Kicking up a stink. The economics of agriculture

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The impact of the brown stink bug (Euschistus servus) on the financial success of America’s crops is not to be taken lightly. Research by Dawn Olson of the United States Department of Agriculture Agricultural Research Service aims to understand more about the breeding habits and life cycles of this pest species. The financial implications of managing the species are wide-ranging, but by using predatory species to reduce pesticide use to control infestations Dawn Olson and her team ensure that the environment will be protected alongside the economy.

Adult brown stink bug, Euchistus servus.

Farmers all over the world suffer economic damage to their crops infested by stink bug pests. In North America, three stink bug species, in particular, are capable of damage to a number of crops that without control can substantially reduce farmers’ profits. Researchers from the United States Department of Agriculture- Agricultural Research Service, the University of Georgia and the University of Minnesota conducted a large scale study in the south-eastern United States into the ecology of the brown stink bug (Euchistus servus) a native and currently dominant stink bug species in much of the region. The information collected during this research allows scientists and farmers to develop more environmentally and economically friendly methods of controlling this destructive pest.

Solenopsis invicta. Photo Credit: CC BY-SA 4.0

A plague of bugs
With its piercing-sucking mouthparts, the brown stink bug is capable of causing severe damage to the fruiting structures of crops. The piercing wound itself is a portal for pathogens, thereby further damaging the fruit and reducing yields. The creature, which measures approximately 1.5cm when fully grown, is a selective forager and can travel as far as a kilometre every day to choose its food. Due to their ability to produce two generations each year with each female producing on average 500 eggs per generation, it is easy to understand how their population could spiral out of control if left untreated.

The financial implication of a spiralling pest population has the potential to devastate livelihoods. The scale of destruction leaves farmers desperate to protect their crops and eliminate the brown stink bug. At present, populations are primarily controlled using synthetic insecticides which have negative impacts on the biodiversity of the area they are used in. Research continues into the long-term consequences of using insecticides, but many ecosystem services are threatened by their use. Potential problems include freshwater pollution, soil quality deterioration and accidental damage to pollinator and natural enemies of pest populations.

The effect of the brown stink bug on crops has been analysed to cost farmers in the range of $10-$75 per acre. These costs arise from two sources. Initially, costs are incurred when crops are damaged by the bugs. Crops plagued by bugs are no longer able to be sold and the profit margin of their land narrows. Secondly, farmers must bear the financial burden of pest management. Farmers of certain crops, such as soybean, may find themselves disproportionately bearing the brunt of pest management costs due to the brown stink bugs predisposition to reproduce at a higher rate in their preferred crops.

Geocoris punctipes. Photo Credit: CC BY-SA 4.0

The effect of the brown stink bug on crops has been analysed to cost farmers in the range of $10-$75 per acre.

Fortunately, the brown stink bug has natural egg predators that can control the population by destroying young stink bugs before they hatch. One of the aims of this research was to better understand the predator-prey relationship between the brown stink bug and two of their key predators- red imported fire ants (Solenopsis invicta) and big-eyed bugs (Geocoris spp.). The researchers intend that a better understanding of biological methods of pest control could minimise the need for chemical control.

Studying the stink bug
This latest research by Dawn Olson and her team built on their previous work which identified that current crop rotation practices in the USA can contribute to increased stink bug populations on certain crops. Major crops such as peanut, maize, soybean and cotton are often grown in rotation or in close geographical proximity. Previous research has shown that the stink bug prefers soybean crops. Therefore, when soybeans are grown other crops nearby are less likely to suffer brown stink bug infestation unless their infestation is so high as to spill-over into acceptable but less preferred nearby crops. The team have also conducted studies which aim to improve their understanding of the natural mortality rates of the brown stink bug.

One landscape illustrating sampled fields and crop types in southern Georgia.

Their latest project was a large-scale study based in Georgia, North America. This work sought to go further than identifying stink bug habits or qualities and sought to understand more about two of their key predator’s behaviour as well. In order to do this the reproductive rate of the brown stink bug and the density of their predators’ populations were measured. The four major crops of maize, peanut, cotton and soybean were the crops used in this research. The project encompassed data collected in 192 fields during the three-year study period.

Estimation of relative finite rate of population increase (λ generation-1).

Throughout the project, researchers applied multi-disciplinary knowledge and skill to carry out the project as they combined their entomological knowledge with their understanding of the pressures of agriculture as an industry. The effective use of interconnected knowledge and skills from a highly skilled team, led by Dawn Olson- herself an experienced mentor, allows for the best application of results in a real-world context.

This research provides support for biological pest control over chemical pest control.

Cotton field. Photo Credit: CC BY-SA 4.0.

The team found that the type of crop being grown was the single most important variable in the measurement of brown stink bug reproduction rate. Reinforcing their earlier work which identified a preference for soybean crops, this study also found reproductive rates increased as the amount of soybean crop increased. They found the lowest reproductive rate in cotton crops which they believe is due to the higher rate of insecticide application on cotton crops compared to the other crops studied.

Of the two key predators to feature in this research, the big-eyed bug was most likely to be found in the brown stink bugs preferred soybean habitat. They could also be found in maize whereas fire ants were dominant in peanut and cotton crops. Researchers found no interaction between the predator species and concluded that their presence being distributed across different crop types contributed to lower rates of reproduction for the brown stink bug. Though these predators possess largely complementary characteristics, the team did identify one key difference between their prevalence. Fire ants were more prevalent in areas which featured woodland whereas big-eyed bugs were less common in these areas.

Soybean field. Photo Credit: CC BY-SA 3.0

Environmental and economical interventions
Findings such as these are important stepping stones towards offering farmers conclusive advice about the best strategy for ecological pest management. These results produce several important environmentally and financially beneficial opportunities for farmers to better control pest species. Firstly, this research provides support for biological pest control over chemical pest control. Any strategy which reduces the need for introducing further potentially harmful chemicals to the natural world is an important contribution to protecting native biodiversity. A second important factor is that researchers studied the potential of native and naturalised- species as pest control agents, not introduced species. This reduces the potential impact of introducing a hostile non-native species. As well as fire ants and big-eyed bugs the researchers also identified six other stink bug predators which as a whole, were found capable of significantly reducing the reproductive rate of this pest. Finally, the financial benefit of reduced crop wastage and more efficient land use promotes a more sustainable model of pest control for farmers to aspire to.

Peanut field. Photo Credit: CC BY-SA 3.0

As social conscience increasingly becomes attuned to the devastating impact human actions can have on the natural world, research into biological alternatives to chemical pesticides becomes increasingly important. Alongside environmental awareness, our planet is facing an ever-growing human population which will require sustainable food sources for the future. Any research which can minimise waste and maximise productivity, without harming the environment, should be welcomed by all. Large-scale studies of this nature should inspire future research into alternative methods of pest control to ensure that efficient food production can continue for generations to come.

What was your biggest motivation for undertaking this research- the environmental or the economic aspects?

I think of these processes as interchangeable. While we do not typically place a monetary value on environmental processes, they can be substantial through, for example, water quality and overall natural resource preservation which are crucial to the long-term sustainability and resilience of agro-ecosystems. On the other hand, sufficient economic returns are crucial to growers to ensure their livelihood and ability to produce commodities for a growing population.

References

Chagnon, M., Kreutzweiser, D., Mitchell, E.A., Morrissey, C.A., Noome, D.A. and Van der Sluijs, J.P., (2015). ‘Risks of large-scale use of systemic insecticides to ecosystem functioning and services’. Environmental Science and Pollution Research, 22(1), pp.119-134.
Landis, D. A., (2016). ‘Designing agricultural landscapes for biodiversity-based ecosystem services’. Basic and Applied Ecology, 18, pp.1-12.
Olson, D.M., Prescott, K.K., Zeilinger, A.R., Hou, S., Coffin, A.W., Smith, C.M., Ruberson, J.R. and Andow, D.A., (2018). ‘Landscape Effects on Reproduction of Euschistus servus (Hemiptera: Pentatomidae), a Mobile, Polyphagous, Multivoltine Arthropod Herbivore’. Environmental Entomology, 47(3), pp.660-668.
Olson, D.M., Zeilinger, A.R., Prescott, K.K., Coffin, A.W., Ruberson, J.R. and Andow, D.A., (2018). ’Landscape Effects on Solenopsis invicta (Hymenoptera:Formicidae) and Geocoris spp. (Hemiptera: Geocoridae), Two Important Omnivorous Arthropod Taxa in Field Crops. Environmental Entomology, doi: 10.1093/ee/nvy104.
Olson, D.M., Ruberson, J.R. and Andow, D.A., (2016). ‘Relative longevity of adult Nezara viridula in field cages of cotton, peanut, and soybean’. Entomologia Experimentalis et Applicata, 159(1), pp.30-36.
Olson, D.M., Ruberson, J.R., Zeilinger, A.R. and Andow, D.A., (2011). ‘Colonization preference of Euschistus servus and Nezara viridula in transgenic cotton varieties, peanut, and soybean’. Entomologia Experimentalis et Applicata, 139(2), pp.161-169.

Research Objectives
Dr Olson is conducting research that increases our understanding of multi-trophic interactions and insect behaviour in major crops of the region, so we may develop alternatives to the chemical management of insect pests.

Funding
NIFA National Institute of Food and Agriculture

Collaborators

David Andow
John Ruberson
Adam Zeilinger
Alisa Coffin

Bio
Dawn Olson has been a Research Entomologist with USDA-ARS since 1998, directing and conducting research on insect behaviour and population ecology that contributes to crop protection using methods that both increase crop production and minimise negative environmental impact. She is an international collaborator, and a mentor of several graduate students and interns.