Pennsylvania State University researchers have completed a research project funded by the U.S. Poultry & Egg Assn. (USPOULTRY) and USPOULTRY Foundation that investigated the use of biological control agents to decrease house fly populations.
Dr. Erika Machtinger with the Penn State department of entomology and colleagues evaluated the use of parasitoid wasps and the entomopathogenic fungi Beauveria bassiana to see if augmentative releases of these antagonists and the introduction of pathogenic organisms can help lower house fly populations to manageable levels, USPOULTRY announced.
According to a research summary by Machtinger, controlling house flies (Musca domestica) poses a significant challenge to poultry producers, especially those involved in managing layer facilities. Egg production occurs in facilities where the accumulation of manure in an enclosed space creates the perfect development habitat for fostering large numbers of flies, she said.
Historically, pest flies have been controlled with chemical insecticides, Machtinger noted, but regulatory restrictions, house fly resistance to current active ingredients in commercial pesticides and the lack of options labeled for pest control in poultry facilities make management of house fly populations difficult.
To control house flies, the poultry industry spends an estimated $20 million annually on pesticides alone, she reported, explaining that this estimate does not include the cost of animal loss due to house fly-vectored pathogens causing disease, the cost of labor for pesticide application or litigation that residents living near production facilities may bring due to increased fly numbers affecting their property values.
According to Machtinger, one potential option to control pest flies is integrating biological control agents into a layer facilities' integrated pest management program. Many natural antagonists of the house fly are found within the environment of the manure pit. Augmentative releases of these antagonists and the introduction of pathogenic organisms can help lower house fly populations to manageable levels, she said.
The most promising of these biological control agents on a commercial level are parasitoid wasps and the entomopathogenic fungi B. bassiana, she noted. Parasitoid wasps are commercially available and commonly released into poultry systems as a form of biological control, but more research needs to be done to determine which species or combination thereof would be the most effective in different geographic locations, Machtinger said, adding that B. bassiana has been widely studied as a form of biological control for house flies in layer facilities as well but has not been widely adopted by the industry.
She said the three objectives of this research project were: (1) to collect new fungal isolates from flies in poultry facilities and screen them to identify strains with fast kill times, (2) to test the most promising strains and subject them to selection for further improvements in kill times and (3) to ensure their compatibility with the most important natural enemies of flies (three species of parasitic wasps and the beetle predator Carcinops pumilio).
Objective 1 results included the collection of five new isolates of B. bassiana that had mean survival times under eight days -- an improvement from currently marketed B. bassiana products, Machtinger reported.
For objective 2, the researchers identified which strain was consistently the most virulent and produced the highest numbers of conidia on cadavers in fly-to-fly passages. Selection for faster-killing strains shortened the average time until death by three days, from 7.6 to 4.7 days, after nine generations of selection, she said.
For objective 3, Spalangia endius was the most resilient to the B. bassiana applications, whereas Spalangia cameroni and Muscidifurax raptor had decreased survival when B. bassiana was applied, Machtinger said.
Overall, the B. bassiana strains isolated from house flies killed greater numbers of flies than the negative control, she explained, while in parasitoids, all strains had a more limited effect than was observed in the house flies, except for in S. endius, in which there was no effect.
Machtinger concluded that the susceptibility of these house flies to the treatments and the lack thereof in all parasitoid species is a good indicator of the usefulness of field collected strains of B. bassiana and their use as a biological control tool. Given that the strains each demonstrated different traits in their infection of house flies, further research should be done to observe the extent of each of these traits and if they could be useful for biological control, she added.