Dung beetles vs Greenhouse Gases: Round Two

DB_Climate_change.pngProducing beef and milk comes with significant environmental costs. Cattle manure may harbour pathogens which have potential to contaminate waterways. Heavy trampling associated with intensive grazing can damage the structural integrity of the soil, making it difficult for plants to grow. Perhaps the largest impact cattle have on the environment is a little more abstract – the gaseous products of cows’ digestive systems.

Cattle are real wind-bags, belching out reams of greenhouse gases (predominately methane). These gases trap heat within the atmosphere, and contribute to global warming. As humans develop larger global appetites for beef and dairy products, the environmental costs of production will also increase. Luckily, have insects to help keep things in check.

When it comes to livestock production, dung beetles are a taxon that often come to the rescue. By burying dung deep into the soil, dung beetles can help reduce E.coli contamination on plants. The same tunnelling and burial action of beetles can also help repair damaged soil structure, improving hydrological properties, and reducing surface compaction. Dung beetles can even help regulate greenhouse gases from the livestock sector. While most greenhouse gases directly emitted from cattle come in the form of enteric fermentation (gaseous byproducts of digestive bacteria expelled via flatulence and burps), a study from 2013 demonstrated that dung itself acts as a source. However when dung beetles tunnel through, and feed on the dung – the team found reduced levels of methane emissions. Could dung beetles be part of the solution to greenhouse gas emissions from cattle? Possibly.

A recent study published in Scientific Reports set out to quantify the benefits dung beetles provide in reducing greenhouse gas emissions within the livestock sector at three scales: dung pat, pasture, and nationwide.

The team found that dung beetles played a significant role in reducing greenhouse gases when considered at the smallest scale: a dung pat. By capturing the gases fluxing from dung pats with or without beetles – the team found that dung beetles could reduce warming potential 7% relative to beetle free controls. When considering the impact of cattle at a pasture level, the effect was even larger – an impressive 12%. While this at first may seem counter-intuitive, the added bonus of dung beetles at a larger scale is due to cattle turning pasture from a sink to a source of greenhouse gases.

Finally the team looked at an impressively larger scale: across the whole beef and dairy industries in Finland. They used a technique known as life-cycle analysis. This is an approach that considers the impact of a product over its entire existence (birth-death). There are many inputs associated with conventional livestock operations that contribute to the impact of producing beef and dairy products. In Finland as well as many other northern-situated countries, cattle are unable to spend the entire year on pasture. This means that livestock hangout in barns during the off-season, often consuming grain and silage. Producing this feed comes with it’s own environmental footprint including : fertilisers, transport and soil tillage. Each of these sources adds up, which acts to continually dilute the benefits provided by dung beetles. The team found ultimately, due to a relatively intensive production system, and a short grazing season – benefits provided by dung beetles were a drop in the bucket – representing about 0.08% reduction in greenhouse gas warming potential in the wider context of Finnish beef and dairy industries.

The authors point out that while dung beetles play a relatively small role in reducing greenhouse gas emissions on a national scale, that their story is a small part of a bigger picture. Benefits provided by dung beetles is much greater when systems are characterised by: lower levels of agricultural inputs, longer periods of dung beetle activity, and greater time spent on pasture. These three factors are indicative of production methods practiced throughout much of the world – particularly in tropical environments. Competition for dung in the tropics tends to be stronger as well, where dung is quickly removed and buried. This action might act to further increase the beneficial roles that dung beetles play in reducing greenhouse gas emissions. As dung beetles are sensitive to environmental changes including: the use of veterinary medications, and deforestation – wider environmental disturbances could have the potential to spill over, increasing the footprint of livestock production.

NB: You can (and should) read this paper in its openly-accessible entirety over at Scientific Reports.

Beautiful British Beetles VI: The common cardinal beetle

CB122As summer starts kicking into high gear in the United Kingdom, these graceful beauties can be found on the wing. A shocking scarlet, cardinal beetles get their namesake due to their colourful resemblance to the vestments of  cardinals (no surprises there). For your strange insect fact of the day, a report from 2000 describes a male P. serraticornis feeding on cantharadin secrections from an oil beetle.

Cardinal beetles are generalist predators, chowing down on a wide variety of small invertebrates. They also occasionally take pollen. Their larvae live within decomposing wood, feeding on fungal hyphae and small invertebrates.

There are a couple species of beetles in the UK which are similar. Two rarer types of cardinal beetle can be found. The Black-headed Cardinal beetle (Pyrochroa coccinea), is slightly larger and is a deeper blood red. Finally, the Scarce Cardinal beetle (Schizotus pectinicornis) has a black head like P. coccinea but is only about half the length. It is rare, with an extremely local distribution.

References:

Nardi, G., Bologna, M.A., 2000. Cantharidin attraction in Pyrochroa (Coleoptera: Pyrochroidae). Entomol. News 111, 74–75.

The Wildlife Trusts., 2015. Red Headed Cardinal Beetle.  http://www.wildlifetrusts.org/species/red-headed-cardinal-beetle

Beautiful British Beetles III: The granulated carabid

This is one of my absolute favourite beetles. It is widespread in both the United Kingdom, and Canada. I’ve often stumbled across it on warm summer nights scurrying across the pavement in town, and sometimes finding it under stones in the back yard. They can give a bit of a nip if you’re not careful, and the males have these amazingly fat toes they use to grab females with for mating. The entire genus Carabus is full of beautiful beetles. They’re definitely worth checking out. Will be sure to cover another from this showy genus.

C_Gran2

Happy Taxonomy Day!

March 19th is Taxonomy Day, a 24-hour period dedicated to the science of defining where biological organisms belong, based on their common characteristics. If the mnemonic “Kings Play Chess On Fine Green Silk” is familiar, you’ve already had a lesson in taxonomy. This represents how we classify organisms from the most broad category (Kingdom), all the way  down to the finest (Species).

For my Taxonomy Day post, I chose to focus on two species I am very familiar with Aphodius fimetarius and Aphodius pedellus. These species of dung beetles superficially look almost identical, and nobody realised that they were completely different species until they were kayotyped. This is a process where the chromosomes of an organism are isolated, stained, and examined under a microscope. When several different representative beetles of this brilliant beetle were examined under the scope, their chromosomes were completely different. There weren’t any examples of individuals where chromosomes looked like a mixture of the two types, meaning there were no instances of hybridisation.

Scientists then realised that the species had different morphological characteristics as well. One species had a more densely punctured pronotum than the other. Even more striking differences were found when the aedeagus (male genitals) of the two different species were compared. As the characteristics of individual beetles vary greatly from one to the next, it can be easy to lump things into species when they look the same. Through collaborations between traditional taxonomy, and new molecular methods – we can learn more about the wonderful diversity that often remains hidden out of sight.

ped_fim

Reference
Miraldo, A., Krell, F.-T., Smalén, M., Angus, R. and Roslin, T. 2014. Making the cryptic visible – resolving the species complex of Aphodius fimetarius (Linnaeus) and Aphodius pedellus (de Geer) (Coleoptera: Aphodiidae) by three complementary methods. Systematic Entomology 39: 531–547.