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Pest arrest in Manhattan, Kansas.

The American grain industry, listening carefully to its domestic and overseas customers, admits there's a challenge out there. The challenge is to meet the ever-more-exacting demands of today's wheat market at a time when chemical pest controls alone are clearly not the answer. Instead, scientists are drawing upon greater resourcefulness and creativity than ever as they step up their struggle against some of agriculture's oldest (and smallest) enemies - insects and microorganisms that invade our crops.

Many of these innovative efforts are in progress at the U.S. Grain Marketing Research Laboratory in Manhattan, Kansas.

Saying No to Granary Insects

Put even a small amount of wheat in storage, and an assortment of insect pests is going to come to call.

Grain producers can fend off some storage pests with a natural soil bacterium called Bacillus thuringiensis (Bt), which has been used against crop pests for more than 30 years. The bacterium forms crystalline proteins that contain an array of insect toxins that are sprayed on stored grain to ward off the pests.

William H. McGaughey heads the Biological Research Unit at Manhattan, which focuses on stored grain insects. A team is now studying Bt's toxic proteins and how they affect target insects.

"Each variety of Bt produces a unique array of toxins that determines which pest insects it will control," explains McGaughey. "But we are finding that insects can become resistant to Bt and survive on treated grain."

So McGaughey and colleagues are tracking down the mechanisms that determine the specificity of the toxins and enable pests to adapt to the Bt toxins. Once they understand these mechanisms, the scientists hope to engineer Bt strains that will be toxic to a wider range of insects and more resistant to insect adaptation.

Others in the research unit are looking at the biological, physiological, and genetic makeup of insects - clues that will help in development of alternative pest control methods.

ARS chemist Karl J. Kramer and molecular biologist Brenda Oppert, along with Thomas D. Morgan, a technician, have found that certain proteins cause a vitamin deficiency or inhibit the digestive enzymes of stored grain pests such as the red flour beetle and the European corn borer.

"In effect, these proteins give the pests a severe stomach ache and eventually kill them," says Kramer.

That work, conducted in cooperation with Kansas State University and the Des Moines-based seed company Pioneer Hi-Bred International, focuses on combining several of these natural compounds to maximize their effect on the insect's gut.

One goal is to transfer the genes responsible for the insect growth-inhibiting compounds into crops. Crops containing these genes would appeal to pests less but would not affect human and livestock digestion.

Avidin and streptavidin, two proteins that bind to biotin, or vitamin H, may also inhibit stored grain pests by interfering with their nutrition.

"Without biotin in the diet, insects cannot grow and develop properly," Kramer says. "Of all the potential insecticidal proteins tested so far, the biotin-binding ones show the most pronise."

They plan eventually to incorporate the avidin or streptavidin gene into plants and test to see whether the plants resist the insects.

Another approach to protecting stored grain is to find ways to weaken the outer covering of an insect - the exoskeleton - so that it cannot survive in the stored grain.

Kramer and Kansas State University colleague Subbaratnam Muthukrishnan note that specific natural enzymes enable insects to molt.

"Our long-term goal is to control stored-grain insects by manipulating either molting enzyme activity, the expression of the genes responsible for molting, or both," says Kramer.

Another potentially useful genetic toll is a maternally acting lethal genetic system discovered in 1991 by ARS entomologist Richard W. Beeman and KSU colleague Rob Denell.

In this system, if a certain gene is carried only by the male insect parent and passed to its offspring, that gene does not affect offspring survival. But if the gene is carried only by the female parent insect, those offspring that do not inherit the gene die. [See "Maternal Gene Life or Death for Flour Beetle," Agricultural Research, January 1993, p. 23.]

The scientists are hopeful the gene may one day be useful as a biological control agent. Biocontrols such as these are becoming increasingly important as the use of synthetic organic chemicals is restricted.

Pilot-scale Elevator Unique in

USDA Research

In other studies by the engineering unit, the Manhattan lab's grain quality elevator facility is used to develop and test new procedures for reducing grain damage through better drying and handling procedures. The pilot-scale elevator located at Manhattan is the only one in the USDA system.

"The major concerns in long-term grain storage are insect and fungus damage, which are highly dependent on grain temperature and moisture," says agricultural engineer Cheng S. Chang.

Having available the means to predict when grain temperature and moisture will become a problem would help grain handlers know when to aerate or fumigate. And keeping grain uniformly cool and dry is one of the best nonchemical means there is to keep it clean and edible.

The Manhattan grain elevator is also used to develop and test more gentle ways to move and handle grain. Breakage during high-volume handling is a major quality concern for all grains, especially for corn.

Computer Programs Help Make

Bug-Control Decisions

Managers of stored grain facilities will soon be getting help from experts who are writing programs that can decide if and when chemical treatment is needed.

One such program, called an expert system, mimics the problem-solving ability of a human expert - in this case, a manager of a stored grain facility. It's been designed to predict what is likely to happen in grain bins under different storage conditions.

The computer program uses models based on several variables to forecast insect population growth in stored grain.

Users provide information such as the planned storage duration, initial grain temperature and moisture, and whether the grain will be aerated. In return, the expert system advises how long the grain can safely be stored. It may also alert a manager to potential problems and suggest changes to avoid or limit insect infestations.

"The expert system can predict storage problems specific to each situation," says ARS biologist Paul W. Flinn, who developed the system in collaboration with David W. Hagstrum, an entomologist.

The expert system is also designed to help farmers or grain managers identify insect pests that may be prowling their grain bins. It inquires about the size of the insect, body color, and other physical attributes. Based on the responses, the system narrows the field of possible culprits to a few insect species and displays a picture of the probable pest on the computer screen.

The program also provides information about how to sample grain for insects and sets thresholds to determine when enough insects are present to require fumigation.

"A person can really learn a lot about grain storage management just by using this system," Flinn says.

The system is currently being field-tested to check the accuracy of its predictions and recommendations, and it's being adapted for use by commercial grain storage facilities. Although the programs were written for stored wheat, a few minor changes will make it useful for other grains.

Flinn says the expert system, which runs on either Macintosh or MS-DOS computers, will be available by early 1994. Plans are to make the program available through ARS and possibly local Cooperative Extension Service offices at minimal cost.

Meanwhile, the Manhattan scientists are also gathering information about stored grain pests' feeding habits by listening to the insects as they munch their way through grain kernels. [See box.]

Data from acoustic sensors may eventually be fed into the expert system to allow more accurate predictions of safe storage life, says Hagstrum, who heads the research project. Hagstrum and Flinn are working to couple the acoustic sensing system with the expert system.

Breeding Problems Out

For scientists who breed wheat, the first line of defense against pests begins long before a variety is ever planted.

In the Plant Science and Entomology Research Unit located on the campus of nearby Kansas State University, Merle G. Eversmeyer leads a team of researchers who develop new hard red winter wheat germplasm - types of wheat that carry natural resistance to the Hessian fly, leaf and stem rust, and other pests.

It's an effort that requires patience, for it can take as much as 15 years of breeding to produce a new wheat variety for release to growers. But the effort pays off when it yields a healthy wheat that delivers a high-quality kemel to the marketplace.

One member of Eversmeyer's group, ARS entomologist J.H. Hatchett, has conducted cooperative research with KSU scientists showing that x-rays will break wheat and rye chromosomes. This key discovery enables genes from rye - which is highly resistant to Hessian fly - to attach to wheat chromosomes. [See "Wheat Tough Enough To Take the Hessian Fly," Agricultural Research, September 1991, pp. 22-23.]

The result: wheat that can foil the hungriest Hessian fly.

Public and private plant breeders can obtain seed for use in breeding this valuable trait into commercial wheat varieties from the Wheat Genetics Resource Center, Department of Plant Pathology, at Kansas State University.

Another notorious enemy of top-quality, top-yielding wheat is leaf rust, a fungal disease that attacks wheat and hinders seed formation, lowering yields. The disease can also depress protein content.

ARS wheat breeders have found ways to endow plants with genetic resistance to leaf rust. Genes from three subspecies of a type of wild wheat, Triticum monococcum, "appear to be very effective against rust," notes Thomas (Stan) Cox, a wheat geneticist in the Plant Science and Entomology Research Unit. Working with KSU scientists, Cox crossed T monococcum with common wheat, creating three new breeding lines with the desired genes.

One of the lines has already been released to plant breeders; the remaining two with rust resistance will undergo further testing before release.

The rust-resistant line was the eighth wheat genuplasm released to wheat breeders since 1986 by the ARS-KSU joint project.

But not all insects are bad news, the scientists note. Beneficial insects such as parasitic wasps may one day help grain managers control infestations.

One such wasp, Cephalonomia waterstoni, sometimes already found in small numbers in grain bins, moves through a storage facility looking for beetles to parasitize, much like a detective might stalk and capture a suspected criminal.

Ralph W. Howard, an ARS chemist, wants to know just how these beneficial wasps track down their victims and how they know when they've found the right one.

Grain beetle larvae feed on the inside of a wheat kernel and emerge when they're ready to pupate or form a cocoon.

But before the larvae settle into the pupal stage, they wander through the grain mass looking for a place to cocoon, leaving a faint chemical trail behind. The wasp follows one of these trails until it finds a larva, paralyzes it with a sting, and then lays eggs on it.

"It appears that the beetle unwittingly leaves this trail that ultimately leads to its demise," Howard says.

Flinn and Hagstrum are developing a method to mass-rear the wasps and make their use in grain facilities a reality.
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Title Annotation:US Grain Marketing Research Laboratory's pest-control research
Author:Gerrietts, Marcie
Publication:Agricultural Research
Date:Jul 1, 1993
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