Dung beetles help reduce risk of E.coli transmission in lowbush blueberry systems

UntitledHumans and wildlife often have competing interests. In North America, this conflict is epitomised by the white-tailed deer (Odocoileus virginianus). Just take a moment to ask any gardener who lives in an area with a thriving population. Deer have a voracious appetite for tender plants. This is frustratingly paired with their ability to gracefully bound over fences with unparalleled ease. The white tailed deer can drive even the most pedantic of ‘deer-proofing’ gardeners insane.

But deer don’t limit themselves to causing nuisance in domestic gardens. They’re opportunistic generalist browsers, and agricultural fields are generally a perfect location for a nice feed. This can translate to significant yield losses for farmers. Voracious deer browsing can take precedence over many other pest problems, as there is little point in worrying about pests reducing yield quality, when your seedlings become deer fodder.

The damage deer exert on agricultural crops is not just limited to herbivory. The scat of deer can contain fecal pathogens, which can be spread to humans consuming contaminated product. E.coli-O157:H7 is a perfect example, where outbreaks in apple cider and strawberries are thought to have been caused by deer scat contamination.

Enter the dung beetle: Dung beetles are widely known to deliver a slew of ecosystem functions with benefit to sustainable agricultural production. Activity of dung beetles can reduce spread of parasites, improve the hydrological properties of soil, increase pasture herbage growth, and reduce pasture fouling (to name a few). Recently, a team from University of Maine, set out to test whether white tailed deer might act as a source of E.coli O157:H7 contamination in lowbush blueberry production systems and if so, whether a common species of dung beetle might play a role in suppressing the spread of this pathogenic bacterium.

The team conducted a series of experiments, described in detail in an open-access article published in PLoSThe first component was a field survey for different types of animal faeces; turning up scat from deer, black bear, snowshoe hare and wild turkey. The team collected more than 300 samples, and using laboratory methods determined that E.coli O157:H7 was present in lowbush blueberry fields (albeit in low presence 1.9% of samples).

The team then set out to test whether deer scat, would have the ability to vector E.coli to fruit. This was tested in a field experiment where deer scat spiked with a non-pathogenic strain of E.coli O157:H7 was dropped from 1-m height onto fresh berries. The fruit was harvested several hours later, and using laboratory techniques the team found that quick ‘glancing’ contact between the scat and berries was sufficient to spread E.coli.

There has been previous research conducted demonstrating that dung beetles might play a role in spreading diseases by inadvertently ‘piggybacking’ pathogens  between farms (Xu et al 2003). To test whether dung beetles might play in vectoring E.coli to fruit – the team turned to a common dung beetle known as the ‘scooped scarab’ Onthophagus hectate. The team placed live beetles in a terrarium with blueberry plants, and dung inoculated with the same non-pathenogenic strain of E.coli. Despite large amounts of contact of beetles and the dung –  O. hectate did not play a significant role in spreading E.coli to the blueberries.

Finally the team checked out whether this dung beetle was able to reduce the concentration of E.coli in the soil through their action of burying the dung. Because the fruit of lowbush blueberry hangs close to the ground, often resting on the soil – there is a strong likelihood of transmission from bacteria from the soil, or dung onto the fruit. Here, the team found that the activity of O. hectate significantly reduced the amount of colony forming units found in the soil – supporting the idea that dung beetles could play an active role in suppressing pathogen loads in wild blueberry systems. Dung beetles to the rescue yet again!

This work is another wonderful piece of evidence supporting the philosophy that conserving beneficial insects within landscapes can keep our agricultural ecosystems sustainable. Conserving beneficial insects in lowbush blueberry systems can help control pest populations and support pollination services. Other functions (like suppression of pathogenic bacteria) provided by beneficial invertebrates are often subtle, and can go largely unnoticed and unappreciated.

Next time you find yourself with a bowl of delicious lowbush blueberries – why not take a minute to thank a dung beetle. But for the sake of your health, it wouldn’t hurt to give them a quick run under the tap. Safety first.

References: 

Jones, M.S., Tadepalli, S., Bridges, D.F., Wu, V.C.H., Drummond, F., 2015. Suppression of Escherichia coli O157:H7 by Dung Beetles (Coleoptera: Scarabaeidae) Using the Lowbush Blueberry Agroecosystem as a Model System. PLoS One 10, e0120904. doi:10.1371/journal.pone.0120904

Nichols, E., Spector, S., Louzada, J., Larsen, T., Amezquita, S., Favila, M.E., 2008. Ecological functions and ecosystem services provided by Scarabaeinae dung beetles. Biol. Conserv. 141, 1461–1474. doi:10.1016/j.biocon.2008.04.011

Renkema, J.M., Manning, P., Cutler, G.C., 2013. Predation of lowbush blueberry insect pests by ground beetles (Coleoptera: Carabidae) in the laboratory. J. Pest Sci. (2004). 86, 525–532. doi:10.1007/s10340-013-0480-3

Xu, J., Liu, Q., Jing, H., Pang, B., Yang, J., Zhao, G., Li, H., 2003. Isolation of Escherichia coli O157:H7 from dung beetles Catharsius molossus. Microbiol. Immunol. 47, 45–49. doi:10.1111/j.1348-0421.2003.tb02784.x

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Beautiful British Beetles IV: The Minotaur

This is one of my absolutely most favourite beetles. I was shown my first one by my friend Richard, who found it in a very serendipitous moment on a night-time hunt. They’re slow, but faster than you think – a minotaur can slip into its tunnel faster than one would expect. I also came across this beautiful little beetles on Ramsey Island in Pembrokeshire, a gorgeous RSPB reserve known for its fabulous dung beetles (along with seabirds, choughs, pergrines, rare lichens, and a welcoming and knowledgable staff). Looking forward to searching out a couple of my own this weekend in Oxfordshire. minotaur_beetle

Chill out: climb a dung ball

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It is hard to make generalisations about insects. with unparalleled diversity – blanket statements are very rarely correct. Take for example dung beetles. Most people would recognise that dung beetles eat dung. This is mostly true, but some dung beetles prefer other diets: carrion, rotting fruit, mushrooms, and decaying vegetation are popular choices. One species of dung beetle has evolved carnivorous behaviour: feeding exclusively on millipedes.

A fascinating study from South Africa has illuminated a wonderful peculiarity about dung beetles. A common reproduction strategy for dung beetles in tropical ecosystems is telecopry. This is the process of forming dung into a ball, then rolling it away to safety. The main function of this behaviour is rolling dung to a safe place, where breeding can take place before the ball is buried safe within the soil. This also reduces the risk of a competitor stealing the valuable resource, the mate, or even another species parasitising the young.

In the case of the dung beetle Scarabaeus lamarcki, telecopry has taken on another role through being paired with a novel behavioural adaption. In a paper aptly named “Dung beetles use their ball as a mobile thermal refuge” the researchers demonstrate the vast utility of a dung ball. Scarabaeus lamarcki is known to climb the dung ball ball between short bursts of rolling, quickly preening, then continuing on its merry rolling way.

The first experiment compared beetles on hot soil, and soil cooled by shading. The experiment observed beetles as they rolled a dung ball from the centre of a 3 m diameter  circle. Beetles on cool soil exited the circle along an almost perfectly straight 1.5-m path. Beetles on hot soil stopped periodically to climb the ball and preen, taking three times longer on average to roll the dung ball out of the circle.

By looking at infrared images, the team found temperate of the beetles front legs climbed by roughly 10°C when running on hot ground. The beetles legs would cool quickly once they had climbed on top of the dung ball. However, that didn’t explain whether heat avoidance was the reason the beetles were climbing the dung ball. The researchers worked out a clever way of testing whether the beetles were climbing the dung to avoid heat stress: giving the dung beetles heat resistant booties.

Using dental silicon the researchers painted ‘boots’ on the dung beetles which prevented the transfer of heat from the ground to the beetles feet. Beetles with boots climbed dung balls 35% less often than their bootless counterparts. Demonstrating that the beetles were indeed using the dung ball as a mobile, thermal refuge.

These experiments are a powerful example of the wonderful ways beetles have achieved such widespread global diversity, and success. It also demonstrates that seemingly straight forward behaviours can mask latent, and rather sophisticated evolutionary adaptation. It would appear that there is truly more than one way to use a dung ball.

Reference:
Smolka, J., E. Baird, M. J. Byrne, B. el Jundi, E. J. Warrant, and M. Dacke. 2012. Dung beetles use their dung ball as a mobile thermal refuge. Current Biology : CB 22:R863–4.