2009 Annual Report
1a.Objectives (from AD-416)
To gain a better understanding of stable fly population dynamics by elucidating their genetic structure throughout North America. To identify and characterize stable fly larval developmental sites and correlate larval production with adult population dynamics in relation to season, climatic variables and cultural practices. To determine the relative contributions of overwintering and migration to early season, colonizing, stable fly populations.
1b.Approach (from AD-416)
Methodologies to achieve the objectives include: Development of genetic markers and application of population genetic analyses to understand the structure of stable fly populations and the roles of migration and genetic drift in maintaining the observed structure. Surveys will be conducted to identify stable fly larval developmental sites. The production and phenology of developmental sites will be determined. Production will be correlated with adult populations to identify primary contributors to pest fly populations. Surveys will be conducted to identify stable fly overwintering habitats. Overwintering habitats will be characterized. Artificial overwintering habitats will be developed to study the environmental limits of overwintering stable flies.
Population genetics of stable flies: The microsatellites of five populations of stable fly have been analyzed. We are in the process of analyzing 3-4 more populations which have been obtained this summer. The preliminary results show very little genetic differentiation among populations.
Larval Habitat. Weekly core samples were taken at 27 locations in a winter hay feeding site and examined for the presence of immature stable flies. After removal of the core a hardware cloth cylinder filled with laboratory stable fly rearing media was place in the hole to attract and trap additional stable fly larvae. This is an additional method by which stable fly populations can be evaluated in their developmental habitats. Two similar habitats were monitored for stable fly production with 27 emergence traps. The traps were moved to new locations within the site every 5 weeks and the number of emerging adult flies was monitored weekly. Larval sampling allows us to monitor the stable fly population before they become a pest and the emergence traps provides information about adult production by the site. Pans of alfalfa, oats and standard laboratory stable fly medium were placed in the field to test for their ability to attract ovipositing female stable flies and support larval development. One pan of each material was placed in 3 pastures and a feedlot. The pans were returned to the laboratory to recover the developing stable flies and replaced with pans of fresh media every two weeks.
Laboratory Larval Media Studies: The study of the effect of varying levels of food preservatives on stable fly survival was continued. The addition of phosphoric acid, methyl paraben, citric acid and nitrite promotes mold development. A reduction in stable fly survival was associated when methyl paraben, citric acid and nitrite were used but not phosphoric acid. This may indicate that the different compounds may promote the growth of different molds that affect stable fly survival differently. Sorbic acid reduces mold growth and at low rates leads to an increase in stable fly survival but at higher rates other microorganisms are affected and a decrease in stable fly survival occurs.
Pupal parasites. Small nylon screen bags containing 50 stable fly or house fly pupae were placed weekly at 10 locations at a feedlot and 3 winter hay feeding sites. The pupae remained in the field for 7 days. The pupae were then returned to the laboratory. Fly emergence and the emergence of the parasites were monitored for 6 weeks. This will provide information about variation of parasite between habitats and throughout the season.
Solarization of Stable Fly Larval Habitat. Three winter hay feeding sites were used to test the use of plastic covering to increase the temperature in stable fly larval habitat. Half of each site was covered and the other half was uncovered. Temperature was monitored at two depths for each treatment at each site. The plastic raised the temperature by 10-15° C at 5 cm and 5°C at 15 cm. This increase in temperature did not reduce stable fly survival.
Catnip oil was found to reduce feeding by stable flies 96% and house flies 79%in a laboratory bioassay. As a spatial repellant, catnip oil reduced stable fly oviposition by 98%. Catnip oil was toxic to stable flies as well, with a knock-down time of 6 minutes and kill time of 16 minutes. Lethal concentration to kill 90% of the flies was 19.6 mg. A slow release formulation of 10% catnip oil showed 90% repellency in cattle feedlot trials. Toxicity tests revealed low oral and dermal toxicity for catnip oil. Compared to other EPA approved repellents, catnip oil appears to be the least toxic.
The use of food preservatives in stable fly larval diet has confirmed the importance of microorganisms to the survival of the stable fly. Methyl paraben, citric acid and nitrite promote mold growth that reduces stable fly survival, while phosphoric acid promotes mold growth but does not substantially affect survival. Sorbic acid effectively reduces mold development and at low levels is associated with an increase in stable fly survival. Sorbic acid at higher levels and acetic acid are effective preservatives that reduce other microbial growth and stop or slow fermentation and stable fly development. This work confirms the importance of microorganisms to stable fly development. Additional research is required to understand these relationships.
Akasaka, K., Carlson, D.A., Ohtaka, T., Ohrui, H., Mori, K., Berkebile, D.R. 2009. Determination of HPLC fluorescence analysis of the natural enantiomers of sex pheromones in the New World screwworm fly, Cochliomyia hominivorax. Medical and Veterinary Entomology.23:126-130.
Zhu, J.J., Zeng, X., Berkebile, D.R., Du, H., Tong, Y., Qian, K. 2009. Efficacy and Safety of Catnip (Nepeta cataria) as a Novel Filth Fly Repellent. Medical and Veterinary Entomology. 23:209-216.