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Pioneering Entomologist Battles for Biological Control in Agriculture

BY DAN IMHOFF

Farmer to Farmer, July 1994

To Everett Dietrick it's a bug eat bug world. For more than forty years he has been a devoted student of the natural enemy complex, and an ardent practitioner of biological controls in California agriculture. As a researcher for the U.C. Riverside Department of Biological Control from 1947–60, Dietrick participated in much of the pioneering work accomplished in beneficial insect management still in use today. Dietrick left the university in 1960 to launch a career in the private sector, co–founding Rincon Insectaries Inc., California's first commercial insectary. Since that time he has provided farmers with insects as well as farm management skills, in an effort to limit chemical usage to minimal applications of soft pesticides. Farmer to Farmer spoke to Everett Dietrick by phone at the Ventura office of Rincon–Vitova, where he serves as president and still puts in 50 hour work weeks, monitoring fields for such clients as Gallo and Pavich Farms, and selling generalist parasites and predators over the counter.

The parasitic wasp Hyposoter exigua lays its egg in a beet armyworm. The larva that hatches will grow inside the worm, killing it before it emerges.

How would you summarize your theory of biological control?

It is the regulation of pest populations by natural enemies, such as predators, parasites or pathogens that attack pests and compete for food and space with potential pest species. These organisms interact in specific ways that work in balance with nature.

There's a basic rule at work with biological controls: the more you hit nature with a pesticide, the harder it will come back at you. If you kill 95% of a given species, the remaining 5% will come back to haunt you. Resistance is the way nature fights back. A pesticide is good as long as it controls most of the insects. But when you get resistance and control failure, you're making money for the pesticide company, not the farmer.

Are there different types of biological control?

There are basically three: ( 1 ) classical, or the importation of exotic species and their establishment in new habitats; ( 2 ) augmentation of established species through direct manipulation of their populations, as by insectary mass production and periodic colonization; and ( 3 ) conservation through habitat management favorable to the survival and nurturing of naturally occurring predators, parasites and entomogenous pathogens.

Complexity seems to be at the heart of your theories of biological control. How would you describe this concept?

Complexity is what is necessary to biological control. This is why planting cover crops to increase diversity is so important. Cover crops and mulches can overcome the monocultures of modern farming. When you destroy diversity with plowing and cultivation to expose the soil to the sun, you destroy diversity and in crease dependency on pesticides.

Maximizing diversity of plants and minimizing interference from excessive pesticides, ants, dust and farming practices that destroy habitats for beneficials results in more effective biological control. The real proof for biological control lies in the many crops which are being marketed organically and are free of any pests or pesticide residues.

Do you know of any particular models where beneficial control has been effectively used over a long period of time?

When I first started my business in 1960, I modeled it after the Fillmore Citrus Protective District, in Ventura County. As far back as the 1940s, these farmers owned an insectary and hired entomologists to grow insects and monitor their orchards. They have 9,500 acres of citrus and have never sprayed more than an average of one time per acre per year in over half a century. When you have that much acreage you have many problems–ants, scale, road dust. They have a program of augmentation. Several species of beneficials are grown in the insectary and are regularly released to augment natural enemies. The idea is to nurture the biological control on these farms.

How does a farmer make the switch to biological controls?

The change comes when someone is dissatisfied. Either their spray program is too costly or ineffective or there are health problems. At that point the farmer needs a plan to back away. You don't quit tomorrow. If you don't have beneficial insects on your farm then you have to establish habitat and introduce them through insectary or field–harvested sources. It takes time but you can make these biological controls work on the farm.

What advice do you have to farmers interested in starting with biological controls?

You start with growing healthy plants in living soil. Then I encourage farmers to grow refugia. These are planned reservoirs of good bug species that can be maintained on a farm by fostering mulches and unsprayed cover crops– particularly legumes and many resident weeds. You strip cut the refugia to keep it young. Don't let it mature. Insects leave crops when they mature, looking for the next planting or host cycle. With refugia, a field always comes under biological control eventually and the spraying of hard pesticides can be reduced or eliminated. Begin with a portion of a field to get experience and find a PCA who is dedicated to your focus.

 

TYPES OF BIOLOGICAL CONTROL

Biological control comes in three forms:

(1) classical, or the importation of exotic species and their establishment in new habitats; (2) augmentation of established species through direct manipulation of their populations, as by insectary mass production and periodic colonization; and (3) conservation through habitat management favorable to the survival and nurturing of naturally occurring predators, parasites and entomogenous pathogens.

An adult green lacewing, Chrysoperla carnea. This general predator feeds on a wide variety of pests in the larva stage.

How exactly do these refugia work?

Borders of cover crop refugia attract and grow the numerous biological control systems needed to regulate the total complex of pests affecting all vegetable and field crops. No season is ever the same nor does any biological control system function the same in location or time. Constant monitoring and management of the system is required to make the most of beneficials.

Where does augmentation by releases of beneficials raised in insectaries come in?

Some augmentation is useful because insect cycles are worse some years than others. The only reliable sources for some beneficials are insectaries.

I read that you once referred to lacewing larvae as the DDT of the insect world. What are some of the most common lacewings?

There are many species of both green and brown lacewings. The most widely distributed species that insectaries produce is Cbysoperla carnea. This species is resistant to most pesticides, because the mother stock is taken from heavily sprayed farming areas. Brown lacewings are more active in winter and cool weather areas but are not cultured. Mass production of C. comanche and C. rufilabris are the only other ones that are marketed.

You worked with one of the founders of the Integrated Pest Management movement, Robert van den Bosch, at U.C. Riverside. What were some of your findings?

In 1953 1 began to assist Robert van den Bosch on a field crop survey. This was most exciting because up until then, biological control was thought to work only on tree crops or perennials. We were studying the "alfalfa/cotton complex." We found that you didn't have to spray cotton because the alfalfa insects would control cotton insects if they were next door to each other. As long as you strip cut the alfalfa, that is. The old equipment didn't move that fast and it took a long time to cut alfalfa. This slow gradual cutting of alfalfa kept the cotton pests in check in the alfalfa. The change to modern machinery has greatly increased the speed of work. Today you cut all the alfalfa in one week and all the pests go into the cotton seeking food. So you have to spray the cotton the next week. We reported our findings in 1960. This applied to many other crops, including vegetables.

Can you describe your early studies on citrus and avocados at the U.C. Riverside Research Station?

I spent five years with Dr. Paul DeBach researching citrus and avocados. Among many other studies, we were colonizing the vedalia beetle as a possible control for the cottony cushion scale. We found that repeat applications of DDT interfered with the vedalia ladybug. All we had to do was stop spraying DDT and we could manage the problem because DDT didn't kill the cottony cushion scale, but it did kill its natural predators. It was a classic success story of biological control. The vedalia beetle is still the natural enemy of choice today.

How would you direct current research efforts?

Our research should be concentrated on those pests for which we presently have no biological controls: black flea beetle, cucumber beetle, pink bollworm and fruit flies. There isn't the economic support to do this classical research. If the pink bollworm were brought under biological control you wouldn't have to spray cotton anymore. Of course that would mean a multi–million–dollar loss for the chemical industry.

What are some of the factors working against biological controls at the moment?

Fear. Difficulty in understanding complexity. Misinformation. A lack of faith in the system. I disagree with some organic farmers that healthy soil is the most important key to warding off pests. Of course healthy plants and healthy soil can ward off pests and disease. But what is most important in my mind is the ratio of good and bad bugs. This is so crucial. You want a high ratio of beneficials even with a low insect population. Fields are kept free of pest problems because of the complexity of biological systems. The concept may appear chaotic, but it is so simple.

How do you answer criticisms that using beneficial insects is a step back in time, where the farmer is unarmed against pests?

We're stepping way out in front because we know what is necessary now. Look at Europe where they are using very sophisticated biological control systems in greenhouses. They came to us in the 1950s to learn about biological control. Now we're the last to benefit from this knowledge.

I believe that somewhere in the world there is a natural enemy system that will manage insects and we need to spend a lot more time working with these complexes. Sooner or later the sprays are just not going to work and we're going to have to provide a refuge and learn to manage these insects with a minimum usage of soft pesticides that do not create more pest problems.

What are your visions for California agriculture?

My vision is for less and less spray. The only problem I see is fruit flies or the invasion of some other exotic pest and the consequences of eradication attempts. If the state tries to eradicate it with malathion they'll destroy all the progress we've made in a futile effort to satisfy a political problem. The world should learn to live with the fruit fly and find a way to keep it in check with biological controls and selective soft pesticides. With the $30 million annual eradication budget for the Medfly we could develop a focused search for biological controls and permanent solutions.

Prior to DDT most crop pests were controlled by natural enemies. Alfalfa hay was never sprayed and cotton only received occasional dusting for mites. I have witnessed the initial success and resulting failure of conventional pesticides to control resistant pests. The increasing numbers of new pest situations from insects which were previously secondary minor pests creates the need for an ever–increasing cycle of repeated applications of more and diverse sets of poisons. This pesticide treadmill destroys more and more predators and parasites, increasing the numbers of formerly minor pests, which are now becoming super–pests–resistant to all registered pesticides. Biotechnology is presently creating the next set of pesticides of genetically altered plants carrying resistance factors. Instead of seeking real biological control they seek to inflict more simplistic answers that will ultimately fail due to resistance development to these products. We are unsure of what other different problems will come from this technology.

General predators such as this big–eyed bug (Geocoris punctipes) feed on many pests in a wide variety of crops, in both adult and nymph stages.

At the same time myths about organic agriculture are perpetuated in a continuous propaganda campaign. They imply that organic yields are much lower and the cost of labor is much higher and the products are damaged. In short, we'll starve if we don't spray. I have witnessed many innovative organic production systems that are thriving throughout the world. We should be asking ourselves, "What steps do we have to take to get off total chemical systems and the pesticide treadmill? How long will it rake? What are the costs of the transition?"

The wonderful thing about biological control is that it's always progressing, always different. It is constantly fascinating to observe agriculture in the absence of pesticides. My goal is to eliminate the need for most broad–spectrum pesticides.

 

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