Biological control shows promise in poultry houses
A beneficial wasp on a house fly pupa (magnified). Photo: S. Long
Wherever there are chickens, there is chicken manure, a great habitat for house fly breeding. No one wants to live next door to a "fly hatchery," but expanding urbanization has juxtaposed former "city folk" and poultry producers. Some of these urban neighbors have confronted producers or even pursued litigation over increasing fly populations.
Though flies do not harm chickens, our nation's poultry producers spend millions of dollars each year (e.g., $32.4 million in 1993) in an attempt to rid their poultry houses of them. Many insecticides are either no longer effective or no longer available, reinforcing the need for an integrated approach to managing house flies.
One promising alternative to chemicals entails releasing tiny wasps that kill house flies by parasitizing their immature stages. These parasitic wasps ("parasitoids") are harmless to humans and to poultry and other livestock. Stefan Long, Wes Watson, and Don Rutz, of Cornell, carried out an IPM-funded project in 1996 to release a species of parasitoids called Muscidifurax raptorellus in three poultry houses. They monitored M. raptorellus population growth and took note of impacts on the fly population.
M. raptorellus killed more than 70 percent of immature flies during a nine-week period in poultry houses in which there had been previous releases of biological control parasitoids. Rates were much lower in the poultry house with no history of parasitoid releases: only 26 percent control of the flies was provided by M. raptorellus.
By minimizing practices detrimental to parasitoids, such as applications of larvicides and residual insecticides, growers can enable the wasps to become established in sufficient numbers to control fly populations in poultry houses. Augmentative releases can help beneficial parasitoids become established more quickly.
Several species of fly parasitoids occur naturally throughout the United States. Preferences for climates and for fly breeding materials vary from species to species. One species common to dairy farms and poultry operations is M. raptor, which has been positively evaluated in previous IPM projects.
M. raptorellus has an advantage over M. raptor: its females typically lay more eggs. The average for M. raptorellus is 3-5 eggs per fly pupa. M. raptor females lay only 1 egg per pupa. This potential for more rapid population growth makes M. raptorellus a promising candidate for biological control of flies.
Several privately owned insectaries have recently begun mass rearing of M. raptorellus for commercial use. This tiny biological control agent may soon be helping poultry producers save face, save money, and stay out of court.