2007 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.
Various types of "fingerprints" can be used to distinguish populations and determine the origin of migrant stable flies. X-ray fluorescence detected the concentration of 27 elements in stable flies from 6 geographic areas: California, Florida (2), Georgia, Kansas and Texas; 13 elements showed significantly different levels between 2 or more of the 6 populations. Additional specimens need to be analyzed.
Stable flies may acquire pollen while feeding on nectar. Stable flies were collected from 1 urban and 5 rural locations throughout the fly season. The presence of pollen on the body and in the digestive tract is being analyzed by a pollen specialist; pollen identification will provide insight into the feeding habits and origin of the stable fly.
Winter hay feeding sites have been identified as an important source of stable flies in early summer. Sites were sampled weekly for the presence of immature stable flies throughout the season. The material was also sampled to determine moisture content, pH, conductivity and ammonia levels to characterize larval development sites. Stable flies prefer to develop in moist (40-65%) and basic (pH 8-9.5) materials. Additional materials have been collected for analysis with gas chromatography-mass spectrometry.
Loafing areas, wet areas around watering tanks, and other areas where cattle congregate were sampled in early June, when development is normally at a peak. No stable fly larvae were found in any of these materials.
Emergence traps were used to monitor adults at winter hay feeding sites. Larval migration into the area covered by the trap was eliminated by inserting a sheet metal barrier into the ground. The traps were placed in the field in the spring. Data from the emergence traps will help us to determine the contribution of the hay feeding sites to stable fly development and provide additional information about stable fly biology.
Parasitic wasps were monitored at a feedlot and at two winter hay feeding sites using fresh house fly pupae and frozen stable fly pupae. Pupae were placed around the perimeter of each site each week. After one week in the field, the pupae were returned to the laboratory to allow any parasites to emerge.
A pile of cattle feedlot manure and a pile of corn silage were made in the late summer/early fall. These piles were exposed to late season stable fly populations. Large outdoor insect cages were used to cover the piles before the appearance of spring stable fly populations. Ground piled silage has potential as a stable fly overwintering site.
Larval developmental times were extended to over 2 months by exposing stable flies in standard laboratory rearing medium to 55ºF, when lowered to 50ºF no stable fly larvae survived. To survive over winter, temperature and/or photoperiod cues may be required to re-program the stable fly to survive lower temperatures extending the developmental period to the required 3-4 months of the winter season.
The mitochondrial COI gene has been sequenced in populations from Florida, New York, California, Minnesota, Nebraska and Kansas. Sequence variation levels are very low, to date no differentiation of populations can be made.
Sugar and Blood Feeding in Adult Stable Flies
Sugar and blood feeding in stable flies was assessed by using the Anthrone technique to detect sugars in wild stable flies collected from sticky alsynite traps from six “rural” and six “urban” locations for two 24 hour periods per week from May – October 2006; 7,423 were examined for sugar and blood feeding (<24 flies / trap / day). Sugar was detected in 22% of the urban flies and 8% of the rural flies. Blood was detected in 14% of the flies, both rural and urban; 13% of the female flies and 12% of the male flies had sugar fed while 16% of the females and 13% of the males had blood fed. Sugar feeding was highest in the spring and then dropped off during the late summer and fall but blood feeding was relatively constant throughout the season. This shows the importance of sugar feeding to the survival of the stable fly. This project addresses Component 3 (Biology, Physiology and Vector-Pathogen Interaction) of NP 104,”Veterinary, Medical and Urban Entomology”.
Spatial Distribution of Stable Fly Populations
The spatial distribution of a stable fly population was assessed with a grid of 25 Alsynite-adhesive traps distributed in a 16 square mile diversified agricultural environment in southeastern Nebraska for three years. Collections among trap locations did not vary synchronously over time; rather, individual trap collections rose and fell relatively independent of collections at other trap locations. Correlation of temporal collection levels between traps was related to the distance between those traps. Stable fly populations were highest near confined animal operations, but the effect was limited to about 0.5 mile from the facility. Variation in overall amplitude and seasonal distribution of stable fly populations as measured by Alsynite adhesive traps indicates that multiple traps dispersed across the area of interest are needed to accurately assess stable fly populations as individual traps can miss significant population changes as close as 0.5 mile away. This project addresses Component 2 (Detection and Surveillance Technology) of NP 104,”Veterinary, Medical and Urban Entomology”.
Genetic Variation of Wolbachia
In conjunction with Ag-Canada, genetic variation in Wolbachia (a bacterium associated with the reproductive organs of many insects) in Spalangia spp. (parasitic wasps of stable fly) was examined. Some species of wasp were associated with distinct Wolbachia. One species of wasp was associated with several distinct Wolbachia typically in the same individual. This project addresses Component 3 (Biology, Physiology and Vector-Pathogen Interaction) of NP 104,”Veterinary, Medical and Urban Entomology”.
5.Significant Activities that Support Special Target Populations
|Number of non-peer reviewed presentations and proceedings||1|
Berkebile, D.R., Sagel, A., Skoda, S.R., Foster, J.E. 2006. Laboratory environment effects on the reproduction and mortality of adult Screwworm (Diptera: Calliphoridae). Neotropical Entomology. 35(6):781-786.
Carlson, D.A., Berkebile, D.R., Skoda, S.R., Mihok, S. 2007. Candidate sex pheromones of the new world screwworm Cochliomyia hominivorax. Medical and Veterinary Entomology. 21(1): 93-96.
Taylor, D.B., Berkebile, D.R., Scholl, P.J. 2007. Stable fly population dynamics in Eastern Nebraska in relation to climatic variables. Journal of Medical Entomology. 44(5):765-771. Available: http://titania.esa.catchword.org/vl=317740/cl=21/nw=1/rpsv/cw/esa/00222585/v44n5/s6/p765