Flies Impacting Livestock, Poultry and Food Safety

NON-TECHNICAL SUMMARY: This project will study population dynamics of stable flies and houseflies and factors that regulate their populations. Because (a) stable flies have become the number one pest of pastured livestock, (b) we have limited knowledge of these flies in these settings, and (c) there is no effective method for their control, efforts will be aimed at providing information that will direct research on how to manage their populations. Thus, we will direct research efforts to clarify the important question on whether the early spring founding populations of stable flies in the Midwest U.S.A. are from flies that over wintered locally, flies that migrated from southern sources, or flies from both sources. Answering this question will provide guidance into managing their populations by chemical (insecticides), cultural (reducing larval habitats), biological (parasitic insects, nematodes), and mechanical (traps) control methods. Antibiotic resistance of food borne and other clinical isolates has become a serious problem because of the limited number of effective antibiotics available for treatment of human bacterial infections. Due to their developmental habitats, mode of feeding, unrestricted movement, and attraction to residential areas, houseflies likely play an important role in the ecology and dissemination of virulent and antibiotic resistant bacteria in the environment. The vector potential of house flies and their capacity to contaminate ready to eat food with enterococci and associated antibiotic resistance and virulence factors will be assessed.

<P>APPROACH: Seasonal dynamics of stable flies and house flies developing at winter hay feeding sites will be evaluated by core sampling and emergence traps; core samples will be held in the lab for fly emergence from the different zones of the feeding sites and the subsequent characterization of these zones. The characterization of these larval habitats will be used to focus efforts on devising new control strategies. The contribution of migration and over wintering to the origin of stable flies composing new populations in early spring will be studied by monitoring the dynamics of both of these biological phenomena. For over wintering, cattle manure and various cattle feed will be mounded in the fall and inoculated with stable fly larvae (wild and lab reared) once a week for 6 weeks during Nov. thru Dec. Some mounds will be fitted with temperature probes to monitor the horizontal and vertical temperature profiles of the various media mounds. Pyramid emergence traps will be placed over the mounds during February and fly emergence monitored through May. For migration studies, alsynite cylinder traps will be used to monitor stable fly populations in southern U.S. livestock operations (as putative sources of migrating flies) and daily along putative routes of migration with the northward masses of warm air as cold fronts approach the U.S. Midwest. Physiological age and blood feeding status of flies collected in both southern and Midwest areas will be compared; elemental rare earth concentration in heads of flies from both areas will be analyzed by neutron activation analysis and compared. Collected flies will be provided to other participating units for conducting mitochondrial and microsatellite genetic analysis. Adult houseflies (100-200) will be collected from animal production facilities, screened for E. faecalis, E. faecium and used in food contamination bioassays. Ready to eat food (RTEF) (hamburger, vegetable salad, and carrot cake) from fast food restaurants will be first screened for enterococcal contamination level in winter and summer. In summer, RTEF will be exposed to various numbers of flies (1, 5, 10, 20, 40) for various time periods (0.5, 1, 3, and 24 hrs). Before and after each exposure, 20 randomly selected flies will be individually screened for enterococci. After each bioassay, the food sample will be screened for enterococci. Phenotypic and genotypic approaches will be undertaken to quantify, identify and characterize (antibiotic resistance and virulence) the enterococcus population. Survival of stable fly larvae in the hay manure medium after addition of chemicals for modifying this mediums pH and osmolality will be evaluated in the lab and field; including lime, sulfur and ash. Insecticides currently registered as oral larvicides but limited as spray treatment of hay feeding sites because of the medias crust, will be evaluated after modifications to site and method of application. The efficacy of treated targets (insecticide-impregnated) in reducing populations of stable flies will be assessed in small pastures and Greyhound kennels (where stable flies do not develop but are serious pests). <P>

PROGRESS: 2007/01 TO 2007/12<Br>
OUTPUTS: Control of populations of stable flies in pastures by managing their development at the winter feeding grounds of hay in round bales has been ineffective. Cultural control by managing the hay-manure larval medium does not appear to be popular among producers as they have other husbandry tasks considered to be of higher priority during the winter. Chemical control is ineffective due to poor residual activity and penetration of the hay-manure material by applied larvicides. The efficacy of diflubenzuron (Dimilin 2L), a chitin inhibitor, against stable fly larvae developing in the hay-manure medium at these sites was evaluated during the spring and summer by applying the chemical as a drench; emergence traps over treated and control sites assessed results. Diflubenzuron at the rate of 0.5 g a.i./meter square maintained a 83.7% control for 19 days, whereas a higher dose of 1.0 g a.i./meter square maintained a 73.6% control for 21 days. This discrepancy in results is probably due to the complex nature of the hay-manure medium. Two hypotheses have been proposed to explain the appearance of stable flies in early spring in the Midwest USA: the overwintering of immatures in silage/manure mounds vs the migration of adults riding southerly winds ahead of approaching synoptic cold fronts. Answer to this question is essential to developing managing programs for the early populations that will eventually become economically important. To evaluate the possible dynamics of overwintering in silage/manure mounds, a study was initiated by building mounds of silage, manure, and manure mixed with two levels of hay. Temperature at various depth levels of the mounded materials was recorded and 1st instar stable fly larvae introduced, with plans for adult emergence recording. <Br>PARTICIPANTS: A. Broce, L. Zurek. Kansas State University, Department of Entomology, Manhattan, Kans. <Br>TARGET AUDIENCES: Livestock production units, both confined and pasture operations.
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IMPACT: 2007/01 TO 2007/12 <Br>
Although the chitin inhibitor diflubenzuron gave 74 - 84% control of developing stable flies in hay-manure media at hay feeding sites, this level of control is promising, specially if it can be combined with other control methods, such as cultural. Given that it has been demonstrated that cultural control offers the best control at these sites, but producers have hardly embraced this technique, a chemical control component might be more acceptable and applied by producers. Temperature of mounded materials was monitored and compared to that of the ambient air. Temperature at the different depths differed significantly, with silage offering the most insulation whereas pure manure offered the lowest insulation. By the middle of December 2007, temperatures of manure, and manure/hay mixtures had already reached to that of soil, indicating the mounds were frozen throughout, thus offering little insulation value to larvae. These results might be indicative of an unexpected and not accounted for factor: The compaction of mounded materials. These findings will be used as basis for a similar study in 2008 which will take into consideration factors identified as important during this study.