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

Hotel Hymenoptera: Why improper nest box design could be harming native bee populations

UntitledYou’ve probably seen them in a friend’s back garden, or a local park. Some are boxes or plastic containers stuffed with twigs and reeds. Others are formed by row after row of holes of various apertures,  bored into wooden blocks. These strange little garden features don’t appear to serve any immediate purpose, but if the sun is shining, and the weather is warm – hopefully you’ll be treated to the buzzing of one of the inhabitants: a bee.  These strange little structures are nest boxes, aka: bee hotels.

The public loves bees. And why shouldn’t we? Bees are unquestionably charismatic. The concept of a creature that meanders about from flower to flower, sipping nectar, and gathering pollen is the very definition of insect charisma. Meanwhile, the activity of bees provides us with some of the world’s greatest foods; Each almond, apple, pear, watermelon, and blueberry is made possible by the visitation of a pollinating insect (in most cases, a bee).

We love bees so much, that we go out of our way to make their populations flourish. We’re encouraged to use bee-friendly plants in our roundabouts, gardens, and parks. We protest and lobby against the use of pesticides toxic to bees, and as mentioned previously – we give bees homes.

Although bumblebees and honeybees might be the first kind of bees that come to mind, these new miniature developments we’ve been installing aren’t designed for them. They’re for solitary bees – which make up about 98% of global bee diversity. Rather than living in hives containing hundreds or thousands of individuals, working collectively for the common benefit of the colony – solitary bees use a totally different strategy.

Solitary bees live alone, many nesting underground. Many others live in the excavated pith of stems and twigs. Where the right cavity exists, the bee will create a brood ball – a densely packed sphere of pollen – where she will lay her eggs to develop into the next generation of solitary bees. By giving bees perfect nesting opportunities, we can give them the leg up by boosting populations.  Maybe.

While bee-nesting boxes are becoming increasingly more common in our gardens, it’s worth noting that it’s not just solitary bees that use the boxes. Ants and solitary wasps  have been known to colonise these structures.   The high density of nesting sites also mean that bees are more likely to experience attack by parasitoids. Furthermore in some locations, native bees are often outcompeted at nest sites by introduced bee species – likely causing knock-on effects where higher competition for floral resources, and increased disease transmission could further damage native bee populations.

To address this lack of knowledge, a study from the University of York set out to quantify whether the availability of nest boxes helped increase populations of native bees. The team set several hypotheses. The first was that because introduced bees have more flexible habitat requirements, bee hotels would be more likely to be colonised by non-native species. Secondly, because solitary wasps are less finicky requirements for nesting materials – they would be more common in nest boxes. Finally, as explained by the enemy release hypothesis – native bees will be more highly parasitized than introduced species. This would be further exacerbated by the unnaturally high density of bees found in nesting blocks.

By placing 200 ‘bee-hotels’ along a gradient of urban intensification in Toronto, Ontario – the team tracked which insects were using the nest cavities over three summers. In the autumn, the tubes within the next box were split, and each brood cell was placed into an individual container from where the adult insects emerged. All emerging insects were then identified to species. This was no small feat – considering that 27,000 individuals were collected during the three years of this experiment.

The team found no significant differences between abundance of native and non-native bees across all sites. However, native bee abundance was significantly lower than the aggregation of competing groups – comprising only 27.6% of all insects reared. The team found that native bees were three times more likely to be parasitized than introduced bee species. Providing these nest habitats didn’t increase the populations of any bees (native or non-native) across years, however the abundance of non-native wasps increased throughout the study (which could have been due to any number of factors).

The team concluded that bee-hotels as they stand today might not be the best intervention to increase native bee populations. They warn, at their worst, bee hotels could serve as population sinks for predators and parasites. As the unnaturally high density of nesting sites within a bee hotel is likely to cause higher rates of parasitism, perhaps creating less aggregated sites could be the answer to supporting native bee populations. On the flip side, parasitoids can often be more rare than their hosts, and bee-hotels could play an important role in conserving these at-risk populations.

While it’s wonderfully encouraging that the public are voicing their concern about the decline of native bees, and are actively searching for solutions –  it’s important that our steps to conserve their populations are helping rather than hindering. Many steps like planting nectar and pollen-rich plants, leaving woody browse in your garden, and reducing (or better yet abolishing) the use of pesticides in your are tried and true ways to keep the bees buzzing. While you’re at it, why not experiment a bit with different sorts of bee hotels?

As suggested by the researchers, more appropriately designed nesting sites could be the solution.  Try producing greater numbers of smaller nesting sites,  isolated holes in bits of wood, or leaving sandy bits of bare earth for mining bees to colonise. Try making openings available from 360-degrees, rather than in two dimensions to reduce the likelihood of a parasitoid attacking all the bees in your garden.

There are many ways to help native bees and other pollinating insects, but making them more susceptible to disease, parasitism, and predation by providing improperly designed trap-nests isn’t one of them. More research and increased responsibility by retailers of bee-hotels are required to reduce negative effects on bee populations, and to keep our gardens buzzing with life. But in the meantime, why not do a little bee-hotel architecture + experimentation yourself?

For a list of bee friendly garden plants, please check out these resources below.
North America: Xerces Society
Plants for UK and Mainland Europe – Royal Horticultural Society

References
MacIvor, J.S., Packer, L., 2015. “Bee hotels” as tools for native pollinator conservation: a premature verdict? PLoS One 10, e0122126. doi:10.1371/journal.pone.0122126

A tale of two introductions

toad_beetles

Native to Central and South America, cane toads have a permanent grumpy expression, and the chubby legs of a human toddler. They are large (a typical adult toad can measure up to 15-cm from snout to vent), and can be well over a kilogram in mass. In order to become big and strong, cane toads must consume an impressive number of calories. They achieve this by having a non-discriminatory diet, consuming: insects, other toads, plant matter, small mammals, and even birds.

The voracious appetite of the cane toad has made it a popular choice as a biological control agent. As toads hop through sugar plantations, they gobble up pest insects reducing the need for applying chemical insecticides. While early biological control programs augmented cane toad populations within their native range, scientists soon began to explore whether cane toads would be successful in new environments. After cane toad introductions to several Caribbean islands in the were successful in the 1930s,  a larger island, much further away began to show interest.

Across the South Pacific, Australia was struggling with a serious pest problem on sugar cane plantations. The cane beetle (Dermolepida albohirtum) – a small black and grey scarab native to Australia – was greatly reducing sugar yields. Having recently launched a successful biological control campaign to suppress the spread of prickly pear cactus, Australia gave the cane toads a shot – releasing thousands of young toads in the late 1930s.

Unfortunately, the toads did very little to control populations of cane beetles. The low levels of cover in sugar cane plantations reduced the foraging activity of cane toads. Additionally, adult beetles live near the top of plants and cane toads are ineffective climbers. Furthermore, the larvae of the cane beetles live deep in the soil feeding on sugar cane roots – far from the mouths of hungry toads. As the environment wasn’t right, and the food wasn’t accessible, the toads turned their bumpy backs on cane beetles. Instead they began consuming almost everything else, having devastating effects on Australian fauna.

The destructive impact that cane toads have had in Australia is not unique. The country has a long history of spectacularly invasive species which have been introduced either purposely or accidentally. Rabbits, camels, red foxes, feral goats, donkeys, and pigs are all thriving, and doing a number on the native flora and fauna. However, Australia is also the site of one of the most successful biological introductions to date: dung beetles.

In the 1960s, entomologist George Bornemissza realised that accumulating cattle dung was quickly blanketing pastures, where an estimated 2,000 km2  of land was lost to dung on an annual basis. While the immediate repercussion of  dung involves the limiting available grazing area, stagnant dung causes a myriad of other problems including: higher fluxes of greenhouse gases, increased rates of parasite transmission and provides ample habitat for pest flies to reproduce. The reason why this was such a problem in Australia was because a key group of insects were missing from the cow pats: dung beetles.

Australian dung beetles evolved to use the fibrous dry pellets of marsupials, and were unable to cope with the wet messy dung of bovines. In the late 1960s after careful planning and deliberation, the Australian government released 23 species of dung beetles from around the world at different points around Australia. These beetles had evolved to deal with dung of similar consistency, and went straight to work. Today, many species have successfully established and are thriving on the huge amounts of dung produced by the 29 million odd cattle in Austalia. While dung beetles free pasture from dung, their activity also improves soil fertility, removes habitat for the larvae of blood-sucking flies, and halts the spread of enteric parasites.

However, recent research from Australia demonstrates that these two introductions are interacting in an alarming way. Cane toads, which were imported to control a scarab beetle pest have instead switched their energy to controlling another type of scarab: dung beetles.  In a study published this week in the journal Ecosystems,  the profound impact our management choices have upon the surrounding ecosystems are clearly illustrated through the example of cane toads and dung beetles.

The study was conducted in the north of the Tarnami desert – which unsurprisingly is a hot and dry area. In order to raise cattle, you need to ensure that animals have access to plenty of water. As natural water sources aren’t terribly common, producers create water points through the use of boreholes and pumps. Water is driven from deep underground into two principal types of water sources : earthen dams where toads can easily access the water, or into large plastic or metal tanks which essentially removes toad access.

As cane toad tadoples need a reliable water source to complete development, and adult cane toads require also require intermittent access to moisture – the team hypothesised that there would be higher densities of cane toads near earthen dams in comparison to tanks. Because these toads are known to prey on all sorts of insects, they hypothesised that higher densities of toads would cause lower densities of dung beetles.  Finally, the team hypothesised that lower densities of dung beetles would mean lower rates of dung removal. By sampling at 13 different watering points (five dams and eight tanks), the team found crystal clear answers to their questions.

Population densities of cane toads were five times higher in areas surrounding earthen dams, than surrounding tanks. Abundance of dung beetles was 12 times higher near tanks in comparison to earthen dams, thought to be caused by high predation rates. Finally, the increased population of dung beetles at tanks meant 13% higher rates of dung removal in comparison to rates at earthen dams.

By making the switch from earthen dams to tanks, cattle ranchers can play a significant role in reducing the spread of a problematic invasive species, while protecting a group of beneficial introduced species. As tanks are less prone to evaporation and seepage, less water is extracted, meaning fuel is saved. This is a more economically and environmentally sustainable option for cattle ranchers. Hopefully with time, more operations will make the switch to slow down the toads, thus supporting dung beetles and the myriad  of ecosystem services they provide.

References
Baillie, C. 2008. Assessment of evaporation losses and evaporation mitigation technologies for on farm water storages across Australia. Cooperative Research Centre for Irrigation Futures, Irrigation Matters Series, (05/08).

Feit, B., Dempster, T., Gibb, H., & Letnic, M. 2015. Invasive Cane Toads’ Predatory Impact on Dung Beetles is Mediated by Reservoir Type at Artificial Water Points. Ecosystems, 1-13.

Lever, C. 2001. The cane toad: the history and ecology of a successful colonist. Westbury Academic & Scientific Publishing.

Nichols, E., Spector, S., Louzada, J., Larsen, T., Amezquita, S., Favila, M. E., & Network, T. S. R. (2008). Ecological functions and ecosystem services provided by Scarabaeinae dung beetles. Biological conservation, 141(6), 1461-1474.

Penttilä, A., Slade, E. M., Simojoki, A., Riutta, T., Minkkinen, K., & Roslin, T. (2013). Quantifying beetle-mediated effects on gas fluxes from dung Pats. PloS one, 8(8), e71454.

The curious case of the toxic slugs

If you’re in anyway tuned into the world of environmental news, you will have most certainly heard of neonicotinoids. Neonicotinoids (or neonics for short) are a class of chemicals which have become increasingly popular for controlling pest insects in agricultural systems. Neonics are highly toxic to insects, but usefully have low toxicity to birds and mammals.

While neonics have been widely adopted by farmers, they have less than a sterling reputation among many groups. Neonics work through a mode of action known as systemic delivery. This is achieved by coating the seed with the pesticide treatment. This active ingredient is then incorporated into the plant tissue, and is delivered directly to an insect feeding on any part of the plant. By applying neonics to seeds, riskier methods of pest control – like widespread spray programs – can be avoided during later stages of production. Due to their efficacy and relatively targeted delivery, neonics have become an important tool for suppressing insect pests.

The largest problem with the use of neonics is that they are applied  before their use is known to be required, a process known as ‘prophylactic application’. This process is analogous to taking aspirin to relieve a headache, you could foreseeably have later in the day. Over-reliance on a substance can eventually lead to reduced efficacy through pest resistance, and when little pest pressure is present – can contribute to the loss of beneficial invertebrates through non-target effects. When these two factors are considered together – potential damage caused by pest species is further exacerbated.

A new open access study published in the Journal of Applied Ecology has demonstrated a novel pathway through which neonics can impact the natural environment. This pathway involves a herbivore unaffected by the insecticide, which through feeding on treated plants become toxic prey for its predators.

No-till soybeans were the study system used within this paper. In the particular region studied, the dominant pest problems are caused by slugs. These slugs feed on the soybean seedlings, causing mortality and reducing yields. While the neonic treated plants are highly toxic to insect herbivores, slugs are unaffected by the presence of neonics. However, these slugs are kept in check by a diverse group of organisms including: ground beetles and farmland birds. We call these predators ‘natural enemies’. One of these natural enemies is Chlaenius tricolor – a wonderfully charismatic ground beetle. In the study region, these beetles are common within arable fields,  are highly mobile, and have a particular fondness for eating slugs.

In a series of laboratory experiments, the team confirmed that slugs were unaffected by consuming soy plants treated with thiamethoxam (a type of neonic commonly used to treat soybeans). However, when beetles were offered slugs which had fed on treated plants – more than 60% of individuals died or were seriously impaired.

The team then scaled this up to a field level, and found a similar pattern. In field plots grown from neonic treated seeds they found significantly higher densities of slugs, and significantly lower captures of natural enemies. Amazingly, the team even found five percent higher yields from non-treated seed (although pressure from insect pests was very low).

NEONIC_CROP

The rapid movement of a pesticide through this food-chain is an important reminder of how interconnected our food production systems are. It beautifully demonstrates sustainable agricultural production demands healthy ecosystems. While some would use the findings of this study as evidence for the condemnation of neonics and other insecticides within agricultural ecosystems, I wouldn’t agree. Insecticides remain an important tool within agricultural production. To me, the findings from these experiments serve to demonstrate just how cautious we must be with our application of pesticides.

The curious case of the toxic slugs brings to light just how complex, and sensitive our environment is. We need to think about the impacts of our actions on a multitude of scales. Whoever would have guessed that a predaceous beetle would be negatively impacted by chowing down on slugs made toxic by feeding on a neonic-treated soybean plant?

Reference:
Douglas, M. R., Rohr, J. R., Tooker, J. F. (2015), EDITOR’S CHOICE: Neonicotinoid insecticide travels through a soil food chain, disrupting biological control of non-target pests and decreasing soya bean yield. Journal of Applied Ecology, 52: 250–260. doi: 10.1111/1365-2664.12372