Nematodes: Lords of the Flies?
Biting flies that pester cattle could soon get a taste of their own
medicine. Agricultural Research Service
(ARS) and University of Nebraska-Lincoln (UN) scientists are testing
a way to fight the flies in feedlots where they gather and breed. They're
using tiny parasitic roundworms called nematodes that prey on the flies'
Exploring new, nonchemical ways of protecting cattle is the objective
of a 3-year-old project by entomologist David B. Taylor at ARS' Midwestern
Insect Livestock Research Unit in Lincoln. In nematodes he sees a biocontrol
agent that could be part of an integrated fly-control program at the
feedlot along with traps, manure management, sanitation measures, and
Since 1999, Taylor and UN associate Thomas Powers have screened 20
species and 50 strains of fly-infecting nematodes for their abilities.
Of particular interest were those capable of persisting in cow manure
long enough to kill house and stable fly larvae over an entire season.
In Nebraska, where beef cattle are the top agricultural commodity with
annual sales of $5.5 billion, stable flies are considered even worse
pests than house flies. That's because attacks by swarms of these relentless
biting flies cause blood loss, stress, and feed-efficiency problems.
The flies may also harbor disease organisms, and they cost the U.S.
beef and dairy cattle industry up to $1 billion in annual production
Taylor's and Power's strategy calls for battling the pests in manure
around feedlots or in soiled calf pen bedding. That's where 80 percent
of the flies' brood hatch and feed. And prolific breeders they arehundreds
of maggot offspring emerge from a single pound of manure. Therein lies
the nematodes' appeal, for a mating pair of these roundworms can produce
5,000 to 10,000 offspring in a single maggot in less than 2 weeks. Says
Taylor, "The nematodes actually reproduce faster than the flies."
In experiments, up to 99 percent of fly maggots died within 48 hours
of infection by the top fly fighter, Steinernema feltiae. In
the laboratory, "the nematodes can live in bovine manure for 4
to 6 weeks without hosts," says Taylor. In feedlots, he adds, "We'd
like to apply them in May and get season-long fly control." Chemical
insecticides, in contrast, must be reapplied, and flies can develop
resistance to them.
The researchers are testing ways to apply the nematodes on manure and
protect them from drying and ultraviolet light. About 1 million nematodes
per square meter are used, but lower rates might suffice, keeping the
costs closer to chemical controls. If the approach works, the nematodes
could also be used to fight corn rootworms in manure-fertilized fields,
says Taylor.By Jan
Suszkiw, Agricultural Research Service Information Staff.
David B. Taylor
is with the USDA-ARS Midwestern Livestock Insects Research Laboratory,
Plant Industry Bldg., Room 304B, East Campus, University of Nebraska,
Lincoln, NE 68583; phone (402) 437-5792, fax (402) 437-5260.
"Nematodes: Lords of the Flies? " was published in the July 2002 issue of Agricultural Research magazine.