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AL Greene

Dr. Greene is an entomologist and national IPM coordinator for the GSA’s Public Building Service in Washington, D.C. He can be reached via e-mail at


[A Look Back] The Rise and The Fall of the Action Threshold Concept

Market Watch

Action thresholds are dead. So why haven’t they been buried?

May 26, 2015

No other aspect of structural IPM doctrine so perfectly captures the essence of the discipline’s idealistic wing as does the commandment to establish action thresholds (ATs). Far more theatrics than science, this deeply rooted tenet of pest management orthodoxy is a Rorschach test of a practitioner’s background and objectives. Along with a few other anachronistic elements in the urban IPM playbook, once proposed as solutions for chemical risks that have long since been reduced to the vanishing point by more effective means, the idea that reactive control measures must be withheld until a pest population reaches a certain level of (numerically defined) disruption serves mainly to sabotage the credibility of the IPM paradigm for the audiences we most want to convince. It is the antithesis of the common-sense approach that IPM is supposed to embody.

Since we are talking about an armchair concept from the 1970s that has never been a widespread constituent of street-level IPM practice, why should we be concerned about it now? The answer lies in the maturation of pest control’s image from a unidimensional, janitorial trade distinguished by rote chemical application into an environmentally savvy discipline that is ideally practiced by experts with a multitude of integrated skills. Starting with the rise of the medieval guilds, increased professionalization always has been accompanied with an emphasis on formal credentialing as a means to ensure quality and exclude charlatans (as well as anybody else who doesn’t bow to the authority of the credentialing organization). Although I and many others see this trend as unfortunate when it comes to the validation of IPM practice, it is not going away and should be regarded as an inevitable toll of doing business in the 21st century.

In the world of public buildings (the sector that always has nurtured the vanguard of structural IPM), the premier custodian — indeed, the undisputed definer — of the green zeitgeist is the U.S. Green Building Council’s LEED (Leadership in Energy and Environmental Design) Rating Systems. And along with those other now-obsolete, procedural relics from structural IPM’s formative years (we’ll talk about those in future articles), the establishment of ATs by a building’s “IPM team” is a non-negotiable requirement to qualify for LEED’s Integrated Pest Management credit. Moreover, LEED gives a pass to facilities that hire contractors who are certified by one of the three IPM credentialing programs in the U.S., two of which also mandate the AT approach.

Since the mainstream of IPM practice manages to routinely prevent and control pests with a minimum of risk and without ever giving a thought to ATs, how did this curious state of affairs come to be?

Fields to Facilities.

The antecedents of ATs were integral to the first formulation of IPM principles for agriculture. Perhaps the most intellectually exciting and theoretically satisfying aspect of this revolutionary approach to controlling crop pests was its mathematical core. The two quantitative pillars of the strategy are the economic injury level (EIL) — the lowest population density of a pest that will cause economic damage — and the economic threshold, the point in time at which a control action should be initiated to prevent the EIL from being reached. As generally interpreted, the EIL is essentially a speculative concept that is extremely difficult to determine for any given cultivated field because of all the shifting variables contributing to that site-specific situation in that particular year. But not so for the economic threshold — regardless of its degree of accuracy in presaging an actual economic loss, it is a real-life moment, defined by a somewhat arbitrary pest population or crop damage level, when the control decision must be made.

Three historical aspects of this methodology are vital to analyzing its conceptual descendants. First and foremost, the process was always presented as a business plan for the owner of that crop. Second, “control” implied the expensive procedure of mechanized pesticide spraying that, in a conventional, non-IPM system, would be done by schedule and often with excessive, cost-inefficient frequency. Third, since those pesticides were broad-spectrum in effect, they inevitably had critical biological consequences beyond their immediate target. Thus, in addition to its role in maximizing a farmer’s profit, more incisive chemical use also conferred more expansive benefits in terms of increased environmental quality. It was this latter aspect of the early IPM paradigm that, of course, was — and still is — so alluring to such a broad range of citizens.

The first major diffusion of IPM thinking beyond crops was to ornamental plantings in urban landscapes. This was the grand entrance in the mid-1970s of the game-changing William Olkowski, who realized that the concept of pesticidal intervention as an efficiency-driven, situation-specific contingency to prevent significant pest damage could be seamlessly adapted to street tree canopies. Although spraying this sort of inventory certainly conferred an economic burden as well, the trees were simply being maintained for visual appeal rather than being grown for profit, thereby eliminating the need to reconcile cost against financial return. Taking advantage of the system’s diminished complexity — the goal was distilled down solely to minimizing insecticide use — Olkowski shifted the currency of decision making away from dollars to appearance. He termed the point in progressive canopy defoliation at which pesticides were necessary to avoid future damage that the average onlooker would perceive as unsightly to be the aesthetic injury level (AIL). Of even greater importance, Olkowski shifted the calculation of AILs away from a rigorous process of crunching vast pools of biological and economic data in elaborate models (which distinguished the prescription of EILs) to a subjective exercise involving nothing more complicated than public opinion surveys.

Olkowski’s conceptual leap was enormously influential beyond urban horticulture. It held out the possibility of a logical way to minimize chemical treatments for pests in buildings, the last frontier for the quickly spreading IPM ethos. Only a few years after the introduction of the AIL concept, Gary Piper and Gordon Frankie of Texas A&M University picked up the ball and ran with it in a fateful 1978 textbook chapter. Their discussion of the importance of public education in urban cockroach management programs began innocuously enough, focusing on the fatal flaw of classical (i.e., commodity-based) IPM when applied to the staples of fear and loathing: “The philosophy of integrated roach control is to manage populations at unobjectionable levels rather than to eradicate them. Obviously, this philosophy is incompatible with the public’s current preconception and expectation of pest control.”

But the revolution was young, and imbued with that central IPM vision of manipulation based on mathematics, they next threw down a provocative gauntlet that was to reverberate for decades: “Determination of realistic levels of tolerability or aesthetic injury levels, A.I.L., (i.e., levels of insect abundance or damage which offend the aesthetic values of people)...are important to the development of an effective cockroach management system. Human attitude toward these domiciliary insects ranges from indifference to intolerance, but in most instances only very low numbers (zero to five cockroaches observed per week) inside a residence are acceptable.”

Since the presence of even a single cockroach has always been clearly unacceptable to those who actually pay the bill for pest control service in most venues, the expression “zero to five” became an inflammatory symbol to the industry rank and file watching from the trenches. Even leaders in the trade who were generally sympathetic to the new IPM paradigm did not hide their scorn that control actions could possibly be governed by the on/off switch of any sort of rigidly prescribed number that (in stark contrast to an economic threshold) had basically been pulled out of a hat. I was present at a particularly sardonic conversation among several influential pest control company owners that uncharitably speculated whether Piper or Frankie would tolerate the observation of five cockroaches per week in their own offices, much less their homes.

From Academia to Activism.

Despite the strong whiff of absurdity, quite a few members of the newly developing urban IPM community in academia and government were still willing to give the concept a try. Their efforts were often dismissed by those in the industry as the idle abstractions of dreamers whose paychecks did not depend on direct customer reaction. In reality, their motives were no different than those of Olkowski — it was the standard industry operating procedure of excessive surface/space spraying by schedule (with the common organophosphate and carbamate products of the era) that provided even the most down-to-earth reformers with all the incentive they needed to search for a compelling, mechanistic alternative that could provide the basis for a more restrained approach.

In a 1984 article that served to define the challenge, Pat Zungoli and William Robinson of Virginia Tech noted that most residents in public housing projects perceived cockroaches as a serious problem and had minimal tolerance for even low numbers in their living space. They also predicted that tolerances would diminish even further as control success increased (a fundamental concept discussed by structural IPM prophet Hugo Hartnack in the 1940s), thus leading to a progressively diminished acceptability of programs that aimed for suppression rather than total elimination. Acknowledging that “The level of control must reflect the attitudes of the target audience,” they emphasized that acceptance of the AIL concept was dependent on resident education programs to sell the idea.

All in all, it was not a particularly strong endorsement. Interestingly enough, this paper also marked the general demise of the term “aesthetic injury level” among structural entomologists — within a few years, it had been almost completely replaced with the stronger, more operationally oriented “action threshold.” And although there were a few additional attempts by academic researchers to get a handle on the issue, by the mid-1990s, the concept had largely been abandoned. A status review written by Robinson and Brian Forschler of the University of Georgia in 1999 is equally valid today. Their discussion focused on ants and termites, but applies to the total structural pest assemblage:

“There are…no established action thresholds for insect pests, including ants or termites, in the urban environment…It is our opinion that there are two major reasons why research-based action thresholds have not been established for urban ant and termite pest species. First, research designed specifically to provide background information for action threshold establishment has not been conducted, or the available scientific literature has not been collated to provide both the monitoring program and measure(s) of population indices needed. Second, monitoring an insect pest population is labor-intensive and time consuming. As a result, most practitioners and consumers are not willing to underwrite the maintenance of a monitoring program because of the inherent cost involved.”

With the industry firmly united in opposition for pragmatic reasons, and many in the urban entomological community preferring that ATs be objectively based (while acknowledging that the necessary data simply didn’t exist), there remained only one stakeholder group who continued to be strongly receptive to the concept — the environmental and social activists who promoted IPM almost exclusively as a pesticide reduction issue, and who, by the early 1990s, were increasingly focusing their efforts on schools. Ironically, for much of the decade, these reformers advocated ATs as an essential IPM component far more often than they actually specified them in real-life circumstances.

But supporters were emboldened in 2000 by the publication of a remarkable document commissioned by the Maryland Department of Agriculture, funded by an EPA grant, and written by the venerable pest management consulting team of Larry Pinto and Sandra Kraft. Entitled “Action Thresholds in School IPM Programs,” the eight-page pamphlet boldly strode in where others had feared to tread, proposing concrete examples of ATs for 23 pest categories, from ants to yellowjackets. As one of the most ambitious attempts to bring this type of quantification to life, the guidance has since been reproduced by countless other sources of information on school IPM. The section on cockroaches offers the following values:

  • Classrooms and other public areas: TWO cockroaches/room.
  • Infirmary: ONE cockroach/room.
  • Kitchen: ONE cockroach/room
  • Maintenance areas: FIVE cockroaches/room.

No mention was made of the rationale behind these numbers, but that wasn’t the point. Pinto and Kraft made a valiant effort at what they had been hired to do by one of the most ideologically strict school IPM programs in the country. In so doing, by having the intellectual honesty to take the AT concept to its logical conclusion, they created an almost satirical instruction — the perfect argument for dispensing with the notion entirely (Figure 1).

Five Reasons for Rationality.

In summary, the inclusion of ATs in structural pest management doctrine was probably an inevitable phase in the journey to make the biorational aspects of agricultural IPM relevant for the built environment. Unfortunately, the original paradigm was based on economic principles designed to meet the business needs of farmers — in retrospect, not a robust choice for an acid test of IPM legitimacy in structural venues. Today, this legitimacy derives from an emphasis on prevention, an analytical, systems approach to problem solving, and a restrained use of pesticides (with no sprayed formulations of any type unless absolutely necessary), rather than a Procrustean, numerical aspect to decision-making.

Here are the top five reasons why ATs should be allowed to fade away for good:

1) They’re arbitrary and inflexible (at any given moment). Pest challenges in buildings often involve numerous, complex variables that cannot be readily distilled into precise laws. A responsive process based on a highly subjective, prescribed quantity is the exact opposite of the site-tailored philosophy that IPM represents.

2) They’re ignored by the customers. ATs are the Prohibition of structural IPM. Not only do they subject the program to ridicule as concealed cans of illicit bug spray proliferate behind the backs of the earnest IPM missionaries, they put the technician on the front line into an untenable position with the building occupants.

3) They emphasize superficial data collection rather than synthetic problem solving. Since one of the primary objectives of an IPM program is to employ specialists who are capable of skill-based, qualitative decision-making rather than blindly following a numerical cookbook, an unavoidable interpretation of ATs is that they are an admission of failure in hiring, training or writing contract specifications.

4) They’re already set at one or very close to one for most pests in most programs that use them. Since “prophylactic” chemical treatments in the absence of pests are already banned in even the most rudimentary IPM programs, one might legitimately ask how an AT of one functionally differs from no AT whatsoever.

5) They’re now superfluous for decreasing pesticide use and risk. Back when indoor treatments were synonymous with monthly hosing of pest-free baseboards, ATs may have made sense as simply another way of stating that this would not be tolerated. But the world has changed and IPM has matured. Minimization of risk nowadays is “built in” with universal rules of engagement that emphasize baits, traps and other non-chemical approaches where scheduled surface and volumetric spraying used to rule (Figure 2). Essentially, IPM has made action thresholds obsolete.


The author gratefully acknowledges Larry Pinto and Sandra Kraft for their review of this manuscript, which has been adapted from a forthcoming book on the theory, history and practice of IPM in buildings. The opinions expressed herein are the views of the author and do not necessarily reflect the official policy or position of the U. S. General Services Administration (GSA). Dr. Greene is entomologist and national IPM coordinator for the GSA’s Public Building Service in Washington, D.C. He can be reached via e-mail at agreene@

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