Some species of thrips are insect pests of flowers, ornamentals and agricultural crops. But a few are beneficial as predators of mites and insects and as pollinators of crops. University of Florida and ARS scientists showed for the first time how thrips pollinate West Indies mahogany tree flowers in Florida. These hardwood trees from the tropics are grown for their valuable wood. They also are favored ornamentals along roadsides. ARS research identified five species of thrips that were the only insects found in 12 to 59 percent of mahogany tree flowers collected from seven sites located many miles apart. Pollen coated their bodies, providing the first evidence that some thrips help cross pollinate mahogany trees. Further studies are needed to find out how effective these insects are as pollinators over the long run. Since little was known previously about pollination of this valuable tree, this information increases understanding of how mahogany trees are pollinated and could be used by scientists worldwide who work on breeding better mahogany trees.
Systematic Entomology Laboratory, Beltsville, MD
Sueo Nakahara, (301) 504-6893

A search for genes that enable a corn plant to "starve" leaf-eating fall armyworms has been narrowed by ARS and Mississippi State University scientists. Their ultimate goal is to genetically engineer commercially available corn hybrids so they too can have this built-in pest protection. Recently, the scientists determined that the gene they seek is Mir1, responsible for making the protein 33 kD cysteine proteinase. When hungry armyworms munch corn leaves and ingest the protein, they may stop growing or starve. The scientists hope to insert the protein-making gene into susceptible corn hybrids or other crops that are targets of hungry armyworms and other destructive caterpillar pests. The researchers isolated Mir1 from the tissue of a worm-resistant corn line, Mp 708. They then made millions of copies of the Mir1 segment. This helped them identify nearly all the nucleotides--or individual chemical constituents--comprising Mir1. The scientists then inserted the Mir1 segment into bacteria for use as microbial workhorses in studies of the protein's effectiveness. Besides armyworms that attack corn, the genes may someday quell the appetite of other lepidopteran pests of other crops.
Corn Host Plant Resistance Research Unit, Mississippi State, MS
W. Paul Williams, (601) 324-2735

Romance could turn deadly for amorous pecan weevils. ARS and Oklahoma State University scientists--for the first time--have identified the weevil's chemical sex attractant, or pheromone. This could lead to a commercial pheromone that pecan growers could deploy to monitor weevil populations or to disrupt weevil mating. Prospective mates either couldn't find each other or would be lured to doom in traps. In lab and field studies, a synthetic version of the male weevil's pheromone attracted 80 percent of females. Chemical insecticide sprays are now the main recourse for protecting pecan orchards. Unchecked, the weevils chew on young pecan nuts, ruining their marketability. In late summer, female weevils bore into nuts to lay eggs. Soon, larvae hatch, drop to the ground and burrow into the soil. Two to three years later they emerge as adults and start the cycle again. University scientists are awaiting results of large-scale field tests of the synthetic attractant in orchards this past summer. ARS is considering patenting the use of the weevil pheromone.
Crop Science Research Laboratory, Mississippi State, MS
Paul Hedin, (601) 323-2230

"Squash 'em!"--but not literally. That's the advice of ARS scientists who showed that squash plants will lure cucumber beetles and squash bugs away from more valuable crops like watermelon and cantaloupe. The tactic could be a new way to reduce insecticide sprays on the melons. Since squash is the insects' favorite cucurbit, they will feed on it first. In spring, growers typically spray plant seedlings with insecticide two to three times. But they could use less insecticide by planting one or two rows of squash as a "trap crop" around the field's perimeter. In experimental watermelon and cantaloupe plots, the tactic lured up to 66 percent of a plot's total population of the insects. The attraction was fatal for 90 percent of them, because the scientists sprayed insecticide only on the squash perimeter of a plot. Commercial growers in Texas and Oklahoma are helping the scientists run large-scale field studies. In the Midwest, the approach could also help stop cucumber beetles from spreading a bacterial disease, cucurbit wilt, through the melon patch.
Southcentral Agricultural Research Laboratory, Lane, OK
Sam D. Pair, (405) 889-7395

Four new ARS corn germplasm lines could eventually supply corn farmers with new varieties that curb the appetite of harmful, worm-like organisms called nematodes. ARS scientists developed, tested and have released the new corn lines to plant breeders and other researchers. The lines are Mp 709, Mp 710, Mp 711 and Mp 712. Each withstands the southern root knot nematode, Meloidogyne incognita, and peanut root knot nematode, Meloidogyne arenaria. Both pests are prevalent in the southeastern United States and primarily infest sandy soils where they tap vital nutrients from corn plant roots. This can cause yield losses of up to 30 percent. The new resistant corn plants squelch such feeding, though scientists don't yet know how. In greenhouse tests, the scientists applied 3,000 nematode eggs to seedlings of both the resistant lines and a susceptible check called Ab24E. After 60 days, they counted the eggs that remained. Using a rating index of 0 (for no egg masses) to 5 (for more than 100 eggs masses per plant), they found Mp 709 was most resistant, rating 0.1. Second best was Mp 710, at 0.9. The susceptible check earned a 3.5 rating. Scientists say the lines' yield and other agronomic traits can be improved through cross breeding with commercial corn.
Crop Science Research Laboratory, Mississippi State, MS
W. Paul Williams/Gary L. Windham, (601) 323-2735/2230

Two plastic mulches are controlling nutsedge, one of the 10 most common and troublesome weeds in Florida vegetable crops. Few chemicals other than methyl bromide--which has been identified as an ozone depletor and is slated to be banned in 2001-- are available to control nutsedge. In both greenhouse and field experiments, ARS scientists significantly suppressed purple nutsedge by using photoselective infrared transmitting mulch films and silver mulch films. More research is planned on how these mulches work to suppress the weeds.
U.S. Horticultural Research Laboratory, Fort Pierce, FL
David T. Patterson, (407) 467-3081

Researchers are genetically altering tomato plants to resist attacks by microscopic worms called nematodes. Tomato growers now use methyl bromide to rid the soil of nematodes and other harmful organisms. But methyl bromide--probably the most widely used pesticide in the world--has been identified as an ozone depletor and is scheduled to be banned in 2001. Several tomato genes play a role in providing nematode feeding sites. Researchers have linked these genes to a genetic switch that is turned on when nematodes start to feed. Tomato plant cells that now serve as feeding sites for root knot and reniform nematodes will malfunction, eliminating the pest's food source. The ultimate goal: Tomato plants that will produce more and larger fruit without using methyl bromide.
U.S. Horticultural Research Laboratory, Orlando, FL
David T. Kaplan, (407) 897-7300

Tomatoes infected with a newly described virus, tomato chlorosis, should now be easier to diagnose. ARS virologists developed a test that determines within 24 hours whether a plant has the virus. It's transmitted by four species of sap-sucking whiteflies, major pests of tomatoes and other crops. The University of Florida's plant disease clinic in Gainesville is now using the ARS test on leaf specimens sent by growers. Florida produces more than a third of the nation's $460 million tomato crop. The clinic's researchers will also use the new test to identify weed species that are vulnerable to the virus. Whiteflies may be carrying virus from those weeds to nearby tomato fields. The test relies on molecules, called nucleic acid probes, that detect the virus' genetic material. These are the first such probes for this virus. ARS scientists and their clinic colleagues were the first to describe and name the tomato chlorosis virus. It causes leaves to yellow and thicken, and plants to produce fewer and smaller fruit. The ARS tests indicate that greenhouse, banded-wing, sweetpotato and silverleaf whiteflies all can transmit the virus.
U.S. Agricultural Research Station, Salinas, CA
James E. Duffus/Gail C. Wisler, (408) 755-2835

ARS scientists have tentatively classified a bacterium that's helping control the citrus root weevil in Florida citrus groves. The weevil, which can cost citrus growers more than $1,200 per acre, has already caused an estimated $72 million loss to Florida's economy this year. The beneficial bacterium is produced by microscopic worms called Steinernema riobravis nematodes. Preliminary tests indicate the bacterium may belong to the genus Xenorhabdus. The S. riobravis nematodes are sprayed onto the soil and burrow down to tree roots, where they find and parasitize citrus root weevil larvae. Once inside the larvae, the nematodes release the bacteria, killing the larvae within 48 hours. The nematodes reproduce inside the larvae and the offspring are nourished by the bacteria, which also release antimicrobial agents that prevent the growth of other bacteria, eliminating competition. Scientists are investigating other natural "carriers" that might develop a similar symbiotic relationship with the bacterium and thus become another potential biological control agent for the citrus root weevil, which has also become a significant threat to ornamental and vegetable crops.
U.S. Horticultural Research Laboratory, Orlando, FL
William J. Schroeder/Heather Smith, (407) 897-7300

A new ARS-developed peach rootstock could offer an alternative to using the pesticide methyl bromide to rid the soil of nematodes that cause peach tree short life (PTSL). PTSL is a major problem for peach growers throughout the southeastern United States. Scientists with USDA's Agricultural Research Service developed the new rootstock--in conjunction with Clemson University researchers--to resist the ring nematode that leads to PTSL-related tree death. ARS scientists have recently found that this rootstock also resists the root-knot nematode, which causes reduced tree growth of young trees. Called Guardian™, the new rootstock is now available at commercial nurseries as bulk seed for next year's growing season.
Southeastern Fruit & Tree Nut Research Laboratory, Byron, GA
Andy P. Nyczepir, (912) 956-5656

A new technique cuts out the need for an insect "middle man" to transmit insect transmitted plant viruses. Insects traditionally have been used as vectors to transmit viruses to plants, a method requiring special skills to rear and manipulate an insect population. Researchers have shown they can transmit all major insect-obligate corn viruses by using insect pins . The pins are pushed through a drop of virus into the vascular system of the corn seed which has been soaked in water. Transmission rates in plants from inoculated seeds are similar to the rates achieved using insects as vectors. The new method will help reduce research delays and disruptions caused by using insects and make it easier to evaluate virus resistance in corn worldwide.
Corn and Soybean Research, Wooster,OH
Ray Louie, (330) 263-3836

Wheat breeders who think they're closing the door on one type of leaf rust problem may be opening the door to another. In their attempts to develop wheats with resistance to Puccinia triticina, the leaf rust that attacks wheat, breeders have "borrowed" genes from rye and wild grasses related to rye. Previously, wheat leaf rust and rye leaf rust were thought to be caused by the same fungus, Puccinia recondita. Now ARS scientists have shown that rye leaf rust and wheat rust are caused by two distinct fungus species, P. triticina which attacks wheat and P. recondita, that attacks rye. By transferring genetic material from rye or a wild rye relative to wheat, the breeders could be creating new wheat varieties which are susceptible to P. recondita and P. triticina both types of rusts. In addition, triticale, a hybrid of wheat and rye may be vulnerable to both types of leaf rust.
Cereal Rust Laboratory, St. Paul, MN
Kurt Leonard, (612) 625-5786

Estragole, a natural chemical found in leaf oil in some varieties of avocado, kills the Caribbean fruit fly. ARS scientists first discovered and reported that the compound is toxic to insects. They've found it in varying concentrations in the leaves of 14 varieties of Mexican avocados--but none in the seven Guatemalan and 13 West Indian types of avocados tested. Further research is needed to genetically manipulate the gene responsible for producing estragole to give plants natural resistance to the Caribbean fruit fly and possibly other insect pests. Malathion is now used to control this fruit fly, but environmental and health concerns have been raised about the chemical. Scientists and industry are looking for a replacement.
Subtropical Horticulture Research Laboratory, Miami, FL
Jimmie R. King, (305) 238-9321

Leaf hairs on the surface of wheat plants may protect the crop against fungal infection. ARS scientists used a scanning electron microscope to demonstrate that wheat plants with greater leaf pubescence--hair-like structures on the leaf surface--are less susceptible to fungal infection. When a fungal spore lands on a leaf surface, it sends out a germ tub or "root" to penetrate the stomate--a small pore in the leaf surface--that enables the plant to exchange carbon dioxide and oxygen. If plant surfaces are covered with leaf hairs, the spores become entangled in the maze of hairs and die before they can penetrate the stomate. Scientists say wheat plants might be bred to have more leaf hair, deterring fungal infection.
Cereal Rust Research Unit, St. Paul, MN
Dave Long, (612) 625-1284

A fungus-killing compound from oats could be the key to stopping the water-borne mold Aphanomyces from inflicting millions of dollars of damage on the edible pea crop every year. Researchers have isolated the compound, called avenacin. It's produced by the living oat plant but becomes toxic to the fungus when the plant is injured, such as by being tilled under, and stays in the soil even after the oat plant dies. Saratin kills spores of Aphanomyces before they can complete the fertilization process. For effective biocontrol, scientists recommend pea growers plant oats in a rotation and till in the stalks after harvest, or as a second crop in the fall, then chisel-plow the green crop into the ground. A new crop of peas planted on the same ground the following spring would reap the benefits of avenacin. Another plus: Oats used as a biocontrol for the fungus also encourage soil-saving conservation tillage, as avenacin must remain in the top 4 inches of soil to be effective. Research shows moldboard plowing and traffic-induced soil compaction contribute to the spread of Aphanomyces.
Soil and Water Management Research, St. Paul, MN
Ray Allmaras, (612) 625-1742

Last Updated: January 28, 1997
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