ITHACA- Poultry and livestock producers may soon benefit
from a biological solution to one of their most persistent headaches, the
so-called " filth fly". Not only does the fly annoy the animals,
but it can also spread diseases such as salmonella, raise harmful bacterial
counts in the cow's milk and contaminate poultry-raising facilities.
Closely related to the common house fly, Musca domestica, the filth fly
lives up to its name by breeding wherever moist organic material is present,
including manure, soil bedding and wet animal feed. It is becoming increasingly
difficult to control
due to developing resistance of the flies to standard insecticides and
because of increasing federal restrictions on the manufacture of the same
pesticides.
A fresh approach to controlling the troublesome pest is a new formulation
of selected strains of a common soil fungus-- called Beauveria bassiana--which
destroys the fly's innards on contact or when the flies eat it. Although
there are high hopes for its use by livestock and poultry farmers, the fungus
is also infamous for the fact that it destroys silk worms and almost wiped
out the American silk industry in the 1860's.
The fly-killing fungal preparation is the product of several years research
led by Donald A. Rutz, PhD, chairman of the Department of Entomology of
Cornell University's College of Agriculture and Life Sciences. After extensively
screening scores of different strains of B. bassiana, they succeeded in
isolating the most virulent strain in 1993.
Since then the Cornell researchers have been incorporating the fungus
into a number of different formulations, some of which contain baits to
lure the flies to their eventual doom. They now know that B. bassiana invades
the fly host either by ingestion or by contact. The flies also pick up the
fungal spores by walking on a surface treated with the formulation and then
spread it over their bodies when they groom themselves.
When the fungal spores germinate , they produce a complex of as yet not
fully-unidentified enzymes which allows them to dissolve and penetrate the
outside surface of the flies' bodies.
Once it has broken through, the fungus replicates and consumes the insect's
internal organs and the hemolymph, a blood like fluid. The Cornell investigators
report that it takes about five days from penetration to death and that
100% of the flies are dead within one week after exposure to the fungal
preparation.
Finally, when the insect succumbs to the biological attack the lethal
fungus emerges through the exoskeleton and produces a white mycelial mat
on the outside of the body. The mycelium-- which contains a new generation
of fungal spores--can then be collected, grown on artificial cell culture
media and harvested for further fly control use, Dr. Rutz explained.
The advantage of the fungal preparation is that unlike standard chemical
insecticides it affects only the flies and does not pose a hazard to the
cattle, poultry or the farmers who raise them. There are still many steps
before it reaches the commercial production stage , but when that happens,
Dr. Rutz believes that the fungal treatment could replace many of the potentially
hazardous chemical insecticides that have been or are about to be withdrawn
from the market, he noted.
