Contributions of Dung Arthropods to Sustainable Pest Management in Rangeland Systems of the Northern Great Plains

View the project final report

Commodities

• Animals: bovine

Practices

• Pest Management: contributions of dung arthropods

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 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.

Introduction:

Accumulated cattle dung reduces ranch profitability by suppressing plant growth, polluting pastures and providing a habitat for pests and parasites of cattle. When a dung pat is deposited on a pasture, all of the available forage around the pat is unused by grazing cattle until the pat is broken apart and incorporated into the soil. A large number of dung arthropods inhabit cattle dung and provide a crucial role in breaking apart dung and increasing the nutrient cycling in rangelands. While a majority of arthropods are beneficial, there are pest species found within the community.  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 transmitting diseases that reduce ranch profitability. Filth flies lay eggs in dung pats where maggots consume dung and mature into adult flies, and thus management decisions that affect dung have important implications for fly management. To manage these pests and reduce economic losses, ranchers apply pesticides to their animals, the most common of which are avermectins. Avermectins are applied in a variety of ways (injections, topical sprays, slow-release bolus capsules, etc.), but their use can result in environmental problems. Avermectins are often excreted in the dung of the treated animal; 80-90% of the active ingredient applied to the animals is found in the animal’s dung. Non-target effects lead to a decrease in dung degradation rate, leaving ranchers with a new set of problems of pasture fouling and reduced nutrient cycling. 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 biologically diverse system that provides resistance to maggot proliferation through competition and predation.

The present report summarizes several studies that observed the dung arthropod community structure, quantified benefits to arthropods presence in cattle dung, and how management practices will affect the community in eastern South Dakota pastures.

Study 1 uses an exclusion/inclusion cage system to evaluate the role of dung arthropods on dung degradation over time in eastern South Dakota. Exclusion cages help to isolate the arthropod community’s contribution to dung pat degradation. 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.  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.

Study 2 observes the effect of the combination stocking density, rotation frequency and endectocide use on arthropod community. This experiment will observe how the management practices typically used in eastern South Dakota will alter the dung arthropod community. If ranchers in the area are choosing more regenerative management practices, then there could be a correlation to a more complete dung arthropod community structure. 

Study 3 will finally use the earlier mentioned arthropod community on ranches representing a series of management systems, with specific attention paid to maggot populations. 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 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. The results demonstrate that ecologically intensive management systems for cattle offer superior maggot suppression relative to systems reliant on avermectins.