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United States Department of Agriculture

Agricultural Research Service

Research Project: ORIGIN, DEVELOPMENT AND POPULATION GENETICS OF STABLE FLIES AFFECTING PASTURED AND CONFINED LIVESTOCK
2010 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.


3.Progress Report
This is the final report for the project 5440-32000-008-00D which terminated in January 2010. Substantial results were realized over the 5 years of this project. Stable fly populations in eastern Nebraska were found to be bimodal with peaks in early and late summer. Population peaks were dependent upon the temperature 0 –2 weeks earlier and precipitation 3-6 weeks earlier. A model capable of predicting population peaks 2-4 weeks before hand was developed. Sites where large round bales of hay were fed to the cattle during the winter were identified as the primary sources of early summer stable flies. However, those sites were not responsible for the late summer stable fly populations. A single hay feeding site can produce 500,000 to more than 1,000,000 stable flies and producers frequently have several feeding sites in each pasture. Interestingly, house flies were not observed developing in hay feeding sites. Stable fly larvae in the hay feeding sites prefer to develop in moist, 40-65% water, basic, pH 8-9.5 substrates. Several species of parasitic wasps were found to be parasitizing stable flies in these sites. Mark-recapture studies found that half of the stable flies did not disperse beyond 1.6 km (1 mile) from where they developed and only 5% dispersed beyond 5.1 km (3.2 miles) indicating that developmental sites within a 2-3 mile radius of a premise will need to be incorporated into control programs. Assays to detect sugar and blood in adult stable flies were developed to assess adult feeding behavior. Sugar feeding rates, 10-15%, were higher than previously documented. The Hemoccult assay revealed that about 45% of field collected stable flies had previously blood fed. Dissecting the flies and visually scoring for blood in the gut, the technique normally used to evaluate if stable flies had blood fed, was positive for fewer than 1% of the same flies. Analysis of genetic variation of stable fly populations from across the US revealed very low levels of differentiation indicating relatively free dispersal and gene flow among populations. The efficacy of several fly traps was evaluated and as a result, a new trap, the Bite Free Stable Fly trap was commercialized. The economic impact of stable flies on cattle production in the US was estimated to be greater than $2 billion per year with a dynamic and explicit model developed as part of this project. Investigations on ways to reduce stable fly development in hay feeding sites and to control adult stable flies were initiated at the end of this project and will be the primary goals for our next 5 year project 5440-32000-009-00D Development of Tools for Integrated Pest Management Of Stable Flies.


4.Accomplishments
1. Characterized the seasonal and spatial dynamics of stable flies developing in winter hay feeding sites relative to adult stable fly populations. Adult stable fly populations begin to increase in the spring several weeks before flies begin to emerge from the hay feeding sites indicating that very early season flies are originating elsewhere. Peak emergence from the hay feeding sites correlates with the primary peak in adult fly populations observed in mid to late June indicating that hay feeding sites are primary contributors to that population. Stable fly emergence from hay feeding sites drops to very low levels in mid July indicating that late season stable fly populations are developing in other habitats. Stable flies emerging from hay feeding sites disperse a median distance of 1.6 km and only 5% disperse beyond 5.1 km. Control programs will need to address larval developmental sites within 3-5 km to effectively reduce adult stable fly populations.

2. Developed assays to determine the feeding status of adult stable flies and characterizing the ubiquity of sugar feeding. Assays based upon proprietary Hemoccult test strips and imipramine hydrochloride (IPH) were developed to detect remnants of blood in flies that had previously blood-fed. The tests are sensitive up to 8 days after blood feeding whereas visual detection of blood in the flies gut is possible only up to 24 hours after blood feeding. A cold anthrone test was developed to detect sugar in flies that have fed upon nectar. This test is sensitive for about 3 days after feeding. A survey of wild flies collected on alsynite sticky traps indicated that about 15% had fed on sugar and less than 5% had fed on blood.

3. The genetic characterization of US stable fly populations revealing high levels of gene flow. Variation in microsatellite loci and mitochondrial DNA sequences were analyzed in stable flies from 9 populations including New York, California, Florida, Nebraska, and Minnesota. Variation in mitochondrial COI sequences was low and measures of genetic differentiation indicated high levels of gene flow among populations.

4. Identifying the utility of a trap being marketed for other uses to trap large numbers of stable flies. A trap originally designed to be a replaceable insert for an ultraviolet light trap was compared with several traps traditionally used for sampling stable fly populations. The test trap collected more stable flies than did any of the other traps. In response to this work, the manufacturer relabeled the trap as the Bite Free stable fly trap and it is now the only commercially available trap for the control of stable flies.

5. Development of a dynamic and explicit model to predict the economic impact of stable flies on cattle production. A model using current commodity prices and cattle inventories with response functions developed from published studies was developed to estimate the economic impact of stable flies on dairy, cow / calf, stocker, and feeder cattle. Using an estimate of 5 stable flies per let for 3 months of the year for a US average, the estimated impact of stable flies on cattle production is $2 billion per year. This estimate is nearly 3-times higher than previous estimates. The model is dynamic in that all variables can be modified by the user and results can be broken down by state.

6. Identified catnip oil to be an effective repellant for stable flies. ARS scientists in Lincoln, NE, discovered a 15% oil-based catnip oil formulation effectively repelled stable flies on test cattle for 6-7 hours. Wax based pellet and spray formulations of catnip oil provided area repellency of stable flies for up to 24 hours and inhibited stable fly egg laying on treated substrates.


Review Publications
Berkebile, D.R., Weinhold, A.P., Taylor, D.B. 2009. A New Method for Collecting Clean Stable Fly (Diptera: Muscidae) Pupae of Known Age. Southwestern Entomologist. (34):469-476.

Zhu, J.J., Polavarapu, S., Park, K., Garvey, C., Mahr, D.L., Nojima, S., Roelofs, W., Baker, T.C. 2009. Reidentification of pheromone composition of Sparganothis sulfureana (Clemens) and evidence of geographic variation in male responses from two US states. Journal of Asia-Pacific Entomology. 12:247-252.

Last Modified: 11/26/2014
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