Case Study: Carabid beetles for natural-enemy pest control

Author: Kelly Jowett:

If there was an agent acting within your crops that could reduce eggs and first instar larvae of the cabbage root fly by up to 90%; reduce emerging wheat blossom midge by 81%; and reduce seed stock of crop weeds in the range of 65-90%, then I’m sure you’d want to keep it in there. Well, with a little effort you can have this voracious destroyer of pests working across your farm. Carabid beetles, sometimes known as ground beetles, eat ALL major crop pests, and weed seeds too, and are present in all farm habitats across the UK. This makes them ideal agents of natural enemy pest control.

Natural enemy pest control is a bit of a mouthful but is just what it describes: the eating of crop pests by the predators that would control them in a natural system. The problem for natural enemy pest control is that we are not dealing with a fully natural system. Since the post-war agricultural revolution, farmland has been subject to tremendous change. Over time this has caused substantial decline in the populations of carabid beetles and other natural enemies. Unfortunately, pest species are adapted to bounce back quicker - especially since large crop areas are ideally suited to support population booms. Whilst pesticide sprays are necessary in this system, they compound the problem - hitting the predators as well as the pests, added to associated resistance building.

The importance of biodiversity

Carabid beetles are incredibly variable. Of the 350 species in the UK, 30 of these are common in farmland. They range in size from 2mm to 3cm in length; some can fly long distances, some run up to 16cm per second; some breed in the autumn, and some breed in the spring. Each has their own habitat preferences, meaning that they are active at different times, tolerate different weather and farm management practices, and are better at eating different crop pests. Therefore, having a diverse range of carabid species will mean that you have the best chance of effective pest predation.

So what can we do to help boost carabid numbers and diversity?

Luckily carabid beetles are well studied and we already know a lot about what they need to thrive. We can break this down into areas to feed, areas to breed, and areas to shelter.

Areas to Feed

Of course we want them to feed in the crop or pasture area when pests are there- but pests are not there all the time (luckily for us!) to support the carabid beetles needs. So semi natural areas are essential to provide the invertebrate and plant resources for all year round food. Conservation headlands, grass/ flower margins, beetle banks and taking field corners out of management, can all provide these close to productive areas, so carabids can move quickly into the crop to eat the pests they prefer, when they appear.

Areas to Breed

Carabids lay their eggs in the soil, hatching into larvae- which take around 6 months to grow, before they pupate and emerge into adult beetles. The larvae are actually predatory on crop pests too, and eat more than adults as they need a lot of protein to grow. Some larvae also eat weed seeds, which is particularly useful as they live in the top soil levels in the crop area. To help larvae grow undisturbed in crop areas, minimum tillage systems may be useful.

Areas to Shelter

Carabids have two main periods when they need shelter: hibernation, and aestivation, which is a summer rest period when conditions are too hot and arid. At these times, the beetles take advantage of permanent habit with structure that creates a protective microclimate- such as hedges, ditches, banks, and at a small scale the tussocks created by some grasses.

Another important aspect is the shelter from machinery and chemical applications. These can cause direct mortality, or affect the carabids ability to feed and breed, so safe areas near to crops allow some beetles to thrive and repopulate when such management is necessary.

Linking up farm habitats

To preserve or enhance the diversity of carabids on your farm it is important to have a range of habitats, but also for them to be linked up. Firstly populations need those seasonal and foraging movements, but as conditions change, different species can immigrate into your farm from surrounding areas to boost your assemblage of species. Carabids move in the landscape in a variety of ways, flying species will use habitats as stepping stones, whilst running species may need ‘corridors’ of hedges and margins to encourage them to move around the farm.

Farm habitats for beetles. a) grass and flower margins, along with hedges provide food resources year round, and connect other habitats;
 b) beetle banks create stable resources in the centre of fields, to encourage beetle presence in crop areas;  (c) Peter Thompson
c) taking corners out of management encourages scrub and tussocky grasses- ideal for sheltering carabids.

Farm habitats for beetles: a) grass and flower margins, along with hedges provide food resources year round, and connect other habitats;  b) beetle banks create stable resources in the centre of fields, to encourage beetle presence in crop areas;  c) taking corners out of management encourages scrub and tussocky grasses- ideal for sheltering carabids.

But there is still work to be done

Although scientists have done a lot of research on carabids, there is still a lot we don’t know. My recent work has shown that different species are associated with different landscape features such as field boundary habitats, crops, soils, and management such as tillage regimes. If we can better understand which habitats are most beneficial for different beetles, it will become possible to tailor your farm habitats to get a good selection of predatory species that suit a farms particular pests.

Pitfall trapping to monitor farm habitats

Pitfall trapping is a quick and easy way to see what carabids you have on your farm, and if you do pitfall trapping periodically, you can track how the populations vary over time relative to your farm management interventions. For details see my factsheet:

 How to pitfall trap on your farm: Factsheet

Feed-back to scientists, especially me!

The main knowledge gap is how these habitats work in practice, over time. This is where we need to work with farmers closely, monitoring farm habitats, seeing what works, where, and why. But also, crucially, we need to know which interventions fit well into your farm business. Even if something works for beetles, if it’s going to be difficult for farmers to apply, it will not be widely applied!

Which leads me on to my plea: I need farmers to take my survey!

Watch my animation: Here.

Take a short introduction to ID quiz: Link to ID Quiz

Then take my beneficial beetles survey to tell me your opinions on carabids, management that may be useful for them, and monitoring. Link to survey

If you are motivated after reading this article to carry out pitfall trapping or set up monitoring on your farm, I would be happy to help with advice, and support with verification of carabid identification.

Email : Kelly.jowett@rothamsted.ac.uk or contact me on twitter: @kelly_jowett

Case Study: British dung beetles – here to help

Author: Ceri Watkins, Co-Founder of Dung beetle UK Mapping Project

Species: Dung beetles

Why is farmland important for these species?

There are approximately 60 species of dung beetle in the UK. They are not the ‘ball rollers’ seen in warmer countries and on TV, instead they live inside the dung pile (dwellers) or in the soil beneath it (tunnellers). Livestock grazing provides much of the dung required for the survival of these beetles, although other animals such deer and badgers also contribute. Some species are rather specialised and require exacting conditions. For example, Volinus sticticus prefers horse or sheep dung in the shade and Onthophagus joannae is a sun loving beetle that favours sheep dung on light soils. Others are less fussy and have few specific requirements.

It is possible to find dung beetles at work all year round. Several species are winter active, although the vast majority are found in the spring, summer and autumn. Given the right conditions, dung beetles can decimate a pile of horse poo or a cow pat in just a couple of days.

Volinus sticticus (c) Katherine Child  

Onthophagus joannae (c) Katherine Child

How do dung beetles benefit farms?

Dung beetles provide a wide range of ecosystem services that help to maintain healthy pastures and soils. These include the most obvious, the consumption of dung thereby removing it from the fields thus reducing pasture fouling, but also some that you may not have considered. As the beetles tunnel down through the soil, burying the dung for breeding purposes, essential nutrients are recycled within the soil profile. This improves grass growth and provides a direct benefit to grazing animals. The larger species such as the Minotaur beetle (Typhaeus typhoeus) can tunnel a metre or more, this action breaks up the ground and improves drainage, especially useful on clay soils.

In addition, dung beetles also reduce nuisance fly populations by transporting phoretic mites that eat fly eggs and help control intestinal parasites by reducing dung suitability for worm larvae. The beetles are also an important food source for many other farmland favourites such as bats and birds.

Onthophagus similis with phoretic mites (c) Ceri Watkins

Habitat management

Continuity of the dung supply and diversity of habitat are key factors in supporting a diverse range of dung beetle species on the farm. If possible, maintain some outdoor grazing year-round, even if only a few animals. Planting a group of trees and grazing within them will provide variety of forage and shelter for livestock and support the shade loving dung beetles too.

Broad spectrum livestock wormers such as avermectin are detrimental to beneficial dung invertebrates. These chemicals are excreted in the dung for many weeks after treatment and a range of lethal and sub-lethal effects occur depending on the concentration. Such effects include slowing beetle larvae development, reducing the size attained at adulthood and reduced breeding capacity.

Cutting down the use of chemicals on the farm with a sustainable worm control policy that includes monitoring with faecal egg counts will help. Treating animals only when necessary will save money and also slow the rate of anthelmintic resistance. As a natural alternative in a rotational system, consider using herbal leys. Sainfoin, birdsfoot trefoil and chicory all have anthelmintic properties. The latter has been shown to reduce worm burden in sheep by as much as 40%. In permanent grasslands, mixing up cattle and sheep grazing works by reducing the stocking density of the parasite host – cattle and sheep worms are different species.

Benefits

Supporting dung beetles on your farm not only helps keep pasture and livestock healthy, it also represents good economic sense. It has been estimated that dung beetles save the UK cattle industry £367 million per annum through the provision of ecosystem services (Beynon et al., 2015). So, it really does pay to look after these useful little creatures.

For further information and dung beetle identification resources, please visit the Dung beetle UK Mapping Project website or get in touch via email or twitter.