capable of producing a long thread in which they can disperse themselves over long distances in a process called ballooning where they are carried in the wind. Web Spinning Spiders can offer us the first and one of the most effective controls against aphids in the autumn by covering whole fields in their threads from ballooning into and across the field. When they are present, you can easily see how and why they are so effective at aphid control and not many pests would get through their hunting grounds.

Wolf Spider (Wildlife Trusts, 2020)

For the hunting spiders such as Wolf Spiders and Jumping Spiders, they don’t rely on creating a hunting ground with their webs and will persist generally along field margins, hedgerows and plant foliage to hunt on the ground and will travel 50 metres into the field from these areas.

It is important to know that the more mobile species of Spider will only settle in locations with sufficient levels of prey and as such will show responses to prey densities. If you do not have the diversity or insect populations spiders will not be abundant.

To encourage the establishment of spiders you will want to integrate field margins as hedgerows, grass and pollinator strips into the field. Splitting fields with beetle banks or wildflower strips can help massively to improve coverage of these species into the field. Leaving crop residue and trash on the surface and leaving clods within the field will also give the spiders a diversity to their habitat and enable them to hunt effectively. Cover crops can also help to provide an ideal autumn habitat as a hunting ground and nesting site.

Flower rich margin

If you are interested in integrating Mid-Tier schemes for helping to promote Spiders and their necessary habitats and food sources the following would be useful to look into and integrate into the farm: Nectar Flower Mix (AB1 – £511/ha), Beetle Banks (AB3 – 573/ha), Flower Rich Margin and Plots (AB8 – £539/ha), Unharvested Cereal Headland (AB10 – £640/ha), Two Year Sown Legume Fallow (AB15 – £522), Autumn Sown Bumblebird Mix (AB16 – £550/ha), 4-6m Buffer Strips on cultivated land (SW1 – £353), In-field Grass Strips (SW3 – £557/ha), Winter Cover Crops (SW6 – £114/ha) and Woodland Edges on Arable Land (WD3 – £323/ha).

Spiders are highly vulnerable to pyrethroid insecticides and through good practice and management such as not spraying all fields with insecticide in one year and leaving some untreated, adhering to spray buffer zones and not spraying insecticides close to margins we should be able to minimise the risk to our populations of beneficials.

Soil Biodiversity #1: An Introduction

Soil Biodiversity #1: An Introduction 150 150 Soilmentor

Soil Biodiversity #1:
An Introduction

In this 6-part series we will delve into the role soil biodiversity and microbial activity plays in maintaining healthy soil. Read on to find out why focusing on soil biology is a must for all farmers!

Biodiverse soils are home to a rich tapestry of soil organisms – there are more microbes in a teaspoon of soil than there are people on earth! The soil community is made up of different trophic levels and functional groups; from microscopic bacteria and fungi to insects and our favourite wiggly friends, earthworms. These critters, large and small, make up the soil food web.

Soil organisms are an essential component in carbon and nutrient cycling, making nutrients available for plant uptake and creating stable forms of carbon stored in the soil. They create aggregated soil structure, allowing water and air, which are essential for plant growth, to percolate through the soil profile. They naturally buffer soil borne pests and diseases, purify water, clean up pollutants and boost resilience to climatic and environmental changes.

Each organism specialises in a particular function which is key to maintaining healthy soil. The whole biological community works together to provide these functions, it is tricky to isolate just a few organisms which are required, really you need a diverse mix. If soil biodiversity goes into decline, soil structure breaks down, leaving it vulnerable to erosion, as soil is unable to soak up moisture, leaving water to run off, taking soil and nutrients with it. Does this sound familiar – have you seen bare patches of soil and muddy water spilling into a nearby stream or river?

Relationships between soil biodiversity and food security pillars through soil processes and ecosystem functioning and services. Black arrows and black dashed arrows indicate, respectively, major and minor roles of functional groups on soil processes. Gray arrows indicate the relationships among supporting, regulating and provisioning ecosystem services.

Soil biodiversity is declining on many farms due to agricultural intensification and climate change. When we farm soils, we mine nutrients to grow crops, but are we putting these back in a way which improves soil health? Feeding soil with synthetic fertilisers is very disruptive to the soil community, rendering many of their functions redundant. If we begin to take the approach of nurturing our soil community, we will be richly rewarded with all the functions they can provide.

Stay tuned for the next installments in this series to hear more about functions soil biodiversity provide.

Sources

European Commission. (2010). The Factory of life: Why soil biodiversity is so important. Retrieved from: https://ec.europa.eu/environment/archives/soil/pdf/soil_biodiversity_brochure_en.pdf

Mujtar, V, E., Muñoz, N., Prack Mc Cormick, B., Pulleman, M., Tittonellad, P. (2019). Role and management of soil biodiversity for food security and nutrition; where do we stand? Retrieved from: https://www.sciencedirect.com/science/article/pii/S2211912418300300?via%3Dihub

Plaas, E., Meyer-Wolfarth, F., Banse, M., Bengtsson, J., Bergmann, H., et al. (2019). Towards valuation of biodiversity in agricultural soils: A case for earthworms. Retrieved from: https://www.sciencedirect.com/science/article/pii/S0921800918304610?via%3Dihub

van Leeuwen, J., Creamer, R., Cluzeau, D., Debeljak, M., Gatti, F., et al. (2019). Modeling of Soil Functions for Assessing Soil Quality: Soil Biodiversity and Habitat Provisioning. Frontiers in Environmental Science, Frontiers, 7, pp.113. Retrieved from: https://hal-agrocampus-ouest.archives-ouvertes.fr/hal-02280390/