Two Parasitic Wasps Show Promise For Controlling Pest Flies

July 15, 1997

CHAMPAIGN, Ill. -- With the goal of improving the natural biological control of flies, scientists have scoured Illinois feedlots. After three years of study, they say that two parasitic wasps known as Spalangia endius and Spalangia nigoraenea are especially important in the Midwest and actually could emerge as weapons.

Such is the finding of a study of parasites that feed on stable and house flies in Illinois. Both types of flies are well-known pests. Stable flies feed on the blood of cattle, annoy other livestock and adversely affect production, and, like house flies, are a public health problem among humans.

Researchers from the University of Illinois collected fly pupae from manure, spilled feed, along fence lines, near water sources and waste piles of straw and hay at feedlots. The scientists then looked for the presence of either emerging flies or the parasites that kill them.

The predominant parasites that kill flies are tiny wasps. As in the movie "Alien," the wasps lay their eggs inside a host, in this case within a fly pupa, killing the host from within. The egg hatches and the parasite larva feeds on the dead fly's pupa before emerging as an adult about a month later.

Spalangia endius wasps, although rare or absent in similar studies in Kansas and Nebraska, were common in southern Illinois. Because these wasps already are reared and sold as a biological control, mostly for use in California and Northeast dairies, they may be worth a closer look as a biological control in Illinois, said U. of I. agricultural entomologist Richard Weinzierl.

The findings were published in the April issue of Environmental Entomology. Working with Weinzierl on the project, which was funded by the USDA and the U. of I., was Carl J. Jones, a U. of I. veterinary pathobiologist.

"In general, endius had been written off as ineffective and unimportant in the Midwest, where we have harsh summers and cold winters. It has been said that we never could release enough to be effective," Weinzierl said. "However, it may be that endius is a potential biological control agent that we should be concentrating on. That could be from the fact that there's a lot of difference in climate between Illinois and the central plains."

The U. of I. study provided the first comprehensive documentation of naturally occurring fly parasites in Illinois. The most common species in Illinois appears to be Spalangia nigoraenea, the same species that dominates collections in other portions of the country. A third species, Spalangia nigra, commonly attacked and killed stable flies in the north, the researchers reported.

The information, Weinzierl said, "gives us some baseline data for comparisons when future biological control measures involve the introduction of new species of parasites." The research is part of an effort to control fly populations more effectively with natural biological enemies because of the flies' growing resistance to insecticides and increased concerns about the health risk of pesticides.
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University of Illinois at Urbana-Champaign

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