Resistance Management Reviews

Principles of Insecticide Resistance Management

Progress Review of the 5-Year National Research and Action Plan for Development of Management and Control Methodology for Sweetpotato Whitefly

T.A. Miller
Entomology Department
University of California
Riverside, CA 92521
United States

I thank Nick Toscano and Tom Henneberry for the invitation to this meeting. I was asked to say something about resistance management in a few minutes. Of course, such a task is impossible. Instead, I would like to share some facts with you that, it seems to me, are important to remember when considering problems like the whitefly and resistance.

Agriculture and Capitalism
All segments of society that are involved in food and fiber production are driven by a profit motive. This is illustrated by what I call the greed chart (Table 1).

Although it is clear that Agrochemical industry is in business to make money, growers are too. This fact should be kept in mind when considering resistance management.

Another fact not appreciated enough is that Universities, including Agricultural Experiment Stations are in the business of raising money. By slow attrition, State funds now account for about 1/4 of University budgets. The rest comes from the indirect costs of grants and other sources.

Resistance Management
Resistance management is relatively simple to do because there are few choices. Despite all the groups listed on the greed chart, there are two and only two players in the resistance game - growers and insects. All other entities play an indirect role at most.

Although there are some very important exceptions, we know intuitively that if a grower uses a given insecticide on a regular basis, resistance to that compound will eventually occur. We also know that if this hypothetical insecticide is used more frequently, we can expect the resistance to occur sooner rather than later. Guessing how soon is the part of the game that the growers get to play. Everyone else watches, therefore:

Resistance Management is a Guessing Game
We know the simple Mendelian explanation for how resistance is inherited; however despite this being the age of molecular genetics, we really don't know any details about how resistance occurs in the first place.

Genes are required to confer resistance. Where do these genes come from? Were they there all along? In most cases yes, but in a few cases probably not. Genes can be activated in insects to produce metabolic enzymes in response to dietary plant toxins, probably one of the original selection mechanisms in evolution, therefore:

Resistance Management is a Genetic Phenomenon
One thing is clear from a close look at the resistance game. The large populations and high turnover rate of insects give them a distinct advantage in overcoming insecticide treatments. In addition, the phenotype of resistance is difficult to measure especially in a single individual, therefore one usually resorts to measuring populations. The more insects we use to measure resistance, the better and more reliable are the measurements, therefore:

Resistance Management is a Numbers Game
The field of health is like the practice of farming in a way. Instead of keeping plants healthy, medical doctors keep people healthy. The analogy comes close to home when confronting the problems of resistance to antibiotics.

How does the health field handle resistance? An extensive resistance management program is an integral part of every good hospital. Pests (bacteria in this case) are collected from the patient, grown in lab culture and identified. In the same lab cultures, the antibiotics that discourage growth are also identified before the medicine is ever prescribed. This can all be done in a few hours.

Anyone struck with a chronic infection that shows resistance to all antibiotics would be faced with a potentially serious situation (not unlike the present inability to control certain whiteflies in agriculture) were it not for a uniformly strong effort put into finding new antibiotics.

Naturally, the newest and most potent antibiotics are not used unless absolutely necessary because hospitals practice resistance management (and incidentally because these newer products happen to be very expensive - the greed factor at work).

Resistance Management as Practiced in a Hospital
Medicines are discovered the same way pesticides are discovered. After all, pesticides are just another antibiotic. Indeed, many of the companies in the business of finding pesticides are also in the business of finding pharmaceuticals such as DuPont, Merck, Sandoz, etc.

Our colleagues in the medical profession have several advantages over us in agriculture. In addition to their salaries being higher, they have access to far more research funding. Indeed, we as a nation are spending a lot more money keeping people alive than we are on feeding them. The costs of modern medical technology continue to climb while food remains stagnant by design, therefore:

Insecticide Resistance Research is Underfunded
It may be presumptuous to compare the medical profession with entomology; however, leaving the medical profession and taking a pragmatic view, who really cares about insecticide resistance management?

Agrochemical industry shows concern through such groups as IRAC (Insecticide Resistance Action Committee), but they are not in the best position to do anything about it. Indeed, the development of resistance to insecticide products of one company spells a marked opportunity for all the other companies. The decline in efficacy of one product is actually a positive development in a capitalistic sense, therefore:

Resistance is a Market Opportunity
Do researchers care about resistance? Many of them do, but there is very little a researcher can do about it when the main resistance management tactic has to do with changing insecticide use patterns.

Do environmentalists care? The answer to this, surprisingly, is yes. Environmentalists are very sensitive to the threat of insecticide resistance facing growers. In this they are joined by their colleagues in the government to a certain extent.

The current way EPA operates allows some leeway for registration of materials, even undesirable materials, if there are no alternatives. The regulators are a little like growers in this arena, however, because one gets far more response if resistance can actually be documented.

Resistance management is a concept that is easy to grasp, now widely understood, and everyone cares about it because:

Resistance Management is Popular
Then why don't we have more of it? This is worth thinking about. The simple answer is there are only a few cases of an imminent collapse of production of a commodity that would call for some kind of organized response. In my experience, grower's do not clamor for these sorts of things unless it is recognized that they have a genuine calamity on their hands.

Resistance management is a critical matter to the two players of the game, growers and insects. Growers are the only ones who ultimately make the decision to manage resistance. After all, they are the ones buying the insecticide and applying the selection pressure to the pests. No one else has a prayer, in fact, no one else has any business doing anything about it.

One key difference is liability. M.D.s can be blamed legally if they prescribe the wrong medicine and cause bodily harm. Growers, as a rule, don't sue entomologists if resistance occurs. Indeed, the best advice of entomologists is all too commonly ignored by growers.

Larry Pedigo recently suggested that agriculture consider prescriptions for pesticides much like the medical profession (American Entomologist, Fall 1992). While this is an interesting idea, I can't help thinking one of the many advantages the entomologist has over the physician is the lack of a need for malpractice insurance.

Indeed, the growers have few recourses for redress if they lose a crop. It is, after all, the growers who directly suffer if resistance occurs and that leads to our first conclusion:

Growers are Responsible for Resistance and Management
The second conclusion is that if resistance is a problem, it is a warning flag that insecticides are being used incorrectly, and the answer might be switching to another type of pest management strategy:

If Resistance Occurs at all then IPM has Failed
The third conclusion might take a little more explanation. Resistance management is not a legitimate research area. It is insecticide efficacy testing. In the end, research on resistance management doesn't really produce any new answers to pest problems. Perhaps even worse, because resistance can be measured, we tend to take time to do that instead of looking at the overall pest-crop complex, which is far more difficult, to find solutions, therefore:

Resistance Research is Flawed
This all comes back to a need to refocus on the main and often forgotten subject: Insects are difficult to control. Insecticide use is just one tool we have in this process of figuring out how to protect crops. The tremendous advantage offered by chemical control is that it is quick and certain. It buys time to study a given pest problem more closely and find more lasting solutions.

This was never more clearly demonstrated than in the present whitefly problem.

In my opinion insecticides are still the miracles they were when they were first discovered, and do not deserve to be vilified the way they are currently. We have come to take them for granted in the furor over the environment.

I mourn for the field of insect toxicology which doesn't exist anymore. It strikes me that agrochemical industry has been too busy collapsing and condensing to notice what has happened in Land Grant Universities which are in a bad way.

It strikes me as completely stupid that the nation answers the present crisis in pesticide resistance by pulling money out of the very field that is in the only position to understand the problem fundamentally and do something constructive about getting to answers.

What bothers me most about resistance management is that it is perceived as some kind of a solution to a problem when in fact it tends to preserve the status quo of chemical treatment of pests. By focusing on resistance, we tend to lose sight of the basic fact that insects are difficult to control. We also lose sight of the fact that sometimes using insecticides tends to hide bigger problems, or worse, to cover up simpler solutions.

Acknowledgment : It has been my good fortune to be supported by the California Cotton Pest Control Board for the past several years for research on cotton pests.

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