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2017 The aC ttle Dung Arthropod Community in Eastern South Dakota: Their oloniC zation, Impact on Degradation, and Response to Rangeland Management Jacob Pecenka South Dakota State University

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THE CATTLE DUNG ARTHROPOD COMMUNITY IN EASTERN SOUTH

DAKOTA: THEIR COLONIZATION, IMPACT ON DEGRADATION, AND

RESPONSE TO RANGELAND MANAGEMENT.

BY

JACOB PECENKA

A thesis submitted in partial fulfillment of the requirements for the

Master of Science

Major in Biological Sciences

South Dakota State University

2017

iii

ACKNOWLEDGEMENTS

This work could not have been completed without the help and support of numerous people throughout my studies at South Dakota State University. It is their time and assistance that allowed the studies, research, and analysis that I undertook to be possible. Committee members Dr. Jonathan Lundgren, Dr. Lora Perkins, and Dr.

Alexander Smart have been a source of guidance throughout the data collection and manuscript synthesis processes. I would especially like to thank Dr. Lundgren for his mentorship along this process. The education he has provided outside the classroom in how to become a successful entomologist and researcher have been invaluable during this process and will continue to be so throughout my professional career. The opportunities

Dr. Lundgren and the Ecdysis Foundation has provided me have allowed this vast undertaking to be possible and enabled creativity and passion to be a part of this research.

Many long days were spent in the pasture among the cows, digging through dung pats and collecting insects. Very often I came back to the lab dirty and tired only to begin the process of extracting, sorting and identifying the nearly 200,000 arthropod specimens collected throughout this study. I would like to thank Michael Bredeson, Claire LaCanne,

Dakotah Grosz, Kae Januschka, Nathan Koens, Marti La Vallie, Amy Lieferman, Abigail

Martens, Alexander Nikolas, Cassandra Pecenka, Greta Schen, and Kassidy Weathers for assistance in collecting and sorting field specimens. Insect identification assistance was greatly appreciated and was provided by Mark Longfellow, Chrissy Mogren, and Kelton

Welch. I also wish to thank the Ecdysis Foundation and NC-SARE for funding this research. iv

Finally, I want to acknowledge all the ranchers who participated in this study and allowed me to use their operations as sampling sites. I took what I learned from the ranchers that I worked with and applied it to my research. Getting to interact with them allowed me to see the importance of sharing information the essential line of communication needed when conducting agricultural research. I hope that the research conclusions included in this thesis will be a resource to ranchers in South Dakota and provide a greater knowledge of the little beetles doing the dirty work.

v

TABLE OF CONTENTS

ABSTRACT ...... vii CHAPTER ONE: INTRODUCTION OF CATTLE MANAGEMENT ON RANGELANDS AND THE DUNG ARTHROPOD COMMUNITY ...... 1 References Cited ...... 17 CHAPTER TWO: DEGRADATION OF CATTLE PATS IN EASTERN SOUTH DAKOTA AND IMPORTANCE OF DUNG BEETLES (SCARABAEIDAE) TO ADDITIONAL ARTHROPOD COLONIZATION ...... 32 Abstract ...... 32 Introduction ...... 33 Materials and Methods ...... 36 Results ...... 39 Discussion ...... 44 References Cited ...... 49 Tables ...... 55 Figures ...... 58 CHAPTER THREE: EFFECT OF CATTLE MANAGEMENT ON DUNG ARTHROPOD COMMUNITY STRUCTURE ...... 63 Abstract ...... 63 Introduction ...... 64 Materials and Methods ...... 67 Results ...... 70 Discussion ...... 74 References Cited ...... 79 Tables ...... 88 Figures ...... 97 CHAPTER FOUR: THE INFLUENCE OF CATTLE MANAGEMENT SYSTEMS ON PEST MAGGOT POPULATIONS IN SOUTH DAKOTA ...... 101 Abstract ...... 101 Introduction ...... 102 vi

Materials and Methods ...... 105 Results ...... 108 Discussion ...... 111 References Cited ...... 115 Tables ...... 123 Figures ...... 124

vii

ABSTRACT

THE CATTLE DUNG ARTHROPOD COMMUNITY IN EASTERN SOUTH

DAKOTA: THEIR COLONIZATION, IMPACT ON DEGRADATION, AND

RESPONSE TO RANGELAND MANAGEMENT.

JACOB PECENKA

2017

Cattle grazing operations are an important industry throughout the world and a vital component of the economy of the Northern Great Plains. Rangeland management is important to ensure that cattle grazing remains not only profitable but also environmentally sustainable. Conventionally managed rangeland systems that practice continuous grazing and repeated applications of chemicals such as avermectins pose a risk to the continuing productivity of rangelands. These practices have ecological consequences, primarily to the arthropod community that inhabits cattle dung pats. This diverse community works together to recycle dung pats and make the nutrients in dung accessible to the surrounding plant community, an essential role in the functionality of rangelands. The research within this thesis describes the influence of management systems on the dung arthropod community across eastern South Dakota. This community is represented by 172 morphospecies represented by 14 orders of arthropods that inhabit dung pats. We have gained an understanding of the community’s response to dung pat age and their contribution to the degradation of dung within pastures. A dung arthropod community with lower abundance, species richness and diversity will result in a dung pat takings 33-38 days longer to breakdown than pats accessed by an intact arthropod community. The management system strongly influenced the arthropod community and viii use of continuous grazing and avermectin parasiticides resulted in a disruption of arthropods living in dung. These conventional practices resulted in a lower number of beneficial predators, higher abundances of pest maggot species, and most notably; a decreased in abundance and diversity of dung beetles relative to management systems that used high density, rotational grazing and no avermectins. Dung beetles are keystone species within the dung fauna and their colonization of dung pats is essential for a complete community structure to occur within a pasture’s dung pats. Future research should continue to implement system level changes to a pasture over multiple grazing seasons and observe the changes in the dung arthropod community as well as economics of the management changes.

1

CHAPTER 1: INTRODUCTION OF CATTLE MANAGEMENT ON

RANGELANDS AND THE DUNG ARTHROPOD COMMUNITY

1.0 Rangelands in the US and Importance to South Dakota

Rangelands have changed substantially over time. Prior to European colonization, rangelands in North America encompassed the central and western portion of the continent, with the Great Plains bioregion alone extending across over 329 million ha

(Samson, Knopf et al. 2004). This large area provided a home for thousands of plant and animal species. The movement of Euro-Americans westwards greatly altered the Great

Plains. For example, the Homestead Act of 1862 provided land to settlers that incentivized the dispersion of a growing population (Reeves and Mitchell 2012).

Western settlers brought livestock to the region, including cattle ( Bos taurus ). Cattle and other livestock took advantage of the plentiful grazing space and replaced native large grazing species, such as the American bison ( Bison bison) , deer ( Odocoileus sp ) and elk

(Cervus sp) as the most abundant grazers on rangelands. More recently, Capper (2011) observed how the cattle system has changed within the last 30 years, with particular attention to how the industry affects the environment. Fewer animals (70%), less feed

(81%), and less land (67%) are required to produce the same amount of beef in 2007 compared to 1977. These more efficient systems are the product of a variety of technological and genetic advances that have been made in recent years. One advance that supports these systems is modern veterinary practices and medicines, but there are risks associated with these advances on the ecology of rangelands. 2

Today, rangelands include unirrigated land, grazed grasslands, and other areas of native vegetation. These categories make it difficult to identify the footprint that rangelands currently occupy nationally, but estimates vary from 40-50% of terrestrial surface globally (Yoshitake et al 2014). This land generates a substantial revenue. Cattle production in 2015 produced $59.9 billion in total sales, yielding 19 billion pounds of beef (NASS). More locally, 87.7% of land area in South Dakota is devoted to agricultural production, and 29.3% ($879 million) of state agricultural revenue in 2012 was generated by 14,306 ranches where 3.9 million head of cows and calves were produced (NASS). In addition to livestock production, other economic and ecological returns from rangelands include ecosystem services such as soil erosion control, increased water filtration, carbon sequestration, and habitat for a wide variety of plant and animal species (Goldstein,

Presnall et al. 2011, Steiner, Engle et al. 2014).

1.1 Rangeland Management Practices

Grazing management is defined as controlling when and where livestock graze on the landscape to attain a specific set of goals (Norton, Barnes et al. 2013). These goals can vary from generating profit to increasing the sustainability of the land by conserving the plants, animals, and soil natural resources. Therefore, it is very important that a rancher considers many aspects of their land when tailoring a grazing system to their individual operation (Anderson 1967). Here, we recognize two distinct approaches to managing herds: continuous and rotational grazing systems. Advantages between these two systems have long been debated (Sampson 1951, Heady 1961, Briske, Derner et al.

2011). 3

Resource requirements and their effects on the agroecosystem are two key ways that continuous and rotational grazing systems differ. In pre-European settlement of the

Great Plains, the large native herbivores were migratory grazers (Teague, Dowhower et al. 2011). Herds of these species moved across the landscape in response to vegetation and climate; these grazing patterns improved their grazing efficiency and the quality of their diet (Frank, McNaughton et al. 1998). Grazing management systems differ in the degree to which they mimic these historically grazing patterns. Continuous season-long grazing places all livestock on a single pasture for the entire season, with little rest or recovery of the pasture. A major benefit of continuous grazing systems is the ease of which a rancher can manage a large number of cattle, with minimal inputs of fencing, water sources, and transportation. As such, continuous grazing maximizes the short-term profitability of a pasture, but these benefits come at the cost of the long-term productivity of a system if grazing is not properly managed (Lodge 1970, Gillen, McCollum et al.

1998, Briske, Derner et al. 2008). Rotational grazing systems divide a pasture into multiple paddocks, and move the herd frequently (Briske, Sayre et al. 2011). After a relatively short grazing period the cattle are moved to the next paddock, giving the area a period of recovery and re-growth to recover lost biomass. Compared to traditional continuous grazing practices, rangelands managed with rotational grazing support more palatable forage (Earl and Jones 1996, Barnes, Norton et al. 2008), have higher water holding capacity (Teague, Dowhower et al. 2011), have more nutritious forage (Teague,

Provenza et al. 2013) and produce less bare or overgrazed ground (Jacobo, Rodriguez et al. 2006, Barnes, Norton et al. 2008). There is contention and debate about whether rotational grazing systems provide any advantages to ranchers. Reviews such as Briske et 4 al (2008) failed to show any significant advantage to the implementation of rotational grazing which illustrates the need for further work that calculates the relative costs and benefits of these two approaches to grazing. Movement patterns of the herd define these distinct approaches to grazing cattle, but within each of these systems there is a continuum of specific practices and characteristics like the number of pastures, pasture size, herd size, and duration of grazing events and herd re-entry (Briske, Derner et al.

2008, Roche, Cutts et al. 2015).

Even under excellent initial conditions, over-stocked rangelands where cattle are grazed continuously have a degraded natural resource base due to uneven forage consumption (Teague et al 2013). A large continuously grazed pasture is heavily visited in localized areas, while over half of the pasture is grazed at a monthly rate of less than 4 h per acre (Senft, Rittenhouse, and Woodnansee 1985). The heterogeneity of cattle foraging makes creating an efficient grazing regime challenging for ranchers (Norton,

Barnes et al. 2013). The loss of the desired palatable forage along with an increase of open ground surface can lead to weedy and invasive plant communities. Grass species such as smooth brome ( Bromus inermis ) and cheatgrass ( Bromus tectorum ) can more easily come to dominate continuously grazed pastures, thereby altering the native plant community through competition (Reeves and Mitchell 2012, Ellis-Felege, Dixon et al.

2013). Invasion by exotic species can increase soil erosion (Frost and Launchbaugh

2003), alter nutrient cycling (Evans, Rimer et al. 2001), affect the evenness and species diversity indices of native plant and animal communities (Frost and Launchbaugh 2003), and even reduce the grazing carrying capacity of rangelands (Vasquez, James et al. 2010,

Reeves and Mitchell 2012). Monoculture stands of invasive plants prevent a diverse 5 mixture of both cool and warm season grasses from growing, thereby limiting the variety of forage available throughout the entire grazing season. The direct and indirect economic losses from invasive plants that are encouraged by continuous grazing schemes are estimated at $27 billion annually and continues to grow (Stitt, Root et al. 2006,

Herrick, Lessard et al. 2010, Reeves and Mitchell 2012).

1.2 Cattle Dung and Nutrient Cycling

Dung composition and physical properties contribute to the nutrient cycling of pastures, as well as the chemical, physical, and biological properties of pasture soil

(Lovell and Jarvis 1996, Losey and Vaughan 2006, Aarons, O'Connor et al. 2009, Holter

2016). Pat degradation rates are affected by a combination of factors that vary according to weather (MacDiarmid and Watkin 1972), season (Dickinson, Underhay et al. 1981), and invertebrate community (Lee and Wall 2006). Dung physical properties influence its breakdown. Dung from cattle and other ruminants is composed of relatively small particles compared to that of nonruminants. The average size of cattle dung particles are about 0.31 mm which facilitates pat degradation (Fritz, Streich et al. 2012). The composition of fresh dung can be often divided into water (liquid portion), ash (mineral residues), and organic matter (OM or fiber; the undigested plant material that remains after passing through the animal), with each component varying with the diet of the grazer (Lee and Wall 2006, Holter 2016). The chemical profile of a pat also changes dramatically from the time it is deposited (Holter 1979, Aarons, O'Connor et al. 2009).

An important portion of the OM is the fecal nitrogen (N) content, typically present as

2.5% of the OM (Holter and Scholtz 2007). To a lesser degree, cattle dung also contains phosphorus (P) and potassium (K). These undigested nutrients within the dung pat will be 6 lost via volatization or soil leaching if the dung pat remains on the soil surface (Gillard

1967, Nichols et al 2008, Aarons et al 2009). Breaking up the pat and getting much of the material below the soil surface makes 80% more pat-derived N available to plants

(Petersen, Lucas et al. 1956, Gillard 1967).

The distribution of cattle dung pats creates a patchwork of higher nutrient density soils that affects the spatial structure of plant communities (Moir, Cameron et al. 2010).

The contributions of dung to soil nutrient status changes as the dung degrades. Even 112 d after a pat is deposited, the soil fertility, pH, electrical conductivity, and inorganic P within the top 10 cm of the soil profile under a pat was still higher than adjacent pat-free areas of the pasture (Aarons, O'Connor et al. 2009). The N of the dung is an important source of fertility for the adjacent plant community (MacDiarmid and Watkin 1972).

Dung-induced alterations to soil fertility increased the plant biomass and total productivity relative to elsewhere in the pasture (Aarons, O'Connor et al. 2009).

1.3 Problems associated with livestock dung.

When large aggregations of grazing cattle are on rangelands, slow dung degradation can adversely affect the environment (Fincher et al 1981, Anderson et al

1984). Proximately, the dung pat blocks light from reaching the soil surface and inhibits plant growth. Thus, large quantities of non-degraded pats can reduce the amount of forage available for livestock (Anderson, Merritt et al. 1984, Lee and Wall 2006, Losey and Vaughan 2006), and in degraded pastures the pats can persist for years (Merritt and

Anderson 1977, Anderson, Merritt et al. 1984). Greenhouse gas (GHG) emissions from rangeland make up 18% of all anthropogenic GHG emissions (Phetteplace et al 2001).

Two sources of N within these systems are nitrous oxide (N 2O) and methane (CH 4), 7 which come from the use of nitrogenous fertilizers, enteric fermentation from dung pats

(Lovell and Jarvis 1996, O'Mara 2011). Finally, dung is the habitat for a number of livestock pests, a topic which will be discussed at length later in the chapter.

2.0 Cattle dung arthropod community

Dung degradation is accelerated by a diverse group of invertebrates in search of habitat and food. As soon as the dung pat is deposited it becomes an “island” of resources for arthropods (Mohr 1943). Many of these species (e.g., tiny Collembola and mites) colonize from the soil near the pat. Others will colonize the dung pat from greater distances, following visual and olfactory cues to locate fresh dung. Even more species will respond to the influx of other invertebrates and use them as a prey (Tixier, Lumaret et al. 2015). These waves of colonizing arthropods form a diverse assemblage of species that inhabit cattle dung pats.

Members of this invertebrate community vary seasonally and as the dung ages, which allows for very fine niche partitioning and coexistence of a diverse assemblage of organisms in a discrete patch of resources (Mohr 1943, Valiela 1969, Wingo, Thomas et al. 1974, Lee and Wall 2006). Dung arthropod communities vary substantially across regions and even among grasslands within a region, even within the Northern Great

Plains (Fincher 1981). Communities fluctuate within a single location over the season

(Laurence 1954, McDaniel, Boddicker et al. 1971). More than 275 species of dung arthropods have been recorded in British cattle dung (Skidmore 1991) and up to 450 species of arthropods in North American cattle dung (Blume 1985). From the time of deposition to total degradation, a pat may exceed 1000 arthropod visitors (Laurence

1954). Few studies have been conducted in South Dakota from the last 50 years that 8 describe the dung arthropod community (McDaniel, Boddicker et al. 1971, Kessler and

Balsbaugh 1972). Investigations of dung arthropod communities provide a baseline to understand how management and environmental changes affect how these communities’ diversity and function change over time.

2.1 Dung beetles and other coprophages

Dung beetles (Coleoptera: Scarabaeidae) are a diverse group of insects, with

30,000 species worldwide and 1,500 found in North American (Ratcliffe 1970). Dung beetles are associated with dung of various mammalian species, but many are specialists on certain species’ dung. In North America, most dung beetle species are early colonists of dung pats (Holter 2016). Nearly all species in the group use dung (some exceptions consume rotten fruit or carrion), they provision this dung to their young differently

(Floate and Kadiri 2013). Endocoprid (dwellers) lay eggs within the pat or directly under it, where the offspring develops. Paracoprid (tunnelers) make brood balls of the dung, and deposit their eggs inside and bury these balls underneath the pat or adjacent to it. The final group are telocoprids (rollers), which make brood balls similarly to paracoprids, but they move the ball away from the pat and bury it beneath the soil surface.

In addition to dung beetles, other coleopterans perform a similar function of dung degradation. Hydrophilids (Coleoptera: Hydrophilidae) are one such family; it is not uncommon to collect 5-9 species and dozens of individuals within a single dung pat in temperate regions (Mohr 1943, Kessler and Balsbaugh 1972, Valiela 1974). The larger members of this family belong to the genus Sphaeridium , and these are some of the first beetles to colonize dung pats. They can arrive within 24 h of a dung pat’s deposition

(Hanski 1980). Another beetle family commonly found in dung pats in high numbers is 9 the Ptilidae. Little is known about these feather-winged beetles or their biology, but they likely consume decaying plant material and fungi growing within the dung pats

(Peitzmeier, Campbell et al. 1992). Coprophagous species are the invertebrates most associated with dung pat degradation, but they are not the only functional group of arthropods that inhabit cattle dung pats.

2.2 Predators and Parasitoids

Natural enemies of dung pat pests- predators and parasitoids- are an abundant functional group associated with dung. Predators colonize the pats after other species have colonized or reproduced on the pat (Valiela 1974, Wu and Sun 2010, Wu, Duffy et al. 2011). Many of these species are facultatively associated with dung, and can occur in other habitats as well. Parasitoid wasps (Hymenoptera: Pteromalidae, Ichneumonidae) that use filth flies (Diptera: Muscidae) as a host are often found in surveys of dung invertebrates (Mohr 1943, Valiela 1969, Cervenka and Moon 1991). Adult wasps locate pats of an appropriate age to find suitable hosts for their developing offspring (Kessler and Balsbaugh 1972). Filth fly parasitoids vary in their host specificity, with host ranges of 1-9 suitable fly species (Cervenka and Moon 1991).

Predators typically have broader diets than parasitoids, and completely consume multiple prey items over their lives; many predators are found in dung pats (Symondson et al. 2002). This general predation results in the consumption of both pest species and other coprophagous species found in the dung pat. Many species in the diverse family of rove beetles (Coleoptera: Staphylinidae) occur in dung. Staphylinid beetles are often one the most abundant predator groups, and they vary greatly in size from just a few millimeters more than 2 cm (McDaniel, Boddicker et al. 1971). Other predatory beetle 10 families include Histeridae and Carabidae (Kessler and Balsbaugh 1972, Valiela 1974).

Larvae of many of these beetles are also predaceous, but sometimes specialize on different prey species (Valiela 1969). Even in the later stages of pat degradation, predator species such as spiders, ants, and centipedes can be found eating the few remaining coprophagous arthropods remaining in the dried dung pat (Wu, Duffy et al. 2011).

Together, these predators and parasitoids combine to form a very effective community capable of suppressing undesirable pest species.

2.3 Pest dung insects

A variety of dipteran pests associated with dung can affect the profitability of cattle operations. The primary negative effect of flies on cattle is biting leading to blood loss, reduced weight gains from stress and irritation, and disease transmission (Campbell,

Berry et al. 1987, Mellor, Kitching et al. 1987, Floate 2002). The stable fly, Stomoxys calcitrans (L.), is considered one of the worst cattle pests in the world; it causes $2.31 billion (in 2017 dollars) in losses annually in the US (Catangui, Campbell et al. 1997,

Taylor, Moon et al. 2012). Another harmful bloodsucking ectoparasite, the horn fly,

Haematobia irritans (L.), is estimated to cause $1.92 billion (2017 dollars) in losses annually (Byford, Craig et al. 1999). Stomoxys calcitrans, H. irritans, and other fly species such as Musca domestica (L.) lay their eggs in dung pats where the larvae

(maggots) consume the dung, pupate and emerge as adult flies. These filth flies can have high reproductive potential, as each female is capable of laying thousands of eggs

(Pastor, Cickova et al. 2011).

2.4 Arthropod community’s role and function 11

Economic modeling suggests that dung removal services provided by dung beetles, a single component of the arthropod community, can save ranchers $442 million

(adjusted to 2017 dollars) annually (Fincher 1981, Losey and Vaughan 2006). Many estimates of value however rely on calculations done decades earlier and would benefit from a more current assessment. Studies on dung degradation have observed dung pats deposited in a landscape with an intact arthropod community can reduce 70% of a dung pats biomass over 1 m (Holter 1979, Strong 1992). Early colonization by relatively large scarab and hydrophilid beetles aerates the dung pat as they make tunnels; these tunnels then facilitate colonization by other species (Sanders and Dobson 1966). The tunneling through the dung pat by arthropods also can increase or decrease different gas fluxes leaving the pat (Penttila, Slade et al. 2013). Larger and more diverse invertebrate communities accelerate the benefits of dung degradation on soil quality (Fincher 1981,

Bang, Lee and Wall 2006, Losey and Vaughan 2006). The invertebrates associated with dung increase incorporation of organic matter (OM) in the soil, and improve the soil’s aeration and water-holding capacity (Bornemissza 1970, Macqueen and Beirne 1975).

Through these functions, invertebrates indirectly increase the pasture quality where dung was deposited.

Dung degradation by this group of invertebrates also removes pat-associated parasites such as nematodes, protozoans, and dipteran larvae (Byford, Craig et al. 1999,

Nichols, Spector et al. 2008) which all decrease the overall health and weight gain of cattle. Dung beetles and other coprophagous arthropods directly compete with cattle parasites and pests for the dung resource (Doube 1990, Ridsdill-Smith and Edwards

2011). Predators also take a toll on dung-associated pest populations. Dung pats with a 12 network of beetle-formed tunnels open pathways whereby predators can infiltrate the pats; these perforated pats produce fewer pest maggots (Valiela 1969). In addition to predators, female parasitoid wasps can reduce flies by up to 34% (Lysyk 1995, Floate,

Coghlin et al. 2000). Non-hymenopteran parasitoids, especially parasitoid rove beetles, can provide additional fly control (Cervenka and Moon 1991, Ferreira de Almeida and

Pires do Prado 1999, Balog, Marko et al. 2008). In fact, the rove beetle species Aleochara puberula (Kulg) had a higher parasitism rate of M. domestica (17%) than any of the wasp species tested (Ferreira de Almeida and Pires do Prado 1999). The adult of parasitoid rove beetles are predators of fly eggs and early stages of the larvae. By degrading dung quickly and fostering natural enemies, invertebrate diversity can be an important tool for reducing input costs associated with pest control (Geiger, van der Lubbe et al. 2010).

3.0 Avermectin use on cattle

Pest problems from internal and external parasites of cattle prompted the development of chemical products to combat these pests (Campbell, Fisher et al. 1983,

Meyer, Mullens et al. 1990). Synthetic pyrethroids, insect growth regulators, organophosphates and macrocyclic lactones (MLs) have been developed to combat pests of livestock. Avermectins, a group of ML, have been the most widely used group of anti- parasitic agents in the world since 1983, just two years after their introduction (Omura and Crump 2004). Avermectin was originally developed from Streptomyces avermitilis , an actinomycete bacterium isolated from soil. There are several different avermectin products that exist including the naturally occurring fermentation product abamectin

(MK936) and the most commonly used derivative, ivermectin (MK933) (Burg, Miller et al. 1978, Campbell, Fisher et al. 1983, Campbell 1985). Avermectins act as positive 13 allosteric regulators of glutamate-gated chloride channels which are normally inhibitory in nature, and the presence of avermectins force the channel to remain open

(Wolstenholme and Rogers 2005, Geary and Moreno 2012). Due to this agonistic action on chloride channels in nerve and muscle cells, plasma membrane permeability increases

(Albert, Lingle et al. 1986). This increased permeability leads to hyperpolarization of the membrane and decreases neuron transmission, often leading to paralysis and death of the pest arthropod (Omura and Crump 2004). These glutamate-gated chloride channels have only been found in Nematoda and Arthropoda (Geary and Moreno 2012). GABA-gated chloride channels are inhibited in a very similar way in the presence of ivermectin, although similar inhibitions of neuron transmission require much greater concentrations than the glutamate-gated chloride channels (Wolstenholme and Rogers 2005). The specificity and toxicity of avermectin products at low levels has resulted in sales of over

$1 billion each year in the US and application to over half of the nation’s cattle (Omura and Crump 2004, Losey and Vaughn 2006). All avermectins can be described as endectocidal drugs and all have a strong potency to a wide variety of nematode, insect and acarine pests and parasites (Campbell, Fisher et al. 1983). The potency of avermectins depend on formulation and on the method of administration (Sommer,

Steffansen et al. 1992). From subcutaneous injections, oral formulas in food, topical applications (“pour-ons”), and subcutaneously injected sustained-release bolus devices, there are numerous methods for administration that vary in the absorption of the products into the infected animal (Herd 1995). These different methods vary in their effectiveness in controlling the parasites as well as in the relative risks that these chemicals pose to non-target species (Strong and Brown 1987, Wall and Strong 1987, Strong 1992, 14

Ridsdill-Smith 1993, Floate 1998, Lumaret and Errouissi 2002, Floate 2007, Verdu,

Cortez et al. 2015). The remainder of this review will deal exclusively with avermectins, but other classes of chemicals can similarly affect the dung arthropod community

(Wardhaugh 2005).

3.1 Benefits of avermectins in cattle grazing management

Ivermectin, along with other avermectin products, successfully manage nematode and arthropod pests at very low doses. Antihelminthics typically require 5-88 mg/kg to manage nematode pests in cattle; ivermectin is effective at 0.05 mg/kg (Campbell, Fisher et al. 1983). One benefit of this pesticide is its low mammalian toxicity; avermectin only adversely affects cattle when administered at 40 times the label rate of 1 ml per 50 kg of cattle weight. This lack of toxicity is due to the presence of a blood-brain barrier in nearly all vertebrates that prevents the drugs from adversely affecting the host in the same way as the nematode or arthropod pest; this allows for avermectins to be used with minimal concern for livestock safety (Campbell, Fisher et al. 1983, Floate 2006).

The efficacy of the different avermectins has been well studied. Reviews have observed these different products on a variety of different insect orders (Strong and

Brown 1987, Floate 1998, Lumaret and Errouissi 2002, Desneux, Decourtye et al. 2007).

Avermectins had a strong negative effect on parasitic maggots that live on or in the host and dung-dwelling maggots are inconsistently controlled by the avermectin found in the dung depending on administration technique (Campbell et al 1983). The diversity of cattle pest species biologies (ecto/endo parasites) makes consistent suppression of pests with avermectins difficult. Different administration routes for avermectins will result in varying levels of pest suppression, depending on their life cycle or biology. The slow- 15 release bolus was very effective at killing anoplurans (blood sucking lice), and this technique suppressed egg production in Siphonaptera (Campbell, Fisher et al. 1983,

Gover and Strong 1996). In addition to livestock pest management, avermectins have played an important role in human disease management in the developing world, and this health program continues to grow (Rea, Zhang et al. 2010).

3.2 Hazards of avermectins in cattle grazing management

Avermectin’s potency to pest species can become an issue when the environmental persistence of the chemicals increases exposure of non-target arthropod species. The entire class of avermectins are metabolized less by the treated animal than other common pesticides and parasiticides, resulting in the presence of avermectin in the animal dung (Floate, Sherratt et al. 2005, Wardhaugh 2005). Ivermectin in particular has low retention in the host; with up to 80-90% of administered dose excreted in the dung.

This contamination persists for weeks following treatment (Campbell 1985). Ivermectin can be present in dung at biologically significant levels for 28-75 d or more; this is the same period that dung is most heavily colonized by beneficial arthropods (Sommer,

Steffansen et al. 1992). Avermectin formulation and application method contribute to the variability in dung contamination rates and durations. For example, the slow-release

(SR)-bolus capsules result in the longest dung contamination period, as they release the drug over a period of weeks. These products combine a long period of exposure with a very slow rate of active ingredient degradation. Ivermectin in dung has a half-life of 90-

240 d, with even longer potential during winter. This results in a long exposure period for all dung inhabiting fauna that could extend across multiple grazing seasons (Halley,

Nessel et al. 1989, Herd 1995). 16

Avermectins have a broad spectrum of activity within invertebrates, adversely affecting beneficial groups such as dung beetle larvae adults (Ridsdill-Smith 1993,

Rombke, Coors et al. 2010) and fly parasitoids (Floate 1998, Desneux, Decourtye et al.

2007). Still, there is limited understanding of how parasiticides affect local dung arthropod populations and their function. This limited understanding necessitates research that connects the use of avermectin products, such as ivermectin, and coprophagous arthropod populations. Perhaps most concerning is the numerous (albeit not always consistent) reports that avermectin is attractive to dung beetles (Strong, Wall et al. 1996,

Floate 1998, Dormont, Rapior et al. 2007, Floate 2007, Webb, Beaumont et al. 2010).

Dung beetles not given a lethal dose of avermectin often will experience reproductive deficiencies (Ridsdill-Smith 1993, Errouissi and Lumaret 2010) and reduced larval survival (Lumaret and Errouissi 2002), and sensory and locomotor impairments. The latter neurological effects can reduce pat-finding ability in adult beetles (Verdu, Cortez et al. 2015). This “attract and kill” outcome of avermectins suppress dung beetle numbers

(Wall and Strong 1987, Herd 1995).

4.0 Conclusions

Numerous management practices, from herd management to avermectin use, affect invertebrate diversity and abundance in dung pats. These management decisions combine to affect the function of invertebrate communities in dung degradation. Thus, valuable services such as pest reduction, nutrient cycling, and pollution control that are contributed biologically by invertebrates may be adversely affected by cattle management decisions that affect the profitability of a cattle operation. The purpose of this thesis is to 17 consider how these management decisions affect the diversity and function of dung invertebrates in South Dakota rangelands.

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of the Entomological Society of America 67 (3): 386-390.

Wu, X., Duffy, J. E., Reich, P. B., & Sun, S. (2011). "A brown-world cascade in the dung

decomposer food web of an alpine meadow: effects of predator interactions and

warming." Ecological Monographs 81 (2): 313-328.

Wu, X., & Sun, S. (2010). "The roles of beetles and flies in yak dung removal in an

alpine meadow of eastern Qinghai-Tibetan Plateau." Ecoscience 17 (2): 146-155.

Yoshitake, S., Soutome, H., & Koizumi, H. (2014). "Deposition and decomposition of

cattle dung and its impact on soil properties and plant growth in a cool-temperate

pasture." Ecol Res 29 (4): 673-684.

32

CHAPTER TWO: DEGRADATION OF CATTLE PATS IN EASTERN SOUTH

DAKOTA AND IMPORTANCE OF DUNG BEETLES (SCARABAEIDAE) TO

ADDITIONAL ARTHROPOD COLONIZATION

Abstract:

The failure of cattle dung pat breakdown on the soil surface in rangelands can create many problems for an operation such as suppression of plant growth, increased pasture fouling, and proliferation of pests. Here, we describe the arthropod community of dung in eastern South Dakota, and quantify their contributions to dung degradation using an exclusion cage design. Various arthropod community and degradation characteristics were measured in dung pats with and without arthropods excluded over time in early and late summer. A total of 86,969 specimens were collected across 109 morphospecies (13 orders) of arthropods, and enclosures effectively reduced arthropod abundance, species richness, and diversity. Dung pats without the enclosures degraded significantly faster than the pats with arthropods excluded, with the primary difference occurring within 2 d of pat deposition. Caged pats required 33-38 d longer to completely incorporate dung organic matter into the soil. Although dung beetles only represented 1.5-3% of total arthropod abundance, they were significantly correlated to more abundant and complex total arthropod communities. Provisioning for arthropod community function in dung contributes to sustainable and profitable cattle operations.

33

1.0 Introduction

When cattle excrete dung onto the soil surface the failure of the pats to break down can challenge the productivity of grazing on rangelands (Fincher 1981). When cattle consume forage, any nutrients not digested are returned to the system in the form of dung and urine (Haynes and Williams 1993, Wu and Sun 2010). The undigested plant material that makes up the dung pat is deposited on the soil surface, smothering plant growth in that area (MacLusky 1960, Holter 2016). Pasture fouling by accumulated dung that degrades slowly can represent a substantial problem to ranchers if left unmanaged.

When a dung pat is deposited on a pasture, all of the available forage underneath and within a 5 m radius of the pat is unused by grazing cattle until the pat is incorporated into the soil (Weeda 1967). Dung loses 22% (but up to 80%) of its nitrogen (N) to volatilization within 60 d of deposition (Weeda 1967, Nichols, Spector et al 2008). Other important nutrients such as phosphorus (P) and potassium (K) are present in dung pats in much smaller quantities and can be lost leaching and runoff when left on the soil surface

(Petersen, Lucas et al. 1956, Gillard 1967, Nichols, Spector et al. 2008). Volatilization and leaching reduces nutrient availability to the plant community, resulting in a decrease in the quantity and quality of forage for future cattle grazing (Bang, Lee et al. 2005,

Aarons, O'Connor et al. 2009).

A variety of factors affect how quickly dung is incorporated into the soil. Dung degradation rates vary widely in the published literature, ranging from 50-78 d (Holter

1979; (Lee and Wall 2006) and 88-111 d in late summer (Lee and Wall 2006), and up to

3 y in other systems (Anderson, Merritt et al. 1984, Strong 1992). This variability is due to factors including weather (Holter 1979), seasonality (Lee and Wall 2006), insecticide 34 use (Suarez, Lifschitz et al. 2003), and the quality of the dung itself (Cook, Dadour et al.

1996). Degradation of dung pats is facilitated by arthropods that accelerate the incorporation of the dung pat organic matter into the soil and improve soil’s aeration and water holding capacity (Macqueen and Beirne 1975). Dung often supports dozens or even hundreds of arthropod species (Valiela 1969, Merritt and Anderson 1977, Blume 1985).

Arthropods that colonize dung pats can be categorized into different functional guilds that each contribute to the eventual incorporation of the dung into the soil. One of the first studies considering the question of functionality of the dung community was

Mohr (1943), which prompted other studies that documented arthropod succession in a dung pat and their varying niches within the micro-habitat (Sanders and Dobson 1966,

Koskela and Hanski 1977, Cervenka and Moon 1991). These studies are accompanied by more recent explorations of the importance of dung beetles (Scarabaeidae) and the multiple ecosystem services that they provide (Nichols, Spector et al. 2008, Beynon,

Mann et al. 2012, Manning, Slade et al. 2016). One of these ecosystem services is dung beetles’ ability to increase the productivity of rangeland ecosystems (Bang, Lee et al.

2005, Penttila, Slade et al. 2013). Increased rangeland productivity is achieved by bioturbation and burial of dung that captures nutrients by forage plants within 12.7 cm of the dung pat (Bornemissza 1970, Macqueen and Beirne 1975, Yamada, Imura et al. 2007,

Aarons et al. 2009). A second important ecosystem service is the suppression of dung inhabiting pests to the grazing cattle (Fincher 1981). By removing nutritional resources and habitat, dung beetles reduce pest maggot abundance (Doube 1990, Nichols, Spector et al. 2008). Suppressing these pests is accelerated by the colonization of predator and parasitoid species to the dung pat. These ecosystem services provided by dung beetles (as 35 well as other members of the dung arthropod community) have an economic value to the ranching operation, but most of the numbers used to generate these values are at least 37 years old (Fincher 1981, Losey and Vaughan 2006, Beynon, Mann et al. 2012).

This study uses an arthropod exclusion/inclusion system to evaluate the role of dung arthropods on dung degradation over time in eastern South Dakota. Exclusion cages like those employed here help to isolate the contribution of the arthropod community to dung pat degradation (Lee and Wall 2006, Tixier, Lumaret et al. 2015). Here, we pair exclusion cages with a comprehensive description of invertebrate communities within the dung both early and late in the summer to understand how elements of this community affect degradation over the season. There are 9.12 million ha of rangeland in South

Dakota (USDA NASS), and this region represents an important transition zone between the mid and tall-grass prairie biomes. Dung-inhabiting Coleoptera from South Dakota were described nearly 50 years ago (McDaniel, Boddicker et al. 1971, Kessler and

Balsbaugh 1972), but these studies did not correlate these arthropods to dung pat degradation and the landscapes have changed dramatically over this period of time

(Wright and Wimberly 2012, Johnston 2014). Identifying the impact of the dung arthropod community on degradation will provide ranchers a greater understanding of the benefits to conserving this poorly understood community. We hypothesize that an arthropod exclusion system will limit the colonization in the dung pats and result in a slower rate of pat degradation.

36

2.0 Materials and Methods

2.1 Study site.

This study was conducted on a ranch in eastern South Dakota, U.S., at 44.758,

-96.538 in the summer of 2016. The study site was at an altitude of 559 m in an area with an average annual rainfall of 684 mm and an average summer temperature of 19.8°C. The

130 ha pasture was composed of mixed grasses; consisting mostly of Schizachyrium scoparium (little bluestem), Andropogon gerardii (big bluestem) and Spartina pectinate

(prairie cordgrass) with predominantly silty clay and silty clay loam soil types (USDA

Web Soil Survey). The grazing season prior to and during the experiment had a 130-steer herd made up of Angus, Belted Galloway, and Irish Black breeds, that was moved among small 0.41-1.21 ha paddocks approximately every 24 h. Cattle were excluded from the experimental site during the observation periods. No insecticide treatments had been used on the cattle for more than 10 y.

2.2 Dung degradation measurements .

Dung (< 2 h old; 90 kg collected twice) was collected from the pasture before

10:00. Fresh dung pats were homogenized and stored in bags at -25° C for 72 h to ensure all arthropods had been killed. Dung was thawed, and bags that appeared to have dried were reconstituted to their original consistency with distilled water. Aliquots of the dung

(1000 ± 10 g) were weighed and each “sentinel pat” was bagged and stored for 24 h before placing them in the field. Observation sites (n = 84) were placed in the pasture so sites were at least 5 m apart. At each site, a sentinel pat was placed on top of mesh with

2.5 cm square holes to allow for ease of pat removal. Each site was randomly assigned to one of three treatments. In the first treatment (inclusion; n = 36), dung pats were left 37 completely exposed with no covering. In the second treatment (exclusion; n = 36), the pats were surrounded by a PVC cylinder (25 cm diam., 25 cm tall), buried at least 12 cm into the ground to reduce ground colonization of the pat. The tops of these cylinders were covered in fine mesh screen (< 1 mm opening) and secured with plastic tie. The final control treatment (sham cage; n = 12) used the same cylinder design as the exclusion treatment, but with three 10 × 10 cm holes cut on the sides to allow arthropods to travel into the cylinder. A wire top was used to cover these sham cylinders that had 3 cm openings. This third treatment was added to test whether the exclusion cage had direct effects on dung degradation rates.

To determine degradation rates, pats from the three treatments were weighed over time. The entire experiment was repeated twice over the season, once beginning on

10-June and once on 28-July. Randomly selected pats (Inclusion [6 pats], Exclusion cage

[6], and Sham cage [2] on each time point) were removed 2, 4, 7, 14, 28, and 42 d after the sentinel pats were placed. Immediately at the time of removal the pat was collected in a plastic bag, sealed and taken to the laboratory. Each pat was weighed while still fresh and after drying to constant weight (over 7-10 d). A 10-gram sample of this dried pat was finely ground and baked at 500° C for 1 h; the remaining sample was then re-weighed to determine ash/mineral content of the sample. From this value the ash-free organic matter content (AFOM) of the pat was calculated.

2.3 Arthropod collection and dung pat analysis.

The pat was weighed and placed in a Berlese funnel system for 7 d to extract arthropods living in the dung pat. The arthropods were identified under microscope and then weighed to calculate arthropod biomass. To help characterize this diverse arthropod 38 community each specimen was identified to the lowest taxonomic level possible. Species were identified to at least the family level using Triplehorn and Johnson (2005); hydrophilid and scarabid beetles were identified to species using Lompe (2014) and

Ratcliffe and Paulsen (2008), respectively. For further characterization of the community, each morphospecies was assigned a functional guild depending on their feeding ecology.

The non-pest coprophagous community was divided into macro-coprophages (> 1 mm long; Scarabaeidae, Hydrophilidae), and micro-coprophages (< 1 mm long; Acarina,

Collembola, Ptiliidae).

2.4 Data analysis.

All statistics were conducted using Systat 13 (SYSTAT Software, Inc; Point

Richmond, CA). Two-way ANOVAs were used to investigate how dung pat age and exclusion cages affected dung pat and arthropod characteristics including; wet weight, dry weight, moisture content, organic matter content, arthropod biomass, arthropod abundance, species richness (number of morphospecies found), species diversity

(Shannon H), and abundance of family Scarabaeidae. To avoid possible pseudo replication and sampling bias, separate analyses were conducted on data collected early and late in the season. Linear regressions were generated to compare the number of dung beetles to dung pat organic matter, total arthropod biomass, arthropod abundance, species richness, species diversity and micro-coprophage abundance across (pooled across pat ages and early/late season observations).

39

3.0 Results

3.1 Dung arthropod community.

A total of 109 morphospecies (86,969 arthropod specimen) were collected from dung pats, representing 13 orders (Acarina, Araneae, Coleoptera, Collembola, Diptera,

Hemiptera, Hymenoptera, Isopoda, Julida, Lepidoptera, Lithobiomorpha,

Pseudoscorpiones, and Thysanoptera). There were 517.68 ± 30.98 (mean ± SEM) larval and adult specimens collected (228.02 ± 46.05 mg of arthropods), represented by 13.32 ±

0.49 morphospecies, per dung pat. Larval communities included only three orders;

Diptera (6 morphospecies), Coleoptera (17 morphospecies) and Lepidoptera (1 morphospecies). Orders with the most abundant specimens were Acarina (n = 35,534),

Coleoptera (adult n = 22,689; larvae n = 6,057), Collembola (n = 9,114), Diptera (adult n = 609; larvae n = 8870), Lepidoptera (adult n = 8; larvae n = 2,034), and Hymenoptera

(n = 1,141). Four families of Coleoptera were particularly well represented (they comprised 26% of all specimens collected): Staphylinidae (n = 8,140), Ptiliidae (n =

9,247), Hydrophilidae (n = 3,576), Scarabaeidae (n = 1,624) were represented by 14, 1,

12, and 13 morphospecies, respectively. Trophically, these specimens were categorized as coprophagous (29 morphospecies; 59,955 specimens), predators (38 morphospecies;

15,047 specimens), herbivores (18 morphospecies; 2,037 specimens;) or parasitoids (10 morphospecies; 539 specimens). The remaining specimens are regarded as coprophagous pests (14 morphospecies; 9,391 specimens), consisting of Diptera adults and larvae.

Arthropods were collected early and late in the summer. Arthropod abundances in the early season were 485.63 ± 42.18 (40,765 total) specimens from 12.91 ± 0.71 morphospecies per pat; 549.73 ± 45.36 (46,269 total) arthropods representing 40

13.73 ± 0.67 morphospecies per pat were collected later in the summer. Arthropod biomass per pat was 357.93 ± 40.98 mg in the early season and 152.72 ± 72.40 mg in the late season. Functional group populations changed across the two sampling periods.

Coprophage abundance significantly (F1, 166 = 5.08, P = 0.026) increased 25.30% (25,637 to 34,318), predator abundance significantly (F1, 166 = 9.11, P = 0.003) increased 40%

(5,661 to 9,386), parasitoid abundance significantly (F1, 166 = 24.36, P < 0.001) decreased by 78% (442 to 97), herbivore abundance significantly (F1, 166 = 7.89, P = 0.012) decreased by 53% (1,389 to 648), and pests significantly (F1, 166 = 12.25, P = 0.001) decreased by 76% (7571 to 1820) from early to late summer. Dung beetles represented

3% and 1.5% of total arthropod abundance in early and late season, respectively.

3.2 Sham cage effect.

The sham cages had similar arthropod communities and dung characteristics with the no cage treatment in 20 of the 22 statistical comparisons. Only early season arthropod abundance and late season dung pat wet weight were significantly different between treatments, but these trends were not consistent in both early and late seasons. The general lack of differences between the sham cage and no cage treatments indicates that the cage had little direct effect on arthropod communities and dung characteristics, and justifies our focus on cage/no cage comparisons for the remainder of this section.

3.3 Dung community between exclusion and over time.

Dung pats in the pasture had different arthropod communities when arthropods were excluded and as the dung pat aged. Exclusion and time had a significant effect on arthropod biomass in the early and late seasons (Figure 1). Arthropod biomass inside the exclusion cages was 10% of the biomass found in the inclusion pats early in the season 41 and exclusion pats had 13% of the biomass of the inclusion later in the summer. The biomasses of arthropods were significantly greater on younger pats (2, 4 and 7 d old) versus older pats (14, 28, 42 d old) both early and late in the season. Specifically, the biomasses declined by 72 and 83% between the 7 th and 14 th days in early and late season, respectively. After 14 d, arthropod biomass did not significantly change through 42 d.

Likewise, arthropod abundance was significantly affected by exclusion and time both early and late in the season (Figure 2). Similar to the biomass data, peak arthropod abundance was when dung pats were 7 d old in early season; arthropod abundance did not differ among the 2, 4, and 7 d old dung pats late in the season. In both early and late seasons, the 14, 28, and 42 d old dung pats all had significantly fewer arthropods compared to younger pats. Exclusion dung pats only averaged 52% and 57% of the arthropod specimens that were found in the inclusion dung pats in early and late seasons, respectively.

Arthropod species richness and diversity were also affected by exclusion cages.

The richness of arthropod species found in the dung pats was significantly affected by exclusion and time in the early season (exclusion: F 1, 60 = 102.86, P = 0.001; time:

F5, 60 = 9.18, P < 0.001; interaction: F 5, 60 = 6.71, P < 0.001) and in the late season

(exclusion: F 1, 60 = 66.49, P < 0.001; time: F5, 60 = 26.44, P < 0.001, interaction:

F5, 60 = 6.70, P < 0.001). The average number of species in the exclusion dung pats were

46% and 62% of the number in the inclusion pats for the early and late season, respectively. Exclusion and time had a significant effect on arthropod diversity (Shannon

H) in the early season (exclusion: F 1, 60 = 34.24, P < 0.001; time: F 5, 60 = 10.62, P < 0.001; interaction: F 5, 60 = 5.03, P = 0.001) but only time had a significant effect in the late 42

(exclusion: F 1, 60 = 0.402, P = 0.528; time: F 5, 60 = 50.19, P < 0.001; interaction:

F5, 60 = 5.53, P < 0.001) season. There were significantly more pest maggots

(F 2, 66 = 47.368, P < 0.001) in the exclusion than the inclusion pats. Dung beetle communities were significantly affected by the arthropod exclusion as well. In the early season, exclusion and time had a significant effect on dung beetle abundance (exclusion:

F1, 60 = 111.55, P < 0.001; time: F 5, 60 = 17.30, P < 0.001; interaction: F 5, 60 = 17.95,

P < 0.001). Likewise, in the late season exclusion and time had a significant effect on dung beetle abundance (exclusion: F 1, 60 = 105.01, P < 0.001; time: F 5, 60 = 23.85, P <

0.001; interaction: F 5, 60 = 23.85, P < 0.001).

3.4 Arthropod exclusion and time effects on dung degradation.

Arthropod exclusion and time had significant effects on dung pat wet weight in both the early and late season (Table 1). Dung in the exclusion treatment had an average of 26.10 and 21.93% lower wet weights than when arthropods were allowed access to the pats. Pats experienced a 28.3 ± 1.94% weight loss during the first 2 d. The weights continued to decrease over time until 20.30 ± 1.28% of the dung pat remained after 42 d of exposure (Table 1). Similarly, exclusion and time had significant effects on dung pat dry weight early and late in the season (Table 1). Moisture of dung pats was significantly correlated with arthropod abundance in early (F 1, 70 = 23.59, P < 0.001) and late

(F 1, 70 = 9.99, P = 0.002) seasons. After drying, the inclusion dung pats contained 25.45% and 25.10% less weight than the exclusion dung pats.

The AFOM percentage of the dried dung pats’ remaining weight were significantly affected by exclusion and time in the early and late seasons (Table 1).

Throughout the season the uncaged dung pats had significantly less AFOM than the 43 caged pats. Initially, 90.26% of dried dung pats were AFOM by weight, and by the 42nd day it decreased to 69-80% for inclusion pats and 80-86% for exclusion pats. Early season inclusion dung pats averaged 6.8% less AFOM than exclusion pats, and late season pats followed a similar trend with 3.14% less AFOM in the inclusion compared to the exclusion pats. AFOM content of dung in the early season was less than what was found in late season pats across both treatments (Table 1). Early and late season AFOM weight was also significantly affected by exclusion and time (Table 1), and the loss of

AFOM weight was different between treatments (Figure 3). Based on our calculated

AFOM rate of loss, early season dung pats with arthropods are estimated to completely degrade before 70.76 d. This duration increases to 103.85 d when arthropods are excluded from the pats. Late season dung pats achieve complete breakdown at a faster rate with estimates of 61.49 d and 99.82 d in inclusion and exclusion pats respectively.

3.5 Effect of dung beetles on arthropod community.

Although they represented 1.5-3% of the arthropod community recovered, dung beetle abundance, diversity, and richness were always positively correlated with arthropod community characteristics (Table 2). The abundance of dung beetles was significantly and positively correlated with total arthropod biomass, arthropod abundance, total species richness, and abundance of the micro-coprophage community in both the early and late seasons. Dung beetle species richness and diversity was correlated to an increase in abundance of the entire dung arthropod community in both early and late seasons (Table 2) (Figure 4).

44

4.0 Discussion

With few exceptions, the exclusion cages effectively reduced both the diversity and abundance of arthropods in cattle dung pats. There was significantly higher arthropod abundance and biomass found in the inclusion pats that were younger than 7 d old

(Figures 1 & 2). These significantly higher numbers of early colonization corroborate previous work that showed that the highest densities of invertebrates occur between 2 and

5 d post-deposition (Kessler and Balsbaugh 1972, Lee and Wall 2006). A majority of the arthropods found in the exclusion dung pats were small hydrophilid beetles, ptiliid beetles, mites, and Collembola, which collectively are described as “micro-coprophages”.

This group frequently colonized both caged and uncaged pats due to their small size and presence in the soil prior to cage placement. Another group found in both treatments was dipteran larvae; indeed, we found more maggots in the caged pats than the uncaged pats.

We observed that adult flies laid their eggs on the cage screen, and neonate larvae fell onto the pats. The effects of competition and predation on maggots in caged and uncaged pats are later explored (Chapter IV). Overall, there was a significant reduction in the abundance and diversity of most the dung arthropods in the cages. This allows an isolation of the function of arthropods in degradation of cattle dung.

Arthropod community complexity and abundance diminished as the pat aged.

Many of the early dung colonizers (flies and coprophagous beetles) consume small particles found in the liquid portion of freshly excreted pats (Holter and Scholtz 2007).

The offspring of these early dung pat colonizers add complexity to the community. Once sufficient numbers of these coprophages and their larvae have aggregated in the dung pat, a wave of predatory arthropods respond to this prey source (Koskela and Hanski 1977). 45

As the moisture evaporates from the dung, it becomes less attractive to many of the coprophages (Stevenson and Dindal 1987). Additionally, many coprophages migrate to more recently deposited pats (Mohr 1943, McDaniel et al 1971). Predators follow these prey species (Sowig, Himmelsbach et al. 1997, Slade, Roslin et al. 2016). This succession of colonization is supported by observations of arthropods during this study. Arthropod abundance decreased as the pats lost moisture, and by the time dung was14 d old, the arthropod community metrics and moisture content reached a constant low for the rest of the observation period. These observations resemble the succession of dung colonization seen in similar studies (Mohr 1943, Valiela 1969, Kessler and Balsbaugh 1972).

In addition to their changes over the age of the pat, dung arthropod communities also change over the season. In the early season, peak arthropod abundance was in 7 d old dung pats. Later in the season, peak abundance was in 2 to 4 d old pats, with a more gradual decrease in abundance as the pat aged (Figure 2). Several explanations may factor into why these patterns of seasonal dung colonization occurred. Temperature has an important effect on dung colonization (Errouissi, Haloti et al. 2004), with colder temperatures affecting colonization and degradation rates. In this study, early season had a colder temperature (16.67 °C daily average) than late season (21.11 °C daily average), and this may partially explain our experimental results. Higher temperatures later in the season would also dry the pat more quickly, and water content of the pat influences its attraction to dung arthropods (Finn and Giller 2000). This higher temperature causes the dung pat to dry at a quicker rate, making it less attractive and suitable for dung beetles and other large coprophagous arthropods. As the grazing season progresses, cool season grasses are replaced with warm season species (Ellis-Felege, Dixon et al. 2013). The 46 changes in palatability and digestibility of different plants to cattle can affect the composition of the dung and its attractiveness to arthropods (Holter 2016). Without further research, we cannot definitively say what drove these slightly different patterns of colonization over the season, but these considerations become important to ranchers wanting consistent dung degradation on their land.

Dung degraded more quickly when all arthropods were allowed access to the dung pat. Dung pat wet weight, dry weight, moisture percentage, and AFOM all decreased over time during the 42 d observation period (Table 1, Figure 3). The degradation characteristics also show that uncaged pats degraded faster than the caged ones. Ash-free organic matter (AFOM) has been proposed as the most accurate measure of dung pat degradation (Holter 1979). When arthropods are allowed to colonize dung pats, an AFOM was reduced substantially within the first 2 d (Figure 3). This quicker degradation may be explained by early colonization of the pat by relatively large arthropods. Dung beetles, especially members of the genus Sphaeridium , are some of the largest dung arthropods, and the amount of dung they consume and remove from the pat for oviposition is disproportionate compared to their abundance in the dung pats

(McDaniel et al 1971). After this first 2 d, the pats degraded at similar rates in both the caged and uncaged pats. When insects were allowed access to the pats, the pats had 32% of the original AFOM after 42 d; caged pats had 55% of the AFOM at the end of the observation period. Extrapolations of the data show that insects shorten the lives of pats

(i.e., complete AFOM removal) by an estimated 33.09 d in the early season, and by 38.33 d later in the season. These observations are comparable to dung degradation estimates made in similar studies (Lee and Wall 2006, Tixier, Lumaret et al. 2015). Often these 47 examples only exclude arthropods for short periods of time or focus on the collection of a single arthropod group, limiting the scale and scope of the observations made. Results show that early dung pat degradation sets the tone for the remainder of the dung pat’s time on the soil surface (i.e., the slopes of the regressions presented in Figure 3). This suggests that even a short period of exclusion could have implications for the duration of the pat’s life. Disruptions to early arthropod colonization can have long-term implications to the efficient recycling of dung pats.

These results provide further evidence that dung beetles contribute multiple ecosystem functions to rangelands by the dung arthropod community (Nichols, Spector et al. 2008, Beynon, Mann et al. 2012, Manning, Slade et al. 2016). Arthropod communities are major contributors to dung degradation, and dung beetle abundance and diversity influence many of the characteristics of this community (abundance, richness, and diversity) (Table 2, Figure 4). Dung beetles were significant drivers of the overall arthropod community even though they represented only 1.5-3% of the specimens collected in the study. Dung beetles colonize fresh dung pats and feed on the liquid portion of the dung; they leave when water becomes limited (Holter and Scholtz 2007).

Dung beetles may also deposit eggs in or underneath the dung pat, where their larvae will develop and consume the dried fibrous portion of the dung pat that remains (Laurence

1954). Dung beetles can also alter the dung pat and the arthropods that will colonize it.

Through their tunneling and bioturbation of the dung pat, they allow air to reach the center of the pat and cause it to degrade faster by converting it into forms accessible to plant roots and microbes (Bornemissza 1970, Stevenson and Dindal 1987, Bang, Lee et al. 2005). Dung beetles’ robust bodies also provide a “highway system” that other 48 arthropods such as predatory beetles or spiders can use to search for prey such as pest maggots. These tunnels also open up the pat’s interior to the micro-coprophage community that lack the ability to burrow through the pat; further increasing their effect on pat degradation. Their impact can be seen in the large amount of OM lost in the first days of arthropod colonization. This shows the multiple sizes or oviposition methods of dung beetles allow for a wider range of dung arthropods to colonize dung pats and contribute to degradation and a loss of organic matter in dung pats, resulting in greater available forage for future cattle grazing.

For ranchers in eastern South Dakota, the implications from this study can influence future grazing decisions. If they conserve dung arthropods, especially dung beetles, with management choices (e.g., limiting insecticide use) they can accelerate the breakdown of dung pats in their pasture. Dung beetles facilitate the use of dung pats by many other species of arthropods that can improve the rate of degradation by over a months’ time. With the relatively short grazing period in the region, rapid elimination of dung pats from the soil surface increases the available forage for grazing. This service contributes to the profitability of ranches through increased cattle weight resulting from increased grazing efficiency.

5.0 Acknowledgements

Authors thank Mike Bredeson, Claire LaCanne, Amy Lieferman, Alexander Nikolas,

Cassandra Pecenka, and Kassidy Weathers for their assistance in construction, deploying, and field removal of dung pat cages. Special thanks as well to Mark Longfellow in assisting with insect identification, and K Creek Ranch for use of their pasture. Ecdysis 49

Foundation and NCR-SARE, via student research grant GNC15-207, funded this research.

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55

7.0 Tables

Table 1. The effects of age on degradation of physical and chemical characteristics

of dung pats with arthropod community exclusion/inclusion. Capital letters

represent differences over time and lower case letters represent differences

between treatments (α = 0.05).

Days Wet weight of pat (g) Dry weight of pat (g)

Exclusion Inclusion Exclusion Inclusion Early 2 772.78 ± 24.34 Aa 585.11 ± 30.12 Ab 193.05 ± 4.18 Aa 147.38 ± 12.10 Ab Season 4 697.25 ± 15.58 Ba 521.28 ± 29.21 ABb 144.91 ± 5.97 Ba 103.14 ± 7.14 BCb 7 648.55 ± 24.70 Ba 497.95 ± 18.77 Bb 135.5 ± 2.76 BCa 118.30 ± 6.68 BCb 14 359.96 ± 17.28 Ca 261.94 ± 28.36 Cb 156.93 ± 3.50 Ba 103.87 ± 10.77 BCb 28 290.15 ± 18.59 Da 215.04 ± 9.89 Cb 135.75 ± 3.24 BCa 99.55 ± 7.96 BDa 42 193.22 ± 15.92 Ea 133.88 ± 5.40 Db 115.41 ± 2.04 Da 84.19 ± 3.41 Da

exclusion: F 1, 60 = 104.21, P < 0.001 exclusion: F 1, 60 = 94.07, P < 0.001 time: F 5, 60 = 207.96, P < 0.001 time: F 5, 60 = 194.32, P < 0.001 interaction: F 5, 60 = 3.31, P = 0.010 interaction: F 5, 60 = 8.86, P < 0.001 Late 2 829.21 ± 14.04 Aa 708.13 ± 13.42 Ab 301.64 ± 5.62 Aa 237.64 ± 2.86 Ab Season 4 702.10 ± 9.57 Ba 535.84 ± 10.21 Bb 217.66 ± 6.64 Ba 186.75 ± 1.55 Bb 7 741.68 ± 10.95 Ba 630.58 ± 7.10 Cb 220.30 ± 2.23 Ba 187.11 ± 2.11 Bb 14 712.34 ± 13.14 Ba 605.70 ± 9.85 Cb 227.27 ± 6.99 Ba 169.89 ± 3.89 Cb 28 442.28 ± 10.97 Ca 274.27 ± 10.31 Db 191.33 ± 2.80 Ca 115.69 ± 4.09 Db 42 293.96 ± 9.47 Da 219.38 ± 8.55 Eb 181.30 ± 3.79 Ca 117.21 ± 4.52 Db

exclusion: F 1, 60 = 398.59, P < 0.001 exclusion: F 1, 60 = 482.79, P < 0.001 time: F 5, 60 = 703.00, P < 0.001 time: F 5, 60 = 208.54, P < 0.001 interaction: F 5, 60 = 5.68, P < 0.001 interaction: F 5, 60 = 9.02, P < 0.001

56

Table 1 cont. The effects of age on degradation of physical and chemical

characteristics of dung pats with arthropod community exclusion/inclusion.

Capital letters represent differences over time and lower case letters represent

differences between treatments (α = 0.05).

Days Ash free organic matter Ash free organic matter

weight of dried dung (g) (% of dry weight)

Exclusion Inclusion Exclusion Inclusion Early 2 168.09 ± 3.63 Aa 116.57 ± 9.19 Ab 87.12 ± 1.21 Aa 79.20 ± 0.48 Ab Season 4 125.12 ± 6.06 Ba 80.83 ± 5.27 Bb 86.27 ± 1.49 ABa 78.52 ± 1.12 Ab 7 114.67 ± 1.90 BCa 92.32 ± 5.41 Bb 84.65 ± 0.60 ABa 78.01 ± 0.53 ABb 14 133.28 ± 3.11 Ba 79.51 ± 8.08 BCb 84.93 ± 0.69 ABa 76.60 ± 0.65 Bb 28 114.51 ± 3.07 BCa 74.13 ± 5.63 BCb 84.33 ± 0.27 Ba 74.61 ± 0.50 Ca 42 92.57 ± 1.72 Da 58.67 ± 2.32 Db 80.21 ± 0.53 Ca 69.70 ± 0.23 Db

exclusion: F 1, 60 = 182.80, P < 0.001 exclusion: F 1, 60 = 350.22, P < 0.001 time: F 5, 60 = 34.55, P < 0.001 time: F 5, 60 = 28.11, P < 0.001 interaction: F 5, 60 = 2.45, P = 0.044 interaction: F 5, 60 = 1.60, P = 0.175 Late 2 267.33 ± 6.44 Aa 204.23 ± 3.92 Ab 88.58 ± 0.59 Aa 85.91 ± 0.82 Ab Season 4 190.59 ± 5.55 Ba 158.49 ± 1.50 Bb 87.59 ± 0.53 ABa 84.87 ± 0.80 ABb 7 192.65 ± 1.83 Ba 158.61 ± 2.49 Bb 87.17 ± 0.46 ABCa 84.75 ± 0.96 ABa 14 197.65 ± 6.51 Ba 141.99 ± 2.91 Cb 86.95 ± 0.60 BCa 83.61 ± 0.85 Bb 28 164.24 ± 2.55 Ca 94.55 ± 3.17 Db 85.84 ± 0.42 Ca 81.76 ± 0.89 Cb 42 155.66 ± 2.85 Ca 93.63 ± 3.61 Db 85.88 ± 0.38 Ca 79.88 ± 0.47 Db

exclusion: F 1, 60 = 531.25, P < 0.001 exclusion: F 1, 60 = 144.60, P < 0.001 time: F 5, 60 = 205.94, P < 0.001 time: F 5, 60 = 20.26, P < 0.001 interaction: F 5, 60 = 8.23, P < 0.001 interaction: F 5, 60 = 3.49, P < 0.001 57

Table 2. Relationships of dung beetle abundance, richness, and diversity to the

arthropod community characteristics in inclusion dung pats throughout

grazing season. Statistical presentation are the result of linear regressions, and α

= 0.05

Dung beetle Characteristic Abundance Richness Diversity Early season Arthropod F1, 35 = 47.64, F1, 35 = 74.46, F1, 35 = 59.42, biomass (mg) P < 0.001 P < 0.001 P < 0.001 Arthropod F = 44.84, F = 15.07, F = 10.73, abundance 1, 35 1, 35 1, 35 P < 0.001 P < 0.001 P = 0.001 Species richness F1, 35 = 42.53, F1, 35 = 74.46, F1, 35 = 16.31, P < 0.001 P < 0.001 P < 0.001 Micro-coprophage abundance F1, 35 = 52.80, F1, 35 = 19.69, F1, 35 = 15.16, P < 0.001 P < 0.001 P < 0.001

Late season Arthropod biomass (mg) F1, 34 = 70.80, F1, 34 = 63.94, F1, 34 = 61.20, P < 0.001 P < 0.001 P < 0.001 Arthropod abundance F1, 34 = 27.23, F1, 34 = 30.00, F1, 34 = 27.54, P < 0.001 P < 0.001 P < 0.001 Species richness F1, 34 = 42.95, F1, 34 = 63.94, F1, 34 = 81.97, P < 0.001 P < 0.001 P < 0.001 Micro-coprophage richness F1, 34 = 25.06, F1, 34 = 28.65, F1, 34 = 28.31, P < 0.001 P < 0.001 P < 0.001 58

8.0 Figures

Fig. 1. Arthropod dry weight biomass (mean ± SEM) per cattle dung pat (n = 6) over the age of the pat. Arthropods were excluded from half of the pats (n = 6 pats per treatment per age) using cages. Pats were examined beginning in June (A) and in late July

(B). Asterisks above the bars indicate significantly different arthropod biomasses in the caged and uncaged pats for that specific sample age (α = 0.05).

Fig. 2. Arthropod abundance (mean ± SEM) per cattle dung pat (n = 6) over the age of the pat. Arthropods were excluded from half of the pats (n = 6 pats per treatment per age) using cages. Pats were examined beginning in June (A) and in late July (B).

Asterisks above the bars indicate significantly different arthropod abundances in the caged and uncaged pats for that specific sample age (α = 0.05).

Fig. 3. Degradation rate of organic matter content (mean ± SEM) in cattle dung pats. Dung pats were dried to 0% moisture and burned in furnace to remove all organic matter allowing calculation of ash-free organic matter content (AFOM). AFOM content was calculated in dung pats beginning in June (A) and late July (B). Half of pats had arthropods excluded (n = 6 pats per treatment per dung age) compared to allowing uninhibited arthropod colonization.

Fig. 4. Correlation of the diversity of dung beetles to total arthropod abundance in cattle dung pats. Dung beetle diversity (Shannon H) in dung pats was run in a linear regression to observe correlation to total arthropod abundance per individual cattle dung pat. Beginning in June (A) and late July (B) there was a significant and positive correlation between dung beetle diversity and the total arthropod abundance in dung pats that all species could freely colonize (n = 36 in both A and B).

59

Figure 1 .

60

Figure 2.

61

Figure 3.

62

Figure 4.

63

CHAPTER THREE: EFFECT OF CATTLE MANAGEMENT ON DUNG

ARTHROPOD COMMUNITY STRUCTURE.

Abstract:

Dung fauna plays a critical role in nutrient cycling and productivity of cattle- grazed pastures. We evaluated the effects that rangeland management systems (based on stocking density, rotation frequency, and number of avermectin applications) have on the dung arthropod community in eastern South Dakota ranches. Arthropod communities were collected from 16 cattle grazing operations in 2015-2016 using core samples of dung pats. Avermectin was quantified in pats from each ranch using enzyme-linked immunsorbant assay (ELISA). Arthropods in dung were abundant (116,244 specimens) and diverse in eastern South Dakota (172 morphospecies). Management systems with more regenerative practices (frequent rotation at high stocking densities and lack of avermectin applications) had arthropod communities with higher species richness, diversity, predator species abundance, and dung beetle abundance than more conventionally managed pastures. Avermectin quantity in the pats was negatively correlated with dung beetle abundance and diversity. Regenerative practices of high- intensity, frequent rotational grazing and eliminating prophylactic avermectin use can foster dung arthropod community structure, a key trait correlated with dung degradation and pest suppression on ranches.

64

1.0 Introduction

The costs and benefits of different cattle management strategies are regularly debated (Briske, Sayre et al. 2011, Norton, Barnes et al. 2013, Teague, Provenza et al.

2013, Roche, Cutts et al. 2015). In continuous season-long grazing systems, cattle live on a single pasture for the entire season. Continuous grazing systems are commonly implemented due to the ease with which a rancher can manage even large herds of cattle with minimal fencing work, water sources and transportation costs (Briske, Sayre et al.

2011). The benefits of this system must be weighed against the loss in long term productivity and sustainability of a pasture (Lodge 1970, Gillen, McCollum et al. 1998,

Briske, Derner et al. 2008). In continuously grazed pastures, cattle will often choose to graze some areas more heavily, spending a disproportionate amount of time in localized areas, while leaving others relatively untouched (Senft, Coughenour et al. 1987). A multi- paddock system where animals are grazed at high densities can lead cattle to graze more plant species within a pasture (Barnes, Norton et al. 2008). A key aspect of these high- density grazing systems is that herds are frequently moved, and the soil and plant community are allowed a regrowth and recovery period. This practice requires an understanding of the landscape and the local optimal plant regrowth rates, but results in higher forage quality in subsequent grazing periods (Teague, Provenza et al. 2013). In addition to fostering ecosystem services, higher quality forage associated with high intensity, multi-paddock grazing systems can support greater and faster weight gain and healthier animals (Walton, Martinez et al. 1981, Norton, Barnes et al. 2013).

There are a variety of pesticides and parasiticides that are used to manage internal and external pests of cattle; one of the most widely used is a group of chemicals called 65 avermectin. Avermectins came to dominate the livestock pesticide market due to their strong antihelminthic and insecticidal activity (Campell et al 1983). Five years after the advent of ivermectin (the most widely sold avermectin derivative), it was sold in 46 countries and administered to 320 million cattle (Campbell et al 1985); more recent estimates are that 56% of all U.S. cattle are administered avermectin (Omura and Crump

2004, Losey and Vaughan 2006). Avermectins are the result of fermentation of an actinomycete bacteria Streptomyces avermitilis , which is highly toxic to nematodes, but also insect pests (Burg, Miller et al. 1978).

Avermectins’ broad-spectrum toxicity to pest arthropods and nematodes may also pose hazards to non-target species on rangeland with treated cattle. A substantial portion

(80-98%) of administered avermectin is excreted in the dung (Alvinerie, Sutra et al. 1998,

Floate, Sherratt et al. 2005). Risk assessments have revealed that avermectins frequently reduce the populations of non-target dung arthropods, although risk posed by dung contamination depends on timing of application, method of administration, and concentration of the product administered (Wall and Strong 1987, Sommer et al 1992).

For example, sustained-release (SR)-bolus-administered avermectin residues in dung typically peak 3-4 days after treatment at levels as high as 4,100 ng per g of dung, and have a steady-state concentration of 1,180 ng per g for up to 120 d post-treatment

(Alvinerie, Sutra et al. 1998, Errouissi, Alvinerie et al. 2001, Suarez, Lifschitz et al.

2003). Avermectins used applied using other administration methods such as injections or topical applications are found at detectable levels in dung for a shorter duration (i.e., only several weeks) (Strong 1992, Halley, VandenHeuvel et al. 1993, Floate, Sherratt et al.

2005). Risk assessments on ivermectin’s toxicity to dung beetles have shown that 66 ivermectin levels present in dung are toxic to larvae of the dung beetles Aphodius constans (LC 50 : 470-780 ng per g of dung), A. fimetarius (LC 50 : 540 ng per g) and

Volinus distinctus (LC 50 : 500-620 ng per g) (Errouissi, Alvinerie et al. 2001, Hempel,

Scheffczyk et al. 2006, Lumaret, Alvinerie et al. 2007, Rombke, Coors et al. 2010). Sub- lethal effects, such as extended larval development or decreased larval size, occur at even lower levels (O’hea et al 2010). Values for the lowest observed effect concentration

(NOEC) to dung beetle larvae range from 38-310 ng per g of dung (Errouissi, Alvinerie et al. 2001, Hempel, Scheffczyk et al. 2006). These affected communities have reduced ecological function within treated pastures; dung pats often degrade more slowly, sometimes taking years when avermectins are heavily applied to livestock (Wall and

Strong 1987, Madsen, Overgaard Nielsen et al. 1990, Strong 1992, Herd 1995, Dadour,

Cook et al. 1999, Rombke, Coors et al. 2010). Ivermectin levels of 780 ng per g (dry weight dung) and higher were found to significantly slow the decomposition rate of dung pats.

This study takes a systems level approach on rangeland management to establish the relative effects of management system on the dung arthropod community. Using this approach, we observed typical cattle operations with manager imposed practices to determine what impact would be seen by the dung arthropod community. The dung arthropod community structure was recorded and characteristics of the community were compared to see if there were any differences among regenerative, intermediate, and conventionally managed systems (defined based on a suite of practices). The effect that avermectin has on the arthropod community and specifically beneficial arthropod groups was examined to identify ecological costs of avermectin use. This information can help 67 ranchers make informed decisions regarding how their management decisions affect the financial and ecological contributions of dung arthropod communities to their operations.

We hypothesize that management systems that implement a more regenerative set of practices will impact the dung arthropod community positively. We also hypothesize that the frequency of avermectin product use will negatively affect the arthropods colonizing cattle dung pats.

2.0 Materials and Methods

2.1 Experimental design . Sampled cattle operations (n = 16; 10 in 2015 and six in

2016) represented a variety of cattle management practices in eastern South Dakota. The

16 cattle operations span 7,935 km 2 across eastern South Dakota. All sites were grazed by cattle for at least 5 y, but annual grazing intensity and grazing period varied. Herds ranged from 20 to 120 individuals, and the cattle differed in size, breed, and the administered avermectin products. The systems were ranked from regenerative to conventional based on several practices (Table 1). In our study, the designation of management systems was based upon the grouping of several management practices that were sometimes all present on the same cattle operation. This grouping approach was based on findings that these practices’ impact the rangeland ecosystem and specifically the dung arthropod community (Senft, Rittenhouse, and Woodnansee 1985, Lumaret,

Alvinerie et al. 2007, Errouissi and Lumaret 2010, Norton, Barnes et al. 2013, Teague et al. 2013, Verdu, Cortez et al. 2015). The three management systems used throughout the study were designated as regenerative (n = 5 operations), intermediate (n = 5 operations), and conventional (n = 6 operations). These management systems were divided by three of 68 the practices with either most importance to rangeland management or potential to impact dung arthropods. These practices were stocking density, rotation frequency, and use of avermectin products and the cattle operations were categorized based upon their combination of these practices to form the different systems. Use of avermectin in the ranches was categorized as high (multiple applications during a year; scored as 0), low

(single annual use, not applied during grazing period; scored as 1) and no avermectin

(scored as 2). Operations’ stocking densities (animal units [AU] per ha), were categorized as fewer than 5 animal units (AU) per ha (scored as 0), 5-10 AU per ha (scored as 1), and more than 10 AU per ha (scored as 2). Operations were categorized as having a rotation frequency of 30 d or more (scored 0), between 10-30 d (scored as 1), and less than 10 d

(scored as 2). Ranches with the top 33% of scores were considered regenerative, the middle 33% of scores were intermediate, and the lowest third of scores was considered conventional.

2.2 Sampling procedure. Each of the ranches was sampled monthly from May to

September. Two- to 5-d old dung pats (n = 10 per ranch) were randomly selected from each ranch; this age of pat has peak arthropod abundance and diversity (Kessler and

Balsbaugh 1972, Lee and Wall 2006). Chapter II showed that after the initial first 2 days of colonization the arthropod abundance plateaus until the dung pat ages 7 days on the pasture surface. Preliminary work showed that dung arthropod communities present in dung pats during this window of time are consistent (Chapter II); ranchers kept records of when the cattle were moved from a sampled pasture to help us target pats within this age range. A core (10 cm diameter, 10 cm deep) was collected from each selected pat, and the arthropods within each pat was extracted using a Berlese system over 7 d, at that point 69 preliminary experiments showed that the core had completely dried and all arthropods had left the dung pat. Arthropods from each core were stored in 70% ethanol. All extracted arthropods were identified microscopically and cataloged; each unique specimen was identified to the lowest taxonomic level possible representing a functional morphospecies. Each morphospecies was placed into a trophic guild (coprophage, predator, parasitoid, herbivore, or pest) based upon previous descriptions of the biology of arthropod community in dung pats (Mohr 1943, McDaniel, Boddicker et al. 1971,

Cervenka and Moon 1991).

2.3 Avermectin ELISA . The amount of avermectin in dung pats was quantified using a direct, competitive enzyme-linked immunosorbent assay (ELISA) and following kit instructions (Product #5142B, Abraxis, Warminster, PA). A 500 μL (approximately

0.65 ± 0.02 g; mean ± SEM) sample was collected from five of the dung pats per field.

This sample was vortexed with 100 μL of water and 100 μL of ethanol for 1 min. The mixture was centrifuged at 14,000 g for 2 min and 50 μL of the resulting supernatant was analyzed. Absorbance values at 450 nm were recorded for each well on 96-well plates

(μQuant, Biotek Instruments, Winooski, VT). To quantify ivermectin in the dung samples, a standard curve series with concentrations of 1, 0.5, 0.25, 0.1, 0.05, 0.025, and

0.01 ng avermectin/μL dung was included on each plate. Additionally, a negative control series of 0 ppm ivermectin was included in three wells on each plate. To distinguish positive samples from background absorbance of the matrix, the mean and standard deviation of the negative control series were calculated for each plate; any samples with a lower optical density (direct competitive ELISAs have an absorbance negatively 70 associated with avermectin concentration) than the mean minus three times the standard deviation of this series were considered positive for avermectin.

2.4 Data Analysis. All statistics were conducted using Systat 13 and SigmaPlot 13 software (SYSTAT Software, Inc; Point Richmond, CA). Two-way ANOVAs were used to investigate how month and management system will impact arthropod community characteristics of abundance, species richness, and species diversity as well as their effect on arthropod functional groups of coprophages, predators, herbivores, and parasitoids.

Month and pasture qualities effect on avermectin content in dung was also observed.

Linear regressions were generated to compare the quantity of avermectin found in dung to arthropod abundance, species richness, and diversity as well as the abundance of beetle larvae and members of Scarabaeidae.

3.0 Results

3.1 Description of dung arthropod community. In sum, 116,244 arthropod specimens were identified representing 172 morphospecies. These species were represented by six classes of arthropods across 14 orders (Acarina, Araneae, Coleoptera,

Collembola, Diptera, Hemiptera, Hymenoptera, Isopoda, Julida, Lepidoptera,

Lithobiomorpha, Protura, Pseudoscorpiones, and Thysanoptera). Due to the difference in ecological function of larvae and adults, larvae were considered distinct morphospecies.

The highest number of morphospecies were Coleoptera adults, Hymenoptera, Coleoptera larvae, Diptera adults, and Araneae containing 79, 24, 16, 14, and 11 morphospecies, respectively. The most abundant groups collected were Acarina (43,757), Coleoptera adults (24,945), Diptera larvae (17,988), Collembola (13,324), and Hymenoptera (6,610) 71

. All species collected were divided trophically into coprophages (74,703 individuals representing 53 morphospecies), pests (20,282 individuals representing 21 morphospecies), predators (18,861 individuals representing 54 morphospecies), herbivores (2,159 individuals representing 27 morphospecies), and parasitoids (239 individuals representing 17 morphospecies). Across all 16 ranches there was an average species richness of 34.76 ± 0.85 (mean ± SEM) species found per site per month with an overall average diversity (Shannon H) of 2.07 ± 0.04. In total 18,501.02 ± 1,385.18 arthropods were found per m 2 of cattle dung throughout the study. A complete breakdown of arthropod specimens can be seen in Table 2.

3.2 Dung community over time and pasture quality. Arthropod communities in dung changed over the summer and were different among the range management systems. The number of arthropods differed among months of the season, but abundance was not affected by our range management systems (month: F 4, 65 = 4.38, P = 0.003; management: F2, 65 = 0.34, P = 0.72; interaction: F 8, 65 = 0.24, P = 0.98). Species richness was significantly affected by both time of season and management system

(month: F4, 65 = 6.94, P < 0.001; management: F 2, 65 = 10.69, P < 0.001; interaction: F8, 65 = 1.89, P = 0.08). Arthropod abundance started low in May

(8,815.69 ± 1,034.38 arthropods per m 2); the remaining months were indistinguishable from each other, but had significantly more arthropods than were found in May. Species richness was similarly lowest in May; the remaining months had significantly more arthropods than in May, but the remaining season did not vary statistically. Management system had a significant effect on the diversity of arthropods, but month did not

(month: F4, 65 = 1.38, P = 0.25; quality: F 2, 65 = 7.77, P = 0.001; interaction: F 8, 65 = 0.54, 72

P = 0.82) (Fig. 2). Species richness and diversity were found to be significantly lower in pastures with continuous rotation, lower stocking densities and high avermectin use compared to the more regenerative systems. Systems with the most regenerative practices had a species richness of 38.24 ± 1.19 species per site per month sampled versus

31.03 ± 1.35 in the conventional system; diversity in regenerative systems was

2.24 ± 0.06, and 1.90 ± 0.05 in conventional systems. Predator abundance was significantly affected by month and management system (month: F4, 65 = 3.58, P = 0.01; management: F 2, 65 = 3.71, P = 0.03; interaction: F 8, 65 = 0.28, P = 0.97). Pastures managed conventionally had significantly fewer predators than the more regenerative ranches. Month sampled had a significant effect on parasitoid abundance, while management system did not (month: F4, 65 = 3.65, P = 0.009; management: F 2, 65 = 1.10, P

= 0.30; interaction: F 8, 65 = 0.48, P = 0.87). The months of May, August, and September had significantly fewer parasitoids than June or July. Herbivore abundance was not significantly affected by sampling month or management system (month: F4, 65 = 1.39, P

= 0.25; management: F 2, 65 = 1.21, P = 0.23; interaction: F 8, 65 = 0.41, P = 0.83).

Abundance of the entire coprophage assemblage was found to be significantly affected by month sampled but not by management system (month: F4, 65 = 3.88, P = 0.007; management: F 2, 65 = 0.218, P = 0.81; interaction: F 8, 65 = 0.30, P = 0.96). Management systems but not month sampled had a significant effect on maggot populations

(month: F4, 65 = 2.31, P = 0.06; management: F 2, 65 = 2.87, P = 0.047; interaction:

F8, 65 = 0.59, P = 0.79).

Dung beetle abundance was significantly affected by the pasture’s management system, but no differences were seen among months (month: F4, 65 = 1.86, P = 0.13; 73

quality: F2, 65 = 9.06, P < 0.001; interaction: F 8, 65 = 0.69, P = 0.70). Regenerative pastures, with frequent rotations, high stocking densities and no avermectin use, had significantly more dung beetles (827.52 ± 140.63 beetles per m 2 of dung) than conventionally managed pastures (267.09 ± 65.30 dung beetles per m 2). The diversity of dung beetles was significantly affected by both month and management system

(month: F4, 65 = 5.52, P = 0.001; management: F 2, 65 = 6.83, P = 0.002; interaction:

F8, 65 = 1.37, P = 0.23). The most numerous dung beetle species were Aphodius haemorrhoidalis (n = 1396), A. rubeolus (n = 476), A. erraticus (n = 363), A. fossor

(n = 299), Onthophagus Hecate (n = 223), and A. fimetarius (n = 130). While the overall abundance of dung beetles was not significantly different over the season, the individual species had significant changes over time. Aphodius fossor and A. erraticus were found at

12-13 of the 16 ranches in the May and June sampling dates and by August fewer than three ranches contained either of the two species. Inversely, A. fimetarius was found on only one ranch in May and nine ranches in September. Aphodius rubeolus was found in

14-15 ranches in June, July, and August while in May and September only six ranches had any A. rubeolus. Aphodius haemorrhoidalis and O. hecate were found consistently across the entire sampling period.

3.3 Avermectin ELISA quantification. The average avermectin in cattle dung pats across all 16 ranches was found to be 187.56 ± 19.25 ng of avermectin per mL of dung.

The amount of avermectin (ng/mL of dung) was found to be significantly affected by the month sampled and the management system (month: F4, 65 = 3.08, P = 0.02; management:

F2, 65 = 55.36, P < 0.001; interaction: F 8, 65 = 1.69, P = 0.12) (Fig. 1). Avermectin in May was significantly higher than all other months except September, and avermectin quantity 74 in September similar to that found in every month but May. Management systems had significantly different quantities of avermectin found in dung pats. The most conventionally managed systems had the highest avermectin contamination, with

329.79 ± 29.59 ng/ml. Intermediately managed systems had half the 180.66 ± 21.16 ng/ml and the regeneratively managed pastures had only 23.78 ± 7.31 ng/ml of dung.

3.4 Avermectin correlations to arthropod metrics. Avermectin in dung pats influenced many aspects of the arthropod community. While the entire community abundance was not correlated to avermectin (F1, 78 = 3.21, P = 0.08), there was a negative correlation of species richness (F1, 78 = 21.90, P < 0.001), and species diversity

(F1, 78 = 7.06, P = 0.01). There was no correlation to avermectin and coprophagous arthropods, (F1, 78 = 2.36, P = 0.13); however predatory species were negatively correlated to higher avermectin quantities (F1, 78 = 6.93, P = 0.01) (Fig. 3). Dung beetles were negatively correlated with higher avermectin levels in dung (F1, 78 = 18.13,

P < 0.001) as were larvae of all Coleopteran (F1, 78 = 5.46, P = 0.022). Maggot abundance was positively correlated to a higher avermectin content in dung pats (F1, 78 = 4.21,

P = 0.047). Maggot response to management practices will be discussed at greater length in Chapter IV.

4.0 Discussion

Ranchers that abandoned avermectins often used a high-density and frequently- rotated grazing system. Categorizing the management system according to a range of practices was necessary to fully understand the effects of management on the arthropod community. Management system significantly influenced the dung arthropod 75 communities found in these rangelands. Regenerative systems had 19% more species and

16% greater diversity (Shannon H) than the conventionally managed pastures. These losses in community structure may limit the ability of the community to provide ecosystem services (Hooper, Chapin et al. 2005, Wagg, Bender et al. 2014, Manning,

Slade et al. 2016). Dung beetles are a major driver of community diversity and function, and their abundance was significantly reduced in conventionally managed systems. Two inter-related differences in these management systems may have driven community patterns: grazing intensity and avermectin use.

Our study revealed a diverse community of arthropods in cattle dung that changes seasonally. In total, 172 unique morphospecies were found in dung from eastern

South Dakota (Table 2). This species richness was comparable to other studies of dung communities, where 108-275 species have been recovered (Cervenka and Moon 1991,

Skidmore 1991). Dung pats were sampled from the months of May through September, representing most of the grazing season in the region. Arthropod abundance and species richness were lowest in May with all following months containing significantly higher values but not distinguishable from one another. This “lag time” in community growth may be partially explained because pats in May have the highest avermectin residues.

The effects of avermectin on communities will be discussed later (Fig. 1). There was little observed change in abundance metrics across the months sampled but the composition of communities changed throughout the season. For example, overall dung beetle abundance was not significantly different over the summer but diversity varied substantially over the season. Not only this, but different species were only found during certain parts of the growing season. Even within the genus Aphodius , we found distinct 76 seasonal shifts in which species dominated the community of dung pats. Seasonality of dung arthropods has been discussed in the past, questioning how so many different species can be supported throughout the season by a single discrete resource (Hanski and

Koskela 1977, Hanski 1980). These studies on the seasonal occurrence of dung- inhabiting beetles show that subtle seasonal separations, while not altering overall abundance within the guild of dung beetles, is enough to relieve competitive pressure from the system. Dung may support such a diverse community because the rapid renewal of the primary resource. Even though dung represents an attractive resource, not all the

172 morphospecies found in the dung pat system are coprophagous. There were many predator, herbivore, and parasitoid species found that all respond to the dung resource for reasons other than simply feeding on the pat itself. Even within coprophagous arthropods there are different species that partition the dung resource based on moisture content, fiber content, and particle size of the dung (Holter and Scholtz 2007, Tixier, Lumaret et al. 2015, Holter 2016). The different reproductive and overwintering strategies among species further contribute to when dung taxa dominate the community (Gittings and

Giller 1997). All of this is to say that multiple factors influence the species observed in a single snapshot of the dung community, and ultimately may contribute to the function of this important group of insects.

The cattle grazing practices of stocking density and rotation frequency may affect dung arthropods in several ways. First, changes in forage diversity, quantity, and quality affect the relative nutrition/composition of dung pats (Van Vurren and Meijs 1987).

Grazing patterns alter resources available to cattle within a pasture with rotational grazing leading to more homogenous grazing, and less bare ground within the pasture over a four 77 year period (Jacobo, Rodriguez et al. 2006). In addition to changing the diversity and biomass of forage, plants from pastures that are grazed intensively and then allowed to rest are higher in calcium, magnesium and crude protein (Walton, Martinez et al. 1981,

Earl and Jones 1996, Barnes, Norton et al. 2008, Teague, Provenza et al. 2013). These changes in nutrition of the forage affect dung pat composition, and can lead to a more attractive resource for dung beetles and other dung arthropods (Holter and Scholtz 2007).

Another explanation that may have driven the greater arthropod abundance and diversity in regenerative systems is the relative concentration of dung within a pasture. High stocking density produces a concentration of dung resources that may have been relatively more attractive to dung arthropods (Finn and Gittings 2003, Dormont, Epinat et al. 2004). High stocking density also likely increases trampling that might alter the physical characteristics of the dung, perhaps making it more easily accessible to a greater number of dung arthropod species (Merritt and Anderson 1977, Strong 1992). Some or all of these factors likely influenced the dung as a resource in the regenerative and conventional systems.

One of the factors associated with the regenerative designation of the pasture was the reduced reliance on avermectin in the system. Avermectins are touted for their ability to control arthropod pests, however this efficacy comes with risks to non-target species

(Wall and Strong 1987, Strong 1992, Verdu, Cortez et al. 2015). Each site had dung avermectin residues quantified throughout the season and higher quantities were found in systems that administered avermectins more frequently (Fig. 1). Avermectin levels collected from conventionally managed ranches were often within the range where lethal or sub-lethal effects could be experienced by dung beetle larvae (Hempel, Scheffczyk et 78 al. 2006, Rombke, Coors et al. 2010). The toxicity of avermectin, coupled with its insect- repellent properties, can disrupt community structure (Floate 2007, Webb, Beaumont et al. 2010). The loss structure and complexity within an arthropod community can lead to a failure to provide ecosystem services of dung degradation (Chapter II) and pest suppression (Chapter IV).

Dung beetles were likely an important driver of the relative abundances of other dung taxa in these different management systems. In systems with the most conventionally managed pastures and highest avermectin use, there were 66% fewer dung beetles than the regenerative pastures. This lower abundance not only represents a decrease of an important coprophagous group, but dung beetles’ multifunctionality and role as a keystone species (Chapter II) means that fewer numbers may have knock on effects on the remaining arthropod community. Dung beetles facilitate dung pat degradation and pest suppression (Fincher 1981, Lee and Wall 2006, Losey and Vaughan

2006). Dung beetles are early colonizers to dung pats, and their large body allows them to make tunnels and aerate pats; these tunnels then facilitate colonization by other species

(Sanders and Dobson 1966). Dung beetles, along with other coprophagous arthropods, directly compete with cattle parasites and pests for the dung resource (Doube 1990,

Ridsdill-Smith and Edwards 2011). Dung pats with a network of beetle-formed tunnels open pathways whereby predators can infiltrate the pats; these perforated pats produce fewer pest maggots (Valiela 1969, Valiela 1969). In conventional systems both predators and dung beetles were significantly fewer compared to the regenerative systems (Fig. 3).

If a management system reduces dung beetles, then the ecosystem services that they provide could be reduced as well, furthering a reliance on chemical products that come at 79 an ecological and economic cost to the rancher. By implementing regenerative practices, a rancher can provide a food source and habitat for thousands of arthropods that increase the profitability and natural resource base of a ranching operation.

5.0 Acknowledgements

Authors thank Michael Bredeson, Claire Bestul, Dakotah Grosz, Kae Januschka,

Nathan Koens, Marti La Vallie, Amy Lieferman, Abigail Martens, Alexander Nikolas,

Greta Schen, and Kassidy Weathers for their assistance in collecting, extracting, and sorting of insect specimen. Special thanks as well to Mark Longfellow in assisting with insect identification and all participating ranchers for their time and use of their pasture.

Ecdysis Foundation and NCR-SARE, via student research grant GNC15-207, funded this research.

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88

7.0 Tables

Table 1. The categorization of ranches (n = 16) sampled during the study. The combination of management practices was used to designate the ranch system.

Management practices of cattle operations were scored 0-2 based on regenerative nature of the practice with higher number indicating a more positive regenerative practice.

Avermectin application frequency was divided into multiple applications (0), single application not during grazing season (1), and no avermectin use (2). Stocking density was divided into <5 AU/ha (0), 5-10 AU/ha (1), and >10 AU/ha (2). Rotation frequency was divided into >30 d rotation (0), 10-30 d rotation (1), and <10 d rotation (2).

Location Year Stocking System Avermectin Rotation frequency (closest town) surveyed density designation Bruce, SD 2016 1 0 0 Conventional Castlewood, SD 2016 1 2 1 Intermediate Clear Lake, SD 2015 2 2 2 Regenerative Estelline, SD 2015 1 1 1 Intermediate Estelline, SD 2016 1 1 0 Conventional Flandreau, SD 2015 0 0 0 Conventional Gary, SD 2016 2 2 2 Regenerative Goodwin, SD 2016 2 2 2 Regenerative Madison, SD 2015 0 1 1 Conventional Milbank, SD 2015 1 1 1 Intermediate Milbank, SD 2015 0 0 0 Conventional Sioux Falls, SD 2015 2 2 2 Regenerative Summit, SD 2016 1 1 1 Intermediate Thomas, SD 2015 1 1 2 Intermediate Twin Brooks, SD 2015 2 2 1 Regenerative Volga, SD 2015 1 0 0 Conventional

89

Table 2. Arthropod community inhabiting dung pats during summer grazing seasons in 2015 and 2016. The mean ± SEM of each morphospecies collected is listed per meter square in the top 10 cm of the dung pat and underlying soil. A total of 116,244 arthropods were collected across 16 different pastures sampled.

Abundance per m2 dung Order Family Species (mean ± SEM)

Acarina Acarina Acarina spp. 6964.14 ± 351.24

Araneae Araneae Species 1 8.59 ± 14.10

Species 2 3.98 ± 9.25

Species 3 3.34 ± 3.92

Species 4 1.11 ± 0.00

Species 5 0.95 ± 2.01

Species 6 2.07 ± 1.30

Species 7 1.27 ± 1.70

Species 8 0.64 ± 0.00

Species 9 1.27 ± 1.70

Species 10 1.59±0.00

Species 11 0.48±0.00

Opiliones Phalangiidae Phalangiid spp. 3.34±0.00

Pseudoscorpionida Pseudoscorpionida Pseudoscorpion spp. 1.27±0.00

Collembola Collembola Collembola spp. 2120.58±171.58

Diplura Diplura Species 1 56.02±10.88

Species 2 68.44±20.78

Protura Protura Protura spp. 0.32±0.00

Isopoda Armadillidium Armadillidium spp. 3.18±6.26

Lithobiomorpha Lithobiidae Lithobiidae spp. 7.80±1.97 90

Diplopoda Diplopoda Diplopoda spp. 7.32±3.98

Thysanoptera Thysanoptera Thysanoptera spp. 6.53±5.86

Hemiptera Aphidae spp. 8.75±14.11

Anthocoridae Anthocoris sp. 1 0.64±0.00

Anthocoris sp. 2 0.48±3.18

Orius insiduosis 0.32±0.00

Cicadellidae Species 1 0.48±0.00

Species 2 0.80±2.25

Immature Hemiptera spp. 11.46±49.67

Lepidoptera larvae Lepidoptera larvae Species 1 304.78±243.49

Species 2 0.48±0.00

Species 3 0.16±0.00

Species 4 0.16±0.00

Species 5 0.16±0.00

Diptera Anisopodidae Sylvicola spp. 18.30±41.78

Muscidae Musca autumnalis 16.39±28.70

Haematobia irritans 30.72±9.77

Scathophagidae Scathophaga 77.51±128.72 stercoraria Sepsidae Species 1 1.11±0.00

Species 2 0.80±9.55

Species 3 0.48±3.18

Stratiomyidae Species 1 0.80±9.55

Species 2 0.80±3.18

Undetermined Diptera Species 1 0.64±2.60

Species 2 0.80±2.25

Species 3 0.48±0.00

Species 4 0.80±2.25 91

Species 5 0.64±2.60

Diptera larvae Muscidae larvae Species 1 1580.25±149.82

Species 2 823.31±109.69

Species 3 125.57±95.90

Species 4 0.16±0.00

Scathophagidae larvae spp. 189.24±366.95

Sepsidae larvae spp. 357.94±99.70

Diptera pupae Undetermined pupae spp. 1.27±9.37

Coleoptera Cantharidae Chauliognathus 0.32±0.00 pennsylvanicus Carabidae Harpalus sp. 1 2.07±3.04

Agonum sp. 1 0.95±0.00

Chrysomelidae Species 1 0.64±2.60

Curculionidae Species 1 1.43±8.05

Species 2 0.32±0.00

Species 3 0.16±0.00

Elateridae Species 1 0.48±0.00

Species 2 0.48±3.18

Species 3 0.80±2.60

Histeridae Hister abbreviatus 35.33±6.42

Undetermined sp. 1 0.16±0.00

Undetermined sp. 2 0.80±2.60

Hydrophilidae Sphaeridium latum 70.35±11.18

Sphaeridium 198.94±26.45 scarabaeodies

Sphaeridium 9.07±11.51 bipustulatum

Cryptopleurum 40.90±12.59 minutum Cercyon quisquilius 381.97±59.69 92

Cercyon analis 327.38±34.18

Cercyon 186.53±59.03 unipunctatus Cercyon 117.30±28.73 haemorrhoidalis

Cercyon lateralis 48.22±20.72

Cercyon terminatus 34.22±16.79

Cercyon pygmaeus 32.63±16.73

Undetermined sp. 1 2.23±7.89

Undetermined sp. 2 0.32±0.00

Undetermined sp. 3 0.32±0.00

Undetermined sp. 4 0.48±3.18

Undetermined sp. 5 0.32±0.00

Meloidae Species 1 0.48±3.18

Nitidulidae spp. 0.16±0.00

Ptiliidae spp. 621.98±72.61

Scarabaeidae Aphodius fossor 47.59±4.50

Aphodius erraticus 57.77±8.02

Aphodius rubeolus 75.76±28.43

Aphodius 222.18±22.17 haemorrhoidalis

Aphodius terminalis 6.84±6.87

Onthophagus hecate 35.49±4.77

Onthophagus 3.18±10.21 pennsylvanicus

Tomarus relictus 0.32±0.00

Aphodius 20.69±2.57 fimertarius

Aphodius carri 1.59±3.68 93

Aphodius 0.64±0.00 stercorosus

Aphodius concavus 1.11±15.92

Euphoria inda 0.16±0.00

Aphodius granarius 9.87±22.68

Eucanthus lazarus 0.16±0.00

Onthophagus 0.80±2.60 orpheus

Aphodius lividus 0.32±0.00

Aphodius russeus 0.16±0.00

Aphodius kirni 0.80±2.60

Staphylinidae Species 1 1127.14±58.52

Species 2 5.89±3.66

Species 3 60.48±5.69

Species 4 9.07±2.73

Species 5 31.04±23.88

Species 6 42.02±7.29

Species 7 0.16±0.00

Species 8 4.62±6.69

Species 9 47.27±8.39

Species 10 0.48±3.18

Species 11 2.07±0.00

Species 12 6.84±7.01

Species 13 5.09±2.71

Species 14 3.98±9.02

Species 15 13.53±3.68

Species 16 0.32±0.00

Species 17 0.80±2.25 94

Undetermined Coleoptera Species 1 3.98±28.39

Species 2 0.32±0.00

Species 3 1.11±1.84

Species 4 0.64±0.00

Species 5 0.16±0.00

Coleoptera larvae Carabidae larvae Species 1 55.55±5.69

Elaterid larvae Species 1 2.55±1.63

Species 2 3.98±3.94

Species 3 8.28±2.44

Histeridae larvae spp. 13.69±11.40

Hydrophilidae larvae Sphaeridium sp. 216.29±13.57

Species 1 0.32±0.00

Species 2 1.43±0.00

Scarabaeidae larvae Species 1 10.19±5.81

Species 2 0.32±0.00

Species 3 0.80±0.00

Staphylinidae larvae Species 1 259.42±32.58

Undetermined larvae Species 1 47.91±39.58

Species 2 4.30±23.44

Species 3 1.11±15.92

Species 4 0.48±0.00

Hymenoptera Formicidae Lasius neoniger 839.22±196.53

Ponera sp. 1 10.35±47.30

Formicia sp. 1 149.92±97.85

Formicia sp. 2 8.75±47.67

Formicia larvae sp. 5.73±40.01 1 95

Parasitoids Parasitoid 1 1.75±1.42

Parasitoid 2 5.41±7.00

Parasitoid 3 1.59±2.41

Parasitoid 4 15.76±6.55

Parasitoid 5 0.64±0.00

Parasitoid 6 0.32±0.00

Parasitoid 7 0.32±0.00

Parasitoid 8 0.32±0.00

Parasitoid 9 3.18±3.95

Parasitoid 10 0.95±2.01

Parasitoid 11 3.66±4.49

Parasitoid 12 0.80±0.00

Parasitoid 13 0.80±0.00

Parasitoid 14 0.64±0.00

Parasitoid 15 0.48±3.18

Parasitoid 16 0.32±0.00

Parasitoid 17 0.64±0.00

Parasitoid 18 0.32±0.00

Parasitoid 19 0.16±0.00

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Table 3. Arthropod community characteristics of dung pats during summer grazing seasons in 2015 and 2016. The mean ± SEM of each community characteristic was taken across the three management systems per month. Management practices of cattle operations were scored 0-2 based on regenerative nature of the practice with higher number indicating a more positive regenerative practice. Avermectin application frequency was divided into multiple applications (0), single application not during grazing season (1), and no avermectin use (2). Stocking density was divided into <5

AU/ha (0), 5-10 AU/ha (1), and >10 AU/ha (2). Rotation frequency was divided into >30 d rotation (0), 10-30 d rotation (1), and <10 d rotation (2). Sum of these scores yielded a regenerative level for each operation. Letters represent difference across the management systems (α = 0.05).

Arthropod Regenerative Intermediate Conventional community Statistics systems systems systems characteristics Arthropod F = 0.34, abundance 18,686.37 ± 2,864.94 19,795.67 ± 2,165.32 17,292.14 ± 1,912.13 2, 65 P = 0.72 (per m 2) F = 0.218, Coprophages 14,711.85 ± 2,422.47 16,213.50 ± 1912.13 14,562.21 ± 1,707.83 2, 65 P = 0.81 F = 3.71, Predators 3,561.27 ± 494.34 A 3,375.29 ± 280.74 A 2,228.45 ± 386.72 B 2, 65 P = 0.03 F = 1.10, Parasitoids 40.76 ± 9.27 34.65 ± 6.84 38.64 ± 11.47 2, 65 P = 0.30 F = 1.21, Herbivores 372.48 ± 245.90 172.l23 ± 61.85 462.85 ± 401.24 2, 65 P = 0.23 F = 9.06, Dung beetles 827.52 ± 140.63 A 406.11 ± 78.72 B 267.09 ± 65.30 C 2, 65 P < 0.001 Species F = 10.69, 38.24 ± 1.19 A 35.76 ± 1.52 A 31.03 ± 1.35 B 2, 65 richness P < 0.001 F2, 65 = 7.77, Diversity 2.24 ± 0.06 A 2.09 ± 0.06 A 1.90 ± 0.05 B P = 0.001 F = 3.14, Evenness 0.62 ± 0.02 A 0.59 ± 0.01 AB 0.56 ± 0.01 B 2, 65 P = 0.05

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8.0 Figures

Fig. 1. Avermectin found in 2- to 5-d old dung pats (mean ± SEM) over months sampled in different regenerative quality pastures (n = 16) from 2015-2016.

Avermectin quantity found in dung pats using ELISA and plotted over the grazing season and divided by management systems: regenerative (frequent rotation, high stocking density, low/no avermectin use), intermediate (moderate rotation, medium stocking density, low avermectin use), and conventional (continuous grazing, low stocking density, multiple avermectin applications).

Fig. 2. Species richness and diversity of dung arthropod community in eastern

South Dakota ranches (n = 16) under different management practices. S pecies richness (A) and diversity (B) were averaged (mean ± SEM) across dung pats sampled from May-September and divided by management systems: regenerative (frequent rotation, high stocking density, low/no avermectin use), intermediate (moderate rotation, medium stocking density, low avermectin use), and conventional (continuous grazing, low stocking density, multiple avermectin applications). Different letter over bar indicates significantly different community characteristic between pasture qualities (α =

0.05).

Fig. 3. Correlation between the abundance of different dung arthropod functional groups and the amount of avermectin found in dung. Abundance of dung beetles (A) and predators (B) found in dung pats across ranches (n = 16) in 2015-2016 was run in a linear regression to observe the correlation to the amount of avermectin (ng per mL of dung). There was a significant and negative correlation between both functional groups and avermectin (α = 0.05). 98

Figure 1. 99

Figure 2. 100

Figure 3.

101

CHAPTER FOUR: THE INFLUENCE OF CATTLE MANAGEMENT SYSTEMS

ON PEST MAGGOT POPULATIONS IN SOUTH DAKOTA

Abstract:

Cattle dung pats in rangelands provide pest maggots with a food source and habitat to proliferate and cause economic problems to the cattle operation. We evaluated the relative dung arthropod communities and maggot populations on ranches categorized as regenerative, intermediate, and conventional management systems based on their stocking density, rotation frequency, and number of avermectin applications. Arthropod communities were collected from 16 ranches using core samples of dung pats, and an exclusion cage study was used to describe maggot population growth with reduced predators and competitors. Maggots made up 19,338 of the 116,244 arthropod specimens collected in this study, and there were significantly fewer maggots found in the regenerative rangeland system (1,990.32 ± 239.75 per m 2) versus the intermediate

(3,457.33 ± 542.98 per m 2) and conventional (3671.76 ± 689.19 per m 2) systems.

Maggot abundance was positively correlated with avermectin levels found in the dung.

Exclusion cages demonstrated the importance of dung arthropod communities in restricting maggot population growth. Regenerative systems had fewer maggots per predator and coprophagous competitor compared to conventionally managed pastures.

This work demonstrates that regenerative management practices that foster dung arthropod communities can reduce the insecticide inputs needed for maggot control.

102

1.0 Introduction

Cattle dung functions as a food source and a microhabitat for a variety of arthropod species. From the time of deposition, dung pats provide a “hot spot” where arthropod abundance is higher than what is found in the surrounding pasture (Errouissi,

Haloti et al. 2004). As a pat ages, the arthropod community composition changes in response to the size, moisture, and nutrient content of the pat (Koskela and Hanski 1977,

Yamada, Imura et al. 2007, Chapter II). The successional changes in arthropod communities in response to pat characteristics leads to a dynamic community (Mohr

1943, Sanders and Dobson 1966, Valiela 1969). Changes in arthropod communities in dung pats have even been described in South Dakota, an area of the country dominated by agricultural production (McDaniel, Boddicker et al. 1971, Kessler and Balsbaugh

1972). Bioinventories provide a baseline for understanding the effects of management and environmental changes on the biodiversity in a habitat as well as this biodiversity’s function (Hooper, Chapin et al. 2005). In an agroecosystem, bioinventories are especially useful to understand the relative abundances of economically relevant species (e.g., pests and their natural enemies) and how these interactions drive the profitability of the system

(Bredeson and Lundgren 2015).

Flies (Diptera) are one of the most harmful arthropod pest groups to cattle, affecting many aspects of livestock’s health; their bites irritate cattle and cause stress, weight loss, and transmit diseases that reduce ranch profitability (Campbell, Berry et al.

1987, Taylor, Moon et al. 2012) Two of the most economically important species, the stable fly, Stomoxys calcitrans (L.), and horn fly, Haematobia irritans (L.) (Diptera:

Muscidae), cost ranchers over $4.2 billion (in 2017 dollars) annually (Catangui, 103

Campbell et al. 1997, Byford, Craig et al. 1999). Filth flies like these lay eggs in dung pats where maggots consume dung and mature into adult flies (Pastor, Cickova et al.

2011), and thus management decisions that affect dung have important implications for fly management.

Under many rangeland systems, fly pests can grow to damaging levels quickly when cattle remain in a single pasture. To manage these fly pests, included along with all other arthropod and nematode pests of cattle, and reduce economic losses, ranchers apply pesticides to their animals, the most common of which are avermectins (Wolstenholme and Rogers 2005). There are other pesticides and antihelminthics used on cattle, however the ability of avermectin products to target internal and external parasites and pests of cattle have led to wide use of these products throughout the world (Omura and Crump

2004, Losey and Vaughn 2006). Avermectins are a synthetic endectocide that have a specific toxicity to arthropods and nematodes (Burg, Miller et al. 1978, Omura and

Crump 2004, Geary and Moreno 2012). This family of chemicals is used on over half of

U.S. cattle to reduce gastrointestinal nematodes, lice, mites, ticks, and flies (Campbell,

Fisher et al. 1983, Floate 2006). Avermectins are applied in a variety of ways (injections, topical sprays, slow-release bolus capsules, etc.), but their use can result in environmental problems (Madsen, Overgaard Nielsen et al. 1990, Strong 1992). Avermectins are often excreted in the dung of the treated animal; 80-90% of the active ingredient applied to the animal is found in the animal’s dung (Alvinerie, Sutra et al. 1998). Contaminated dung can reduce dung-dwelling pest species like maggots, but also adversely affects non-target dung arthropods, even at low levels (Wall and Strong 1987, Floate 1998, Verdu, Cortez et al. 2015). These non-target effects lead to a decrease in dung degradation rate, leaving 104 ranchers with a new set of problems such as pasture fouling and reduced nutrient cycling

(Wall and Strong 1987, Herd 1995, Strong, Wall et al. 1996). An alternative to chemical control of flies may lie in regenerative management of cattle herds.

Ranchers that practice a more frequent rotation program with high stocking rates can provide a more system with higher arthropod abundances that provides resistance to maggot proliferation through competition and predation (McDaniel, Boddicker et al.

1971, Valiela 1974, Skidmore 1991). Cattle dung is readily colonized by a diversity of insects (Finn and Giller 2000), most which are beneficial (Losey and Vaughan 2006,

Beynon, Mann et al. 2012). Dung pats are ephemeral resources, and competition from larger coprophagous insects like dung beetles can reduce food for maggots. Furthermore, tunneling and bioturbation of dung pats by competitors to maggots open the pat to predators that normally could not access the interior of the dung pat (Sanders and Dobson

1966, Chapter II). Coleopteran adults and larvae are potential predators that readily consume maggots (McDaniel, Boddicker et al. 1971, Wu, Duffy et al. 2011).

Management practices within the cattle operation can alter the dung arthropod community structure (Chapter III), thereby affecting pest management (Errouissi,

Alvinerie et al. 2001, Rombke, Coors et al. 2010).

In this study, the arthropod community was recorded on ranches representing a series of management systems, with specific attention paid to maggot abundance and the levels of beneficial species that would help suppress maggot abudnance. A systems level approach was used to see whether regenerative rangeland management practices influence the relationship between pest maggot species and their predators and competitors relative to more conventional rangeland systems. The effects of avermectin 105 use on maggot populations are described. An exclusion cage study accompanied these community observations to document maggot population growth in the absence of most competitors and predators. We hypothesize that management system will significantly alter the maggot community within deposited dung pats. We believe that regeneratively managed systems will be able to control maggot abundances with an increase in arthropod community structure rather than avermectin use.

2.0 Materials and Methods

2.1 Experimental design . Experimental ranches (n = 16; 10 in 2015 and six in

2016) represented a variety of cattle management practices in eastern South Dakota. The

16 cattle operations span 7,935 km 2 across eastern South Dakota. All sites were grazed by cattle for at least 5 y, but annual grazing intensity varied. Herds ranged from 20 to 120 individuals, and the cattle differed in size, breed, and the administered anthelmintics. The systems were ranked as regenerative, intermediate, and conventional based on several practices (Table 1). In our study, the most regenerative ranches do not use avermectins, and rotate high densities of animals frequently. Use of avermectin in the ranches was categorized as high (multiple applications during a year; scored as 0), low (single annual use, not applied during grazing period; scored as 1) and no avermectin (scored as 2). The stocking density (animal units [AU] per ha) was categorized as fewer than 5 animal units

(AU) per ha (scored as 0), 5-10 AU per ha (scored as 1), and more than 10 AU per ha

(scored as 2). Operations were categorized as having a rotation frequency of 30 d or more

(scored 0), between 10-30 d (scored as 1), and less than 10 d (scored as 2). Ranches with 106 the top 33% of scores were considered regenerative, the middle 33% of scores were intermediate, and the lowest third of scores were considered conventional.

2.2 Sampling procedure. Each of the ranches was sampled monthly from May to

September. Two- to 5-d old dung pats (n = 10 per ranch) were randomly selected from each ranch; this age of pat has peak arthropod abundance and diversity (Kessler and

Balsbaugh 1972, Lee and Wall 2006) (Chapter II). A core (10 cm diameter, 10 cm deep) was collected from each selected pat, and the arthropods within each pat was extracted using a Berlese system over 7 d, when dried cores had reached a constant weight.

Arthropods from each core were stored in 70% ethanol. All extracted arthropods were identified microscopically and cataloged; each unique specimen was identified to the lowest taxonomic level possible representing a functional morphospecies. Each morphospecies was placed into a trophic guild (coprophage, predator, parasitoid, herbivore, or pest) based upon previous descriptions of the biology of arthropod community in dung pats (Mohr 1943, McDaniel, Boddicker et al. 1971, Cervenka and

Moon 1991).

2.3 Avermectin ELISA . The amount of avermectin in dung pats was quantified using a direct, competitive enzyme-linked immunosorbent assay (ELISA) and following kit instructions (Product #5142B, Abraxis, Warminster, PA). A 500 μL (approximately

0.65 ± 0.02 g; mean ± SEM) sample was collected from five of the dung pats per field.

This sample was vortexed with 100 μL of water and 100 μL of ethanol for 1 min. The mixture was centrifuged at 14,000 g for 2 min and 50 μL of the resulting supernatant was analyzed. Absorbance values at 450 nm were recorded for each well on 96-well plates

(μQuant, Biotek Instruments, Winooski, VT). To quantify ivermectin in the dung 107 samples, a standard curve series with concentrations of 1, 0.5, 0.25, 0.1, 0.05, 0.025, and

0.01 ng avermectin/μL dung was included on each plate. Additionally, a negative control series of 0 ppm ivermectin was included in three wells on each plate. To distinguish positive samples from background absorbance of the matrix, the mean and standard deviation of the negative control series were calculated for each plate; any samples with a lower optical density (direct competitive ELISAs have an absorbance negatively associated with avermectin concentration) than the mean minus three times the standard deviation of this series were considered positive for avermectin.

2.4 Exclusion study. Previous work (Chapter II) revealed that maggots readily lay their eggs on the mesh of exclusion cages; we exploited this behavior to study how exclusion of arthropod communities affects maggot population growth. The experiment was conducted on a 130-ha mixed grass pasture at 44.75839, -96.538 in eastern South

Dakota, U.S., during the summer of 2016. The 130-steer herd that grazed on the pasture were excluded from the area where the experiment conducted. No insecticides had been used on the cattle for more than 10 y before this experiment.

Dung (<2 h old; 90 kg collected twice) was collected from the cattle before 10:00.

Fresh dung was homogenized and stored in bags at -25°C freezer for more than 72 h to kill any arthropods. Dung was thawed, reconstituted with distilled water to its original consistency, and measured into aliquots (1000 ± 10g) to form each experimental “sentinel pat” 24 h before placement into the field. Observation sites (n = 72) were placed 5 m apart in the pasture with each site consisting of a sentinel pat on top of a wire mesh (2.5 cm square holes) to allow for ease of pat removal. Dung pats were randomly assigned as to either an inclusion or exclusion treatment (n = 36 each). The inclusion pats were 108 entirely open and allowed all arthropods access to the dung. The exclusion pats were surrounded by a PVC cylinder (25 cm diam., 25 cm tall), buried >12 cm into the ground to limit colonization of the pat. The top of the exclusion cylinder was covered in a fine mesh screen (<1 mm opening) secured with a plastic tie. The experiment was repeated twice over the grazing season, once beginning on 10-June (early) and again on 28-July

(late).

Maggot and community composition was evaluated over time. Randomly selected pats (n = 6 inclusion and n = 6 exclusion) were removed at 2, 4, 7, 14, 28, and 42 d after the sentinel pats were placed. The pat was immediately sealed in a plastic bag, and was then dried in a Berlese funnel system to constant weight (over 7-10 d). Arthropods were collected via funnel system from the dung pat and arthropods were identified under microscope and weighed after 24 h drying to calculate arthropod abundance. The arthropod community was described similarly to methods listed above.

2.5 Data analysis. All statistics were conducted using Systat 13 and SigmaPlot 13 software (SYSTAT Software, Inc; Point Richmond, CA). ANOVAs were used to compare the effect that month and management system had on arthropod community metrics; abundance, species richness, diversity, and relative abundances of predators, coprophages, and pest maggots. Two-way ANOVA was used to determine the effects of treatment and time on the maggot and predator levels in the arthropod exclusion experiment in both early and late season.

3.0 Results

3.1 Description of dung arthropod community. Chapter III of this thesis includes a more detailed description of the arthropod community. A total of 800 core samples were 109 taken from dung pats over the 2-y study period. In sum, 116,244 arthropod specimens were identified representing 172 morphospecies. These species were represented by six classes of arthropods across 14 orders (Acarina, Araneae, Coleoptera, Collembola,

Diptera, Hemiptera, Hymenoptera, Isopoda, Julida, Lepidoptera, Lithobiomorpha,

Protura, Pseudoscorpiones, and Thysanoptera). Due to the difference in ecological function of larvae and adults, larvae were considered distinct morphospecies. Across all

16 ranches there was an average species richness of 34.76 ± 0.85 (mean ± SEM) species found site per month with an overall average diversity (Shannon H) of 2.07 ± 0.04. In total 18,501.02 ± 1,385.18 arthropods were found per m 2 of cattle dung throughout the study. Maggots represented 19,338 of the specimen collected and adult flies made up an additional 944 specimen.

3.2 Management system’s effect on maggots. Management system affected the complexity of the dung arthropod community (Chapter III), altering maggot abundance as a result. Dung in regenerative pastures had significantly fewer maggots than conventionally managed pastures (month: F4, 65 = 2.31, P = 0.06; management:

F2, 65 = 2.87, P = 0.047; interaction: F 8, 65 = 0.59, P = 0.79) (Fig. 1). Pastures with high stocking density, frequent rotation and no avermectin use had 1,990.32 ± 239.75 maggots per m 2; those pastures with an intermediate level of these practices had

3,457.33 ± 542.98, and those with low stocking density, infrequent/no rotation, and high avermectin use had 3,671.76 ± 689.19 maggots per m 2 dung. The quantity of avermectin in dung was significantly affected by the livestock management systems (F2, 77 = 46.34, P

< 0.001). The amount of avermectin found in dung was significantly and positively correlated to maggot abundance (F1, 78 = 6.01, P = 0.02). 110

3.3 Predator and competitor abundance and maggots. Management systems affected the ratios of maggots to beneficial groups of arthropods in dung. Management system had a significant effect on the ratio of maggots to predator arthropods per ranch

(F 2, 77 = 4.12, P = 0.02). The ratio of maggots to coprophagous arthropod abundance was similarly found to be significantly affected by pasture quality (F 2, 77 = 2.85, P = 0.04).

There were more maggots per predator and competitor on the ranches with low stocking density, low rotation frequency, and high avermectin use relative to the regenerative ranches (Fig. 2). Correlations between avermectin found in dung and both the maggot/coprophage (F 1, 78 = 7.16, P = 0.01) and maggot/predator (F 1, 78 = 3.78, P = 0.05) ratios were significant. In both cases, there were more maggots/predator and maggots/coprophage when avermectin levels were higher in dung pats.

Exclusion experiment. The abundance of early season predators was significantly different in the caged and uncaged pats, and their abundance changed as the dung pat aged (exclusion: F1, 60 = 32.27, P < 0.001; time: F 5, 60 = 7.66, P < 0.001; interaction: F5, 60 = 8.61, P < 0.001), with significantly more found in uncaged dung pats.

Predator abundance in the late season was similarly observed

(exclusion: F1, 60 = 4.44, P = 0.04; time: F5, 60 = 10.07, P < 0.001; interaction: F5, 60 = 2.56, P = 0.04), with a higher number of predators found in uncaged dung pats. Early in the season, the 7 d old dung pats contained higher predator numbers and later in the season 2-7 d old dung pats all had significantly higher abundances than other aged pats. Maggot abundance was also significantly affected by pat age and treatment in early (exclusion: F1, 60 = 47.35, P < 0.001; time: F5, 60 = 42.27, P < 0.001; interaction: F5, 60 = 22.20, P < 0.001) and late (exclusion: F1, 60 = 28.86, P < 0.001; 111

time: F5, 60 = 10.57, P < 0.001; interaction: F5, 60 = 11.84, P < 0.001) seasons (Figure 2).

Maggot abundance was significantly higher in caged dung pats and while uncaged pats remained statistically similar the 4 d and 7 d old caged dung pats had significantly highest abundances across all pats sampled.

4.0 Discussion

Conventional management practices such as frequent avermectin use and continuous grazing disrupted the pest management function of dung arthropod communities relative to that experienced on regenerative ranches. Adult pest flies can cause economic losses at very low densities, with three or more stable flies per animal leg reducing daily weight gain by 0.2 kg on grazing cattle (Campbell, Skoda et al. 2001). The multiple factors within a cattle operation, such as weather, diet, and cattle health, can make attempts to correlate pest fly abundances and reductions in weight gain challenging

(Campbell, Berry et al. 1987, Catangui, Campbell et al. 1997). Non-biting flies (house flies) may not disrupt cattle production at low numbers, but still may transmit harmful pathogens (Floate 2002, Gibson and Floate 2004). Predicting adult fly populations from maggot densities in the pats can be challenging. In a laboratory study, 74% of larval horn flies Haematobia irritans (L) survived to adulthood in manure (Perotti, Lysyk et al.

2001). While other fly species’ survival may be similar, environmental conditions and predators would likely reduce maggot survival and subsequent fly densities. Therefore, it can be assumed that the number of maggots that were found in the dung pat system would result in high abundances of adult flies. Management system affected maggot populations; ranches with frequent movement of high densities of cattle and 112 abandonment of avermectin use experienced the lowest maggot populations (Fig. 1 and

Fig. 2). We hypothesize that these results were the outcome of two influential processes: avermectin disrupted the balance of beneficial species in the conventional system, and a more diverse arthropod community in the regenerative systems consumed and competed with the maggots.

The amount of avermectin found in the dung was positively associated with maggot abundance in the pat. One explanation for this observed trend is that maggots may be resistant to avermectins. The high reproductive capacity of many dipteran species make developing resistance to an insecticide possible, such as the described widespread resistance to pyrethroid insecticides developed by H. irritans (Sheppard 1984, Sparks,

Quisenberry et al. 1985). Haematobia irritans develop complete resistance to ivermectin after 30 generations and other insecticides such as permethrin in only 21 generations

(Clark, Scott et al. 1994, Byford, Craig et al. 1999). An alternative explanation is that avermectin adversely affects the arthropod community that keeps maggot abundance in check. Avermectins have a broad spectrum of activity against arthropods, and through direct insecticidal activity (Strong 1992, Floate 2006) and repellent effects (Floate 1998,

Rombke, Coors et al. 2010) reduce the community structure within dung pats. This disruption of community structure results in a loss of ecosystem function, namely a reduction of dung degradation efficiency (Madsen, Overgaard Nielsen et al. 1990,

Dadour, Cook et al. 1999, Rombke, Coors et al. 2010). Dung pats that contained high levels of avermectins, such as ivermectin, are often avoided by coprophagous competitors to maggots such as dung beetles (Webb, Beaumont et al. 2010). Avermectins also adversely affect natural enemies of flies (Floate and Fox 1999). In our work, the number 113 of maggots per predator and per coprophage were exacerbated when avermectin was applied to the livestock. This could have reduced the biotic resistance to maggot proliferation. An alternative explanation is that ranches that abandoned avermectin use replaced this pesticide with high intensity flash grazing, which may have contributed to fewer maggots.

High intensity grazing systems foster higher levels of plant and microbial diversity (Stevenson and Dindal 1987, Stinner, Stinner et al. 1997) and may have contributed to a more diverse community resistant to maggot proliferation.

Implementation of regenerative practices, such as a frequent rotation regime, can increase overall biodiversity, improve soil quality, and result in greater nutrient sequestration (Earl and Jones 1996, Hodbod, Barreteau et al. 2016). Components of healthy arthropod communities that can help to reduce maggot abundance in dung include predators and coprophagous competitors. Two lines of evidence from our experiment support the hypothesis that dung arthropod communities are reducing maggot abundance in pats: ratios of beneficials to maggots in unaltered communities, and examining the rate of maggot population increase when beneficial species are reduced in the pat. Regenerative ranches had significantly more maggots per predator and coprophagous competitor relative to conventional ranches (Fig. 2). Predator communities can suppress the level of maggot pests found in dung pats (Valiela 1969, Valiela 1974, Sowig 1997). Along with flies, dung beetles and other hydrophilid coprophagous beetle species are some of the earliest colonizers to dung pats, flying to the freshly deposited dung pat (Errouissi, Haloti et al. 2004, Webb, Beaumont et al. 2010, Tixier, Lumaret et al. 2015). Competition 114 between maggots and large coprophagous species such as dung beetles can limit maggot populations by eliminating the dung resource (Fincher 1981).

Moreover, exclusion cages significantly lowered the abundance, species richness, and diversity of the dung arthropod community. The reduction of many predator and competitor species in the caged dung pats was associated with significantly greater maggot populations in both the early and late seasons (Fig. 3 and Fig. 4). We found only

26% of the maggot levels when they were raised on pats with a complete community of predators and coprophagous competitors. Indeed, predators and competitors were only

38% as abundant in the caged compared to uncaged pats. Evidence of competition from resource exploitation is supported by the fact that dung is removed 30 d more quickly when a complete arthropod community is allowed access to the pat (Chapter II).

Regenerative management practices in cattle operations result in a complex dung arthropod community structure capable of providing pest suppression services to the rancher. By adapting a multi-paddock rotation system and limiting or eliminating avermectin applications, a decision maker can create a pasture ecosystem where both cattle and arthropods mutually benefit from a symbiotic relationship.

5.0 Acknowledgements

Authors thank Michael Bredeson, Claire Bestul, Dakotah Grosz, Kae Januschka,

Nathan Koens, Marti La Vallie, Amy Lieferman, Abigail Martens, Alexander Nikolas,

Greta Schen, and Kassidy Weathers for their assistance in collecting, extracting, and sorting of insect specimen. Special thanks as well to Mark Longfellow in assisting with insect identification and all participating ranchers for their time and use of their pasture. 115

Ecdysis Foundation and NCR-SARE, via student research grant GNC15-207, funded this research.

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7.0 Tables

Table 1. The ranking of ranches (n = 16) on the regenerative quality of management practices. Management practices of cattle operations were scored 0-2 based on regenerative nature of the practice with higher number indicating a more positive regenerative practice. Avermectin application frequency was divided into multiple applications (0), single application not during grazing season (1), and no avermectin use

(2). Stocking density was divided into <5 AU/ha (0), 5-10 AU/ha (1), and >10 AU/ha (2).

Rotation frequency was divided into >30 d rotation (0), 10-30 d rotation (1), and <10 d rotation (2). Sum of these scores yielded a regenerative level for each operation Low = 0-

2, Medium = 3-4, and High = 5-6.

Avermectin Stocking Location Year Rotation Regenerative (frequency of density (closest town) surveyed frequency level applications) (AU/ha) Bruce, SD 2016 1 0 0 Low Castlewood, SD 2016 1 2 1 Medium Clear Lake, SD 2015 2 2 2 High Estelline, SD 2015 1 1 1 Medium Estelline, SD 2016 1 1 0 Low Flandreau, SD 2015 0 0 0 Low Gary, SD 2016 2 2 2 High Goodwin, SD 2016 1 2 2 High Madison, SD 2015 0 1 1 Low Milbank, SD 2015 1 1 1 Medium Milbank, SD 2015 0 0 0 Low Sioux Falls, SD 2015 2 2 2 High Summit, SD 2016 1 1 1 Medium Thomas, SD 2015 1 1 2 Medium Twin Brooks, SD 2015 2 2 1 High Volga, SD 2015 1 0 0 Low

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8.0 Figures

Fig. 1. Maggot abundance in cattle dung (mean ± SEM) over different management practices. Ranches (n = 16) were designated as regenerative, intermediate, and conventional based on stocking density, rotation frequency, and number of avermectin applications. Different letters indicate significantly different community characteristic among management systems (α = 0.05).

Fig. 2. The influence of management system on the ratio of pest maggots to other beneficial groups found in cattle dung pats. Maggot abundance in 2-5 d old dung pats were compared to the abundance of predators (A) and all non-maggot coprophages (B).

Ranches (n = 16) were designated as regenerative, intermediate, and conventional based on stocking density, rotation frequency, and number of avermectin applications. Different letters indicate significantly different community characteristic among management systems (α = 0.05).

Fig. 3. Exclusion cage study to determine how maggot abundance (mean ± SEM) in dung varies over time in the presence and absence of typical arthropod communities. Mesh cages excluded most of the arthropod communities from the developing maggots (n = 6 pats per treatment per age). Pats were examined twice during the growing season; beginning in June (A) and late July (B). Asterisks above bars indicate significantly different maggot abundances in the caged and uncaged pats for that specific sample age (α = 0.05).

Fig. 4. Exclusion cage study to determine how predator abundance (mean ± SEM) in dung varies over time in the presence and absence of typical arthropod communities. Mesh cages excluded most of the arthropod communities allowing fewer 125 species to enter dung (n = 6 pats per treatment per age). Pats were examined twice during the growing season; beginning in June (A) and late July (B). Asterisks above bars indicate significantly different predator abundances in the caged and uncaged pats for that specific sample age (α = 0.05).

126

Figure 1.

127

Figure 2. 128

Figure 3. 129

Figure 4.