Dispersal of Stable Flies:
Phenology of Dispersing Flies
Stable flies are a major constraint to cattle production in the Midwest; they are also a significant nuisance pest of humans and other domestic animals. Overwhelming numbers of adults have frequently been encountered hundreds of kilometers from the closest site where larvae could have developed. Our research is intended to create fundamental understanding of the mechanisms of stable fly dispersal.
During June 1996, we sampled stable flies from resting sites, in the surface layer of the atmosphere, and high in the planetary boundary layer. Thousands of flies were collected. We determined the sex and mated status for a large subsample during the field program and have recently completed the grading to determine their chronological and physiological ages.
Flies were collect at locations proximal and distal to feedlots on the Kansas State University Agricultural Extension and Research Station in Garden City, KS. We made approximately 75 truck collections with large nets (in a variety of configurations that included 1, 2, and/or 3 m heights) over a variety of routes that included circling the feedlots immediately outside the fence, loops around feedlots at a distance of 1 to 2 km, and collection runs over roads that were more than 5 km away from the nearest feedlot. We also deployed a large number of Alsynite (attractant) traps in a grid pattern around a large feedlot and at sites along country roads among wheat fields between 3 to 10 km from the nearest feedlot. Finally, we deployed a net from a remotely controlled aircraft that flew at a variety of altitudes between 5 and 50 m above the feedlots. Air temperature and humidity, wind speed and direction, air pressure, soil temperature, solar radiation, and precipitation were measured and averaged or totaled over half hour intervals at the Agricultural Station throughout the two-week study period. These devices may all be seen on the world wide web from last year's report.
During the daylight hours, flies often moved from the feedlots to nearby resting sites on fences and other structures, on plants in corn and wheat fields, and on the lower branches of trees and bushes. During these trips the flies flew within their flight boundary layer at altitudes less than 3 m. Flies were caught in the truck trap nets at the 1, 2, and 3 m levels at a ratio of approximately 25:4:1. Despite numerous airplane sorties, we were unable to catch a single fly in the planetary boundary layer above their flight boundary layer. Many aerial samples were obtained above the feedlots during early morning and evening hours while flies were moving within their flight boundary layer from the feedlots to resting sites in nearby fields. Even when winds were light and the airplane was able to sample the atmosphere 3 m above the backs of the cattle (4-5 m altitude), we were unable to capture flies with the aircraft mounted net.
We collected flies from the distal traps (3 - 10 km away from the nearest feedlots) each day. On some days there would be very few or no flies in the distal traps while on other days there would be as many as 200 flies in a single trap and very few in the others. We did not have a day when flies were abundant in more than one or two of the distal traps. Thunderstorms with updrafts that might carry flies long distances and deposit them in high concentrations far from feedlots were not present in the Garden City area during some of the 24 hr periods when flies were found in great abundance in the distal traps. For this reason, we suspect that stable flies are traveling long distances within their flight boundary layer. We have yet to determine a wind speed above which the flights are primarily downwind.
Our project was designed to determine the physiological parameters of flies that were captured at points distal from blood-meal sources, and in addition to vertical sampling, we chose stationary ground sites that were as close as 5 m to a cattle feed lot, and as far as 3-8 km from the nearest horse or cow operation. The mobile ground traps were operated in a variety of trajectories. One (Central) kept the vehicle within 5 and 50 m of the feedlot at the Kansas State University Southwest Research and Extension Center for 7.5 minute periods, another (Peripheral) placed the traps within 100 to 200 m of the station for a similar time period. This trap run did come within 50-75 m of several small livestock facilities. The final trajectory (Far) was a series of farm roads that were 3-8 km from known livestock operations. Sex, blood-fed status, nectar feeding status, physiological age and chronological age were determined for more than 500 captured flies, while subsets of these parameters as well as blood-meal source (host-species) have either been determined or are in progress for about 1500.
Statistically significant differences exist among populations captured by the techniques outlined above. The initial population aged markedly (P<0.01) during the first week of our study, though these results were probably diluted by continual recruitment, and broke down in week 2. In confirmation of previous work, we found that the flies attracted to our stationary traps were physiologically younger (P<<0.01) than flies captured in other ways. These flies were also chronologically younger, as well. A comparisons of chronological and physiological ages of flies caught by mobile trap distal to and those caught proximal to livestock, revealed that distal flies were physiologically younger, but chronologically older (P<<0.01). Flies caught in the central trap runs, however, were both chronologically and physiologically older than those captured on the peripheral routes. Stable flies are posited to travel long distances from livestock facilities in association with weather fronts. These data can be used to support movement of fairly long distances at levels of 3 m or less.
The low numbers of flies caught during the Far runs is in contrast to the large numbers collected on the stationary traps used in these distal areas (frequently collected several hundred flies on a single trap in a single day). Often stable fly numbers were so high at these traps that workers were more concerned with swatting flies than collecting them from the trap panels. In a similar manner, large numbers of flies suddenly appear in coastal recreation areas dozens (and in some locations 100s) of km from livestock facilities, where they bite bathers driving them from beaches. Long-distance dispersal of stable flies to recreational areas is a notable phenomena of significant economic importance both on beaches along the Gulf Coast of Florida and the Great Lakes. Our research team is developing a new program aimed at obtaining concurrent measurements of wind fields (radar) and insect concentrations (aircraft samples) within the lowest 3 km of the atmosphere coupled with NWS data on large-scale weather systems to allow evaluation of the roles played by lake breezes, convective storms, and weather fronts in concentrating flies along the shores of the Great Lakes. We believe that the knowledge gained during this study will provide the basis for developing and implementing stable fly management strategies. Further, it will provide a powerful tool for forecasting levels of stable fly nuisance at Great Lake beaches.
This page was constructed by Gail Kampmeier at gkamp[at]uiuc.edu
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