Pest Susceptibility Commons in Agriculture

By David A. Hennessy and Yanan Jia

Pest resistance to control technologies are causing costly management problems in crop and animal agriculture. Pest resistance often arises from heavy use of a particular control technology, a choice that makes sense to each individual farmer but may leave all farmers worse off. Viewing pest susceptibility to control as a commons, or common good, admits an understanding of policy responses intended to protect against excessive use of pest control technology. Common goods are characterized by two criteria—the good is rivalrous so that use by one person takes from use by another; and, it is also non-excludable so that those who do not pay can use the good. Excessive use for the social good, a reduction in resource availability, and a decline in resource quality generally ensue. Better management of the good requires mechanisms to both limit consumption and direct goods to those who v­­alue them most. These possibilities are not available for non-excludable goods. The extent to which either definition criterion is met varies greatly; and yet there is consensus that the underlying concept captures the essence of many resource use problems. We discuss some classical agricultural common good (ACG) issues as well as topical examples with emphasis on pest susceptibility to applied chemicals.

Historical examples

The classic commons problem, livestock on commonage grazing, is remarkably clear in illustrating the criteria, some limitations, and also the robustness of the underlying concept. Grass is a rivalrous good while common grazing ground is non-excludable in that many owners can place stock upon the land. Exclusion may be unprofitable absent any other consideration and may also be difficult due to property laws and the social mores or politics underlying these laws. 

Soil erosion, and in particular the US Great Plains Dust Bowl event of the 1930s, illustrates a more involved ACG problem. For land under drought and inappropriate management, strong wind will blow small soil particles far away and larger particles nearby. The originating land declines in subsequent productivity but the farmer may accept future yield losses when practices causing the losses, primarily continuous cropping and intensive cultivation, enhance the near-term profits that small farm operators needed in the 1930s. The problem is one of displaced soil as much as lost soil. Large particle soil is, once settled on neighboring land, unproductive. Rivalry here regards near-term profit on one’s own land at the expense of profit on nearby land. Non-excludability is more subtle. The ‘good’ is now a bad. Rather than preventing entry without payment, the challenge is to prevent other farmers from taking actions that cause the bad to exit and rest at the wind’s whim. Policy remedies at the time included compulsory fallowing as well as mandated and incentivized changes in land management practices. Hansen and Libecap (2004) argue that the presence of larger farms was the most effective solution then and later. Large farm operators were generally not in dire need of cash, and also, being their own neighbors, internalized much of the externality.

Pest susceptibility commons

We explain the perspective that a pest’s susceptibility to a treatment is rival, is non-excludable, and declines over time with reference to three examples—weeds, insects, and microbes.

Weeds: Inclusion of herbicide resistance traits into soybean, corn, cotton, and some other crops since about 1996 has created a weed susceptibility commons (SC). At the price of the trait premium, farmers can spray over their crop with an all-purpose herbicide, killing weeds but not their crop. When the seed is commercially available without restriction, only price limits exclusion from using the SC. Rivalry arises because, through genetic selection, each weed species eventually becomes resistant to herbicide exposure. This cost for individual use is deferred and can be at least partly incident on other farmers. Management can involve enforcing non-market approaches to exclusion from using the technology. However for herbicide-resistant crop such use restrictions have generally not been imposed. A prevailing belief is that the cost of weed resistance is mostly internalized into farmers’ private decisions because weeds and seeds generally have low mobility, and so policy intervention is likely ineffective for the weed SC. Whether this logic is valid is unclear, but weed resistance to glyphosate is now widespread in the United States (Landau et al. 2023). 

Insects: Plant-incorporated pesticides (PIPs) are insect toxins built into the seed and thus expressed throughout the plant material. These toxins are proteins synthesized from the Bacillus thuringiensis (Bt) bacterium where different proteins have proven effective against different insects. There is an insect SC—when producers use toxins in excess then resistance will come to dominate susceptibility in the insect’s gene pool. Rivalry is again with others who seek to use the SC and also with one’s future self. In this case, however, the mix decidedly tilts toward rivalry with others because winged-phase insects are far more mobile than weeds. 

Figure 1 adapts the standard schematic for characterizing a common good. The vertical dimension represents degree of exclusion with 0 at top and 1 at bottom. Rather than placing a rivalry index, as is standard, on the other axis we focus more generally on the externality effect. The standard common good problem focuses on a private benefit that people can access for free. Leaving aside the trait price, the insect SC problem is that the damage done is diffuse and extends beyond someone else’s animal not having the opportunity to consume the grass. We focus on all external effects and not just removing someone else’s opportunity to consume a specific good. Here 0 is at left and 1 is rightmost on the horizontal axis. A common good is in the upper right corner and the desirable location is across the box diagonal, a private good that does not cause commonly shared damage. Management approaches can seek to exclude through technology use restrictions, to reduce the magnitude of external spillover or do both.

Figure 1. PIP policies to alter excludability and external damage attributes in the insect susceptibility commons.
Figure 1. PIP policies to alter excludability and external damage attributes in the insect susceptibility commons.

The US Environmental Protection Agency saw early the need to intervene through a means of exclusion, the refuge requirement whereby farmers had to sow a specific fraction of a crop with toxin-omitted seed. PIP with refuge relocates the PIP seed in the figure further along the exclusion axis to render it more like a private good, albeit one that can cause commonly shared damage. An alternative approach is referred to as ‘pyramiding’ whereby multiple distinct PIP toxins are bundled in each seed so that the insect faces multiple distinct barriers to adaptation. This approach seeks to reduce the external effect by reducing the rate at which susceptibility declines. A third approach, although similar to pyramiding, is to incorporate one toxin at a high dose rate so that even mildly susceptible insects will die so that their genes disappear from the gene pool. Again, this approach amounts to reducing the external effect. We characterize both of these alternatives as shifting the good’s location leftward and so again closer to the desirable lower left corner.

Figure 2 shows a timeline of documented Bt resistance development for different toxins in commercial corn. If there is a trend then time from first commercialization of a Bt toxin to first documented field-evolved resistance to the toxin declined over time. Cross-resistance mechanisms, in which species resistance to one toxin facilitates resistance to other Bt toxins, may have contributed to more rapid field-evolved resistance (Tabashnik and Carrière 2017), showing the importance of early and deliberated management.

Figure 2. Bt resistance development in Bt corn in the United States.
Figure 2. Bt resistance development in Bt corn in the United States.
Notes: 1. Each bar indicates when the corresponding Bt toxin was first commercialized and when field-evolve resistance was first documented. Data were extracted from Yang et al. (2013) and Tabashnik and Carrière (2017). 
2. Cross resistance is suspected or known to contribute to Cry1A.105 x Cry2Ab2, mCry3A, eCry3.1Ab toxin resistance (Tabashnik and Carrière 2017). Field-evolved resistance to eCry3.1Ab was documented in the year it was first commercialized.

Microbes: Most antibiotics consumed in the United States are by non-human species, mainly animals for food. For many antibiotics, microbe susceptibility has declined over time. A distinction relative to the weed and PIP SC is that the social welfare goal in resource management extends beyond the agricultural and food sectors. Resistant bacteria genetics originating from other species may make their way to those that harm humans, resulting in many human fatalities. In the United States, recent policies to manage antibiotics include the Veterinary Feed Directive (VFD), with implementation by the Food and Drug Administration completed in 2017, and Prescription Regulation (PR), implemented in 2023. VFD places veterinarians as the authority on whether antibiotic administration through feed or water are appropriate in a specific setting. PR requires that medical professionals prescribe all antibiotic uses. VFD and PR are intended to enforce exclusion through non-market means. Figure 3 presents recent US-level antibiotic use trends in food-producing animals. The long-run upward trend was reversed in 2016. Between 2015 and 2017, use of medically important antibiotics in agriculture declined by 43% and accounted for most of the 30% overall decline in antibiotic usage in agriculture. While likely a prudent and overdue policy stance, a formal economic analysis of costs and benefits would be challenging because the underlying biology of resistance-trait transfer is poorly understood.

Figure 3. Antibiotic sold or distributed for use in food-producing animals.
Figure 3. Antibiotic sold or distributed for use in food-producing animals.
Data source: US FDA (2023).


If producers can deplete a pest management tool’s susceptibility status with confidence that an acceptable alternative will emerge then its obsolescence should be of little concern. Both pesticides and antibiotics markets witnessed a long hiatus in product development during recent decades. Consistent with the induced innovation hypothesis, however, the past decade saw commercial developments to address the decline in effectiveness of older pesticide (Umetsu and Shirai 2020) and antibiotic (Chin et al. 2023) products. We might count ourselves fortunate because SC has an unique, pernicious feature—need for a product when combined with sound management of the existing resource may not translate into profit for an innovator whose product encompasses the SC property (Årdal et al. 2020). Consumers should rarely use new products in order to protect against the emergence of resistance, so that the revenue stream to compensate for a likely expensive and risky investment may not suffice to induce innovation. 

The essence of the SC problem is physical and biological openness. Sharing air, water, infrastructure, genetic, and other resources can reduce production costs, increase product benefits, and facilitate trade gains. But there are also costs, one being the erosion of susceptibility. The crucial question is how to manage the rate of erosion. This is a hard question as the response depends on technological details, including genetic trait attributes as well as the prospects for finding a commercially viable replacement. Institutions, as with property and patent law details, and quality of research infrastructure matter. So too do social preferences, as with balancing gains and losses across sectors, valuing animal welfare, and addressing the ethics of gene drives. Furthermore, the economic and intellectual climates are relevant. A dynamic society may at once be more exposed to decline in pest susceptibility and better prepared to find replacements for an eroded resource. 


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Suggested citation

Hennessy, D.A., Y. Jia. 2024. “Pest Susceptibility Commons in Agriculture.” Agricultural Policy Review, Winter 2024. Center for Agricultural and Rural Development, Iowa State University. Available at: