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Nematodes Fight Biobattle Against Biting Flies

Flies that pester cattle in the feedlot could meet their match in tiny parasitic roundworms now being tested as biological control agents by a pair of Agricultural Research Service (ARS) and University of Nebraska-Lincoln (UNL) scientists.

ARS entomologist David Taylor says their research aims to find out whether the roundworms, or nematodes, can provide cattle producers with a reliable alternative to chemical insecticides, which often must be reapplied as fly populations rebound or migrate in from other sites. In the nematodes--which includes the species Steinernema feltiae--Taylor and UNL associate Thomas Powers also see a way to delay the emergence of insecticide-resistant fly populations.

Nationally, flies cost the beef and dairy cattle industry up to $1 billion in annual production losses. The chief targets of Taylor and Powers' research are house and stable flies, especially the latter. Attacks by swarms of the relentless biting flies on cattle cause blood loss, stress and feed-efficiency problems. Both fly species can also be a nuisance to animal handlers and homeowners whose properties are close to cattle operations, notes Taylor, with ARS' Midwest Livestock Insects Research Unit in Lincoln, Neb.

Since 1999, the two researchers have screened about 20 species and 50 strains of fly-infecting nematodes. Of special interest are those capable of surviving in manure around feedlots or soiled bedding in calf pens, where 80 percent of the flies' brood hatch and feed. The nematodes kill the flies' maggot offspring by wriggling into their bodies to feed, mate and reproduce. In experiments, up to 99 percent of fly maggots died within 48 hours of infection by S. feltiae, the researchers' top fly-fighter.

A more in-depth article about this work appears in the July issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's chief scientific research agency.