Abstracts of 1998 Joint Session on Weather Data Requirements for Integrated Pest Management 23rd Conference On Agricultural & Forest Meteorology 13th Conference On Biometeorology & Aerobiology Second Urban Environment Symposium 3.1 DISPERSAL OVER SHORT DISTANCES (THAT IS, LESS THAN 5.0 KM) BY SMALL INSECTS David N. Byrne, Univ. of Arizona, Tucson, AZ Comparatively little is known about migration and dispersal by small (less than 100 micrograms) insects moving short distances (less than 5.0 km) across agricultural landscapes. This lack of information is being corrected as more scientists address these phenomena. In our laboratory, we have been studying dispersal by sweet potato whiteflies, Bemisia tabaci, as they move from summer crops, such as cotton, into fall vegetables. Our initial conclusions were that these insects were not capable of sustained flight. Reasons included; they were members of a taxon that is almost exclusively associated with perennial hosts in the tropics, they were likely too small (ca. 45 micrograms) to have large quantities of flight fuels, and high surface to volume ratios would result in rapid desiccation in the Southwest. Early studies obtained using a flight chamber proved us wrong on several counts. In these laboratory studies, ca. 6% of the population flew for greater than 30 min. Some sustained flight for greater than 2 hr. These insects seemed to be conforming to classic definitions of insect migration, i.e., during their flight they initially ignored vegetative cues in favor of skylight cues, but eventually focused on cues mimicking plants. Mark-recapture field studies demonstrated that the majority of the population dispersed at least 2.2 km during a 3 hr-period. Further studies have shown that there is an optimal age for flight by Bemisia tabaci. Flight activity was demonstrated to be associated with changes in the flight musculature and mitochondria associated with indirect flight muscles. Other research characterized the vertical component of their dispersal. We demonstrated that aerial density of Bemisia tabaci decreases with height above ground. Aerial whitefly density also decreased with distance from the point of take-off. We captured marked whiteflies at 7.3 m above the ground in traps at the edge of the source field, indicating a rapid rate of ascent for some individuals. Females trapped in this study were also used to determine mean egg load for insects captured at four heights (0 to 7.3 m). A highly significant negative correlation was found between height trapped and egg load, indicating that there may be a trade-off in B. tabaci between production of eggs and the ability to disperse. Recent studies have been undertaken concerning whitefly parasitoid dispersal. The dispersal abilities of Eretmocerus eremicus have been examined in the vertical flight chamber to determine its dispersal potential. It is our plan to eventually compare their flight behavior to that of B. tabaci. Preliminary results clearly indicate that there is a statistical difference in flight duration between males (1 min av., 10 min. maximum) and females (19 min av., 93 min. maximum). 3.2 THE INFLUENCE OF WEATHER ON INTERFIELD AND REGIONAL MOVEMENT OF WESTERN CORN ROOTWORM Scott A. Isard, Univ. of Illinois, Urbana, IL; and J. L. Spencer, E. Levine, and D. W. Onstad Since 1993, western corn rootworm (WCR) beetle, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), the most serious insect pest of corn, have altered their movement behavior in east-central Illinois to lay eggs in soybean fields, reducing the effectiveness of crop rotation for WCR control. Now it appears that adult WCR have changed their behavior to feed on soybeans as well. On most days from late July to early September, WCR fly between corn and soybean fields to feed and lay eggs. Many of the questions relevant to the development of improved IPM for WCR require an understanding of the timing of WCR presence in soybean fields and the extent of the &amp;quot;problem area&amp;quot;. WCR movement into a soybean field is related to solar radiation, wind speed and direction, air temperature, and precipitation with consideration of biological factors that also influence flight. WCR flight activity and meteorological variables were measured above the canopy of an 1.64 ha soybean field in east-central Illinois between late July and early September, 1997. On 14 days, insect traps were sampled at 30-min intervals. The day-to-day variation in WCR movement was large. Overall, 61% of the WCR collected were female, although this proportion rose throughout the growing season. A diel periodicity in WCR immigration to and emigration from the soybean field was observed on days conducive to beetle flight. From 601 to 1000 solar time, immigration of WCR to the soybean field exceeded emigration. Flight activity peaked between 1001 and 1200, with emigration exceeding immigration. The abundance of WCR in the field reached a minimum at this time. By 1600, more WCR were again flying into the soybean field than leaving, and WCR abundance in the soybean field reached a maximum just before sunset. WCR were not caught in the malaise traps between sunset and sunrise. Interfield movement of WCR occur over a wide range of solar radiation loads, air temperatures, and wind speeds. Darkness, air temperatures below 15 °C or above 31 °C, and wind speeds in excess of 2.0 m/s-1 prohibit aerial movement of WCR. Within these limits, atmospheric factors had only little influence on the biologically-driven seasonal and daily temporal patterns of WCR flight activity. Atmospheric conditions were conducive to WCR flight during 62% of the 10-min measurement intervals during the growing season when biological factors enabled WCR to move among fields. Interfield WCR movement was substantially reduced by weather conditions throughout entire diurnal periods during about one-third of the days when female WCR beetles were abundant at the study site in 1997. Region-wide sampling and modeling reveal a strong influence of convective storms on long-distance WCR dispersal. The new strain of WCR has moved from east-central Illinois eastward through Indiana to Ohio and Michigan, but is spreading only slowly to the west. 3.3 USING PHENOLOGY TO DETECT DISPERSAL OF STABLE FLIES IN WESTERN KANSAS Carl J. Jones, Univ. of Illinois, Urbana, IL, ; and J. A. Hogsette, S. A. Isard, Y. -J Guo, Greene, and A. B. Broce The stable fly, Stomoxys calcitrans, is a cosmopolitan pest of animals and humans found throughout most terrestrial habits on earth. Genetic studies of this insect indicate that populations in the United States may be nearly panmictic. Although larval development sites for this insect are primarily restricted to livestock operations, hence the name stable fly, large numbers of flies often appear in residential and recreational areas far from these locations. Frequent inundations of ocean beaches and lakeshore areas, known for more than 70 years in the United States, by this biting fly have had negative economic impacts on local tourism. One study, using self-marking technology, documented movement of flies to a beach in Florida from an agricultural region 225 kilometers to the northwest. However, neither the biological cause of movement nor the relationship of that cause to the atmospheric motion systems that help transport stable flies long-distances have been clearly defined. The stable fly presents an excellent target for aerobiological studies. Large, the approximate size of a house fly, and relatively easy to find and identify because of its prominent beak-like mouthparts, the primary food sources for adult flies are a variety of large mammals. Because the stable fly is a serious pest of humans and animals, causing both economic damage and disease transmission, its physiology and behavior have attracted substantial interest from scientists for many years. There are two techniques that can be employed to assess stable fly age. The first uses the condition of a female fly's ovaries to estimate the number of blood-meals she has taken. From that data we can estimate the number of days during which she has been in the vicinity of appropriate food sources. The second uses the amount of pterin in the eye of either sex to estimate the number of days that have passed since adult fly emergence. To test the utility of age-grading techniques for studying the aerial movement of a stable fly population, we made collections of a large number of stable flies various distances from isolated feedlots in southwestern Kansas during 1996. Flies were collected from mid-June through the end of June, using truck mounted mobile insect traps and stationary insect traps. Stable flies were collected as high as three meters in the air. A drone aircraft was unsuccessful at collecting stable flies at higher altitudes, although a few other arthropods were collected during these aerial runs. Using the age-grading techniques described above, we were able to statistically differentiate among the mean ages of the flies collected on the feedlot, adjacent to the feedlot, and three or more kilometers from known larval development sites or bloodmeals. In addition, we were able to determine phenological differences among flies that had dispersed and those that remained near the feedlots. 3.4 CORN EARWORM MIGRATION TRAJECTORIES IN THE LOWER RIO GRANDE VALLEY OBSERVED WITH AN INSECT MONITORING RADAR V A. Drake, Univ. of New South Wales, Canberra, A.C.T, Australia; and I. T. Harman, J. K. Westbrook, and W. W. Wolf The Lower Rio Grande Valley (LRGV) in Texas has an abundance of host crops that can support significant populations of corn earworm (Helicoverpa zea). Adults migrate into the Valley in early March and the following generation emigrates in June. Favourable meteorological conditions can transport migrants over 400 km in one night. Field surveys and trapping are useful to establish identity and emergence trends, but provide little insight into population movements. ARS have used scanning, tracking and vertical-looking radars to study these migration flights over several seasons. In 1996, these radar studies were supplemented with a UNSW Insect Monitoring Radar (IMR). The IMR is vertical-pointing and combines a nutating beam with rotating linear polarisation. Special algorithms allow it to automatically measure characteristics of over-flying insects that simpler vertical-looking radars cannot determine. As well as insect track, heading, and speed, the IMR can be used to estimate size, body shape and wingbeat frequency. These additional parameters improve the IMR's ability to reliably classify over-flying targets, thus providing an improved capability for monitoring population movements. The IMR was operated from Moore Air Base near Edinburg in the LRGV in March and June of 1996. ARS deployed a network of scanning, tracking and vertical-looking radars in and north of the Valley to monitor migration from the LRGV and sources from within Mexico. Each campaign allowed the IMR to compile vertical profiles of migration intensity, speed, direction, heading, and wing-beat frequencies. All radars operated when H. zea were the predominant species emerging. An overview of data obtained by the IMR during these exercises will be presented. Comparisons and contrasts with participating ARS entomological radars will be made. The utility of the IMR for research and operational applications in this region will also be discussed. 3.5 MIGRATORY FLIGHTS OF BOLLWORMS, HELICOVERPA ZEA (BODDIE), INDICATED BY DOPPLER WEATHER RADAR John K. Westbrook, USDA, College Station, TX; and W. W. Wolf Reflectivity from flying organisms including the adult bollworm, Helicoverpa zea (Boddie), is often detected in clear-air mode by WSR-88D Doppler weather radars of the NEXRAD system. During migratory seasons in south-central Texas, reflectivity from these targets reached 5 to 30 dBZ, which exceeds the lower threshold for precipitation mode. Sequential reflectivity scans showed a rapid increase in reflectivity (i.e., aerial insect abundance) over the cropped land of the Lower Rio Grande Valley by 0.5 hours after sunset. The nightly pattern of maximum reflectivity displaced approximately downwind. Results show strong positive relationships between insect concentration measured by (X- band) entomological radar and WSR-88D reflectivity, and between wind velocity and doppler velocity. Considerations due to the WSR-88D beam geometry and characteristics of insect distribution will be discussed. 4.1 CHARACTERIZING AND FORECASTING THE AERIAL FLOW OF BIOTA BETWEEN THE SUBTROPICAL AND INTERIOR REGIONS OF NORTH AMERICA Stuart H. Gage, Michigan State Univ, East Lansing, MI; and S. A. Isard Organisms that utilize the atmosphere for translation from one geographic place to another may flow within atmospheric motion systems along routes that are mediated by physical and biological features of the earth's surface. The pathways and timing of the flow of biota are to a large degree regular, and thus the movement of organisms in the atmosphere is predictable. This paper attempts to characterize a strategy to quantify the flow of organisms in the atmosphere in central North America. Our objective is to provide a conceptual framework to assist others interested in studying the role that the atmosphere has on the movement of organisms ranging from viruses to waterfowl. The objective of the paper is to describe the biological and meteorological phenomenon that influences the flow of biota in the atmosphere by examining the processes from a regional perspective. In particular, we believe it is important to quantify the spatial and temporal scales at which the process of atmospheric and biological movement occurs. One of the drivers of biotic flow in the atmosphere tends to be the synchrony between biological and meteorological phenomena. The variance in this synchrony is crucial to understanding the timing and abundance of these flow patterns. The source of this variation in biological and meteorological features ranges from global scales to micro scales both in time and in space. We plan to illustrate the array of physical and biological features that operate at multiple scales by focusing on airflow patterns and biological patterns that are characteristic of the Central US. We will characterize the confluence of meteorological components including the dynamics of Rossby Waves, the mid-latitude cyclones and the influence of landscape features such as topography and how these interplay with vegetation organization. We will examine the phenological characteristics of vegetation at a regional scale, which play a significant role in the temporal synchrony of life stages of organisms that are prone to move long distances under the appropriate meteorological conditions. Such regional characterization of biological and meteorological systems requires a scheme for obtaining measurements of long range movement of organisms. We will examine the concept of establishing strategic sampling stations, following the example of the meteorologists who developed standards of measurement of meteorological variables long ago. We will suggest focusing on specific organisms representing the array of sizes and types that have been observed to move long distances, assisted by airflow. Finally, we will examine some of the techniques associated with the measurement of biota, the measurement of landscape characteristics and the means of analysis and communication of information about the findings. The regional assessment of the frequency and amount of movement by organisms is gaining in importance. Development of transgenic organisms, changing patterns of weather, the mobility of exotic species and our lack of understanding of the role movement of organisms in the dynamics of ecosystems are some of the reasons for undertaking development of a plan to assess organism movement. 4.2 FLIGHT ENERGETICS AND OPTIMIZATION STRATEGIES FOR LONG-DISTANCE INSECT MIGRANTS Robert Dudley, Univ. of Texas, Austin, TX The energetic costs of flight influence insect migration strategies for wind-assisted dispersal as well as for intentionally directed displacement within the flight boundary layer. Small insects being convectively dispersed must nonetheless maintain a forward airspeed and offset their body weight during flight, or alternatively must reduce their flight velocity so as to hover within a moving air volume. If the goal of dispersal is to maximize the horizontal distance travelled, then flight at the minimum power speed would maximize time aloft and thus the magnitude of wind-assisted displacement. By contrast, migration within the flight boundary layer likely occurs at the maximum range speed that optimizes horizontal coverage using powered flapping flight alone. No data are presently available that assess insect airspeeds (as distinct from groundspeeds) and associated rates of energetic expenditure during predominantly convective dispersal. Moreover, aerodynamic models that predict optimal airspeeds are seriously compromised if energy stores can be replenished during migration. For boundary layer migrants in particular, the fixed availability of endogenous reserves may be substantially augmented through nectar feeding or related strategies during long-distance flights. In such cases, the optimal flight speed for maximum migratory distance may vary substantially according to the instantaneous mass and energy balance. A diversity of energetic strategies may thus characterize both boundary layer migrants as well as predominantly wind-assisted migratory forms. 4.3 A FRAMEWORK FOR STANDARDIZING FLIGHT CHARACTERISTICS FOR SEPARATING BIOLOGY FROM METEOROLOGY IN LONG-RANGE INSECT TRANSPORT Gary L. Achtemeier, USDA Forest Service, Juliette, GA One of the most exciting questions raised by studies of long-range insect transport is "Once airborne, to what extent do insects contribute to their destination?" Radar studies showing layers of insects flying at or near the level of the low level jet and with peculiar orientation lend credence to the view that these biota are in some way participating in their migration. A simple modeling approach is hypothesized to separate biology from meteorology in long-range insect transport. Measurements of the thermal structure of the atmosphere through which insects are flying can be combined with terminal velocity and ascent rates for an ensemble of insects to model expected insect behavior. Departures from model predictions should be caused by higher-order meteorological phenomena and biology. Continued refinements of the model should isolate the biology of long-range transport, if any. 4.4 GRASSHOPPER MIGRATORY TENDENCY AS THRESHOLD TRAIT Jack W. Kent, Univ. of Texas, Austin, TX; and M. A. Rankin The North American migratory grasshopper Melanoplus sanguinipes (Fabricius) has engaged in spectacular outbreak swarms several times in the 20th century, and substantial numbers of individuals in many populations perform long-distance flights even in non-outbreak years. In the field, migratory flights typically begin under specific conditions of light, temperature, and windspeed that can be simulated in laboratory tethered-flight experiments. There is individual variation in migratory tendency, both within and between populations, that appears to have a substantial genetic basis; movements of grasshopper populations are therefore influenced by both environmental and internal cues. Previous work has found that (1) tethered-flight performance in the laboratory is correlated with migratory tendency in natural populations; and (2) tethered-flight performance is bimodally distributed, because individuals tend either to not fly (or fly for only a few minutes), or to fly for much longer than one hour. In the present work, we analyze migratory tendency as a threshold trait, using performance of 60 - 80 min of tethered-flight in at least one of three trials as diagnostic of a prospective migrant. In a laboratory population derived from a migratory Arizona population, heritability of migratory tendency is estimated to be in the range 0.3 - 0.5. In males, artificial selection on the frequency of flights 60 - 80 min in duration increases both the frequency and the mean duration of flights > 60 min. Previous work suggests that while carbohydrate is the principal fuel for short flights and flight initiation, lipid is the principal fuel for long-duration flight. Therefore, in this study we examine the correlated response of characters relating to lipid metabolism to artificial selection on migratory tendency. These characters include lipid reserves as percent of body mass, thoracic volume, relative size of thoracic lipid reserves, and amount of adipokinetic hormone (AKH) stored in the corpora cardiaca. 4.5 DEVELOPMENT OF A DATA ACQUISITION SYSTEM FOR LONG-TERM OUTDOOR RECORDING OF INSECT FLIGHT ACTIVITY USING A PHOTOSENSOR Aubrey Moore, Northern Marianas College, Saipan, Commonwealth of the Northern Mariana Islands Hardware consists of an upward-looking photosensor connected to a personal computer via the microphone jack of a 16-bit sound card. A custom-written Windows95 program monitors the voltage output from the sensor which is continually digitized by the sound card at a rate of 8000 samples per second or higher. Reflections and shadows of individual insects flying between the sun and the photosensor trigger the recording of transient signals which contain species-specific wingbeat waveforms that are typically rich in harmonics. Cepstrum analysis filters out low harmonic-content signals triggered by environmental noise. Waveforms passing through the filter are stored on disk with a time stamp so that they can be correlated with solar radiation, air temperature, speed, and direction monitored by an automated weather station. The system is designed to run unattended for weeks at a time. Analysis of flight activity data from long-term field tests of the system on the island of Saipan will be presented. [ back to 1998 NCR-148 Minutes ]
Last updated 1 June, 2007 This page was constructed by Gail Kampmeier at gkamp[at]uiuc.edu Please direct questions of content and prospects of collaborative research to respective scientists. Research reports do not constitute publication and results may be preliminary. They are included here for informational purposes only. You should contact the authors for further information. Any references to commercial products do not constitute endorsement. [ NCR-148 \| Movement & Dispersal Index \| News Index ]

Abstracts of 1998 Joint Session on

Weather Data Requirements for

Integrated Pest Management

23rd Conference On Agricultural & Forest Meteorology
13th Conference On Biometeorology & Aerobiology
Second Urban Environment Symposium

3.1
DISPERSAL OVER SHORT DISTANCES (THAT IS, LESS THAN 5.0 KM) BY SMALL INSECTS

David N. Byrne, Univ. of Arizona, Tucson, AZ

Comparatively little is known about migration and dispersal by small (less than 100 micrograms) insects moving short distances (less than 5.0 km) across agricultural landscapes. This lack of information is being corrected as more scientists address these phenomena. In our laboratory, we have been studying dispersal by sweet potato whiteflies, Bemisia tabaci, as they move from summer crops, such as cotton, into fall vegetables. Our initial conclusions were that these insects were not capable of sustained flight. Reasons included; they were members of a taxon that is almost exclusively associated with perennial hosts in the tropics, they were likely too small (ca. 45 micrograms) to have large quantities of flight fuels, and high surface to volume ratios would result in rapid desiccation in the Southwest. Early studies obtained using a flight chamber proved us wrong on several counts. In these laboratory studies, ca. 6% of the population flew for greater than 30 min. Some sustained flight for greater than 2 hr. These insects seemed to be conforming to classic definitions of insect migration, i.e., during their flight they initially ignored vegetative cues in favor of skylight cues, but eventually focused on cues mimicking plants. Mark-recapture field studies demonstrated that the majority of the population dispersed at least 2.2 km during a 3 hr-period. Further studies have shown that there is an optimal age for flight by Bemisia tabaci. Flight activity was demonstrated to be associated with changes in the flight musculature and mitochondria associated with indirect flight muscles.

Other research characterized the vertical component of their dispersal. We demonstrated that aerial density of Bemisia tabaci decreases with height above ground. Aerial whitefly density also decreased with distance from the point of take-off. We captured marked whiteflies at 7.3 m above the ground in traps at the edge of the source field, indicating a rapid rate of ascent for some individuals. Females trapped in this study were also used to determine mean egg load for insects captured at four heights (0 to 7.3 m). A highly significant negative correlation was found between height trapped and egg load, indicating that there may be a trade-off in B. tabaci between production of eggs and the ability to disperse.

Recent studies have been undertaken concerning whitefly parasitoid dispersal. The dispersal abilities of Eretmocerus eremicus have been examined in the vertical flight chamber to determine its dispersal potential. It is our plan to eventually compare their flight behavior to that of B. tabaci. Preliminary results clearly indicate that there is a statistical difference in flight duration between males (1 min av., 10 min. maximum) and females (19 min av., 93 min. maximum).

3.2
THE INFLUENCE OF WEATHER ON INTERFIELD AND REGIONAL MOVEMENT OF WESTERN CORN ROOTWORM

Scott A. Isard, Univ. of Illinois, Urbana, IL; and J. L. Spencer, E. Levine, and D. W. Onstad

Since 1993, western corn rootworm (WCR) beetle, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), the most serious insect pest of corn, have altered their movement behavior in east-central Illinois to lay eggs in soybean fields, reducing the effectiveness of crop rotation for WCR control. Now it appears that adult WCR have changed their behavior to feed on soybeans as well. On most days from late July to early September, WCR fly between corn and soybean fields to feed and lay eggs. Many of the questions relevant to the development of improved IPM for WCR require an understanding of the timing of WCR presence in soybean fields and the extent of the &amp;quot;problem area&amp;quot;.

WCR movement into a soybean field is related to solar radiation, wind speed and direction, air temperature, and precipitation with consideration of biological factors that also influence flight. WCR flight activity and meteorological variables were measured above the canopy of an 1.64 ha soybean field in east-central Illinois between late July and early September, 1997. On 14 days, insect traps were sampled at 30-min intervals. The day-to-day variation in WCR movement was large. Overall, 61% of the WCR collected were female, although this proportion rose throughout the growing season. A diel periodicity in WCR immigration to and emigration from the soybean field was observed on days conducive to beetle flight. From 601 to 1000 solar time, immigration of WCR to the soybean field exceeded emigration. Flight activity peaked between 1001 and 1200, with emigration exceeding immigration. The abundance of WCR in the field reached a minimum at this time. By 1600, more WCR were again flying into the soybean field than leaving, and WCR abundance in the soybean field reached a maximum just before sunset. WCR were not caught in the malaise traps between sunset and sunrise.

Interfield movement of WCR occur over a wide range of solar radiation loads, air temperatures, and wind speeds. Darkness, air temperatures below 15 °C or above 31 °C, and wind speeds in excess of 2.0 m/s-1 prohibit aerial movement of WCR. Within these limits, atmospheric factors had only little influence on the biologically-driven seasonal and daily temporal patterns of WCR flight activity. Atmospheric conditions were conducive to WCR flight during 62% of the 10-min measurement intervals during the growing season when biological factors enabled WCR to move among fields. Interfield WCR movement was substantially reduced by weather conditions throughout entire diurnal periods during about one-third of the days when female WCR beetles were abundant at the study site in 1997.

Region-wide sampling and modeling reveal a strong influence of convective storms on long-distance WCR dispersal. The new strain of WCR has moved from east-central Illinois eastward through Indiana to Ohio and Michigan, but is spreading only slowly to the west.

3.3
USING PHENOLOGY TO DETECT DISPERSAL OF STABLE FLIES IN WESTERN KANSAS

Carl J. Jones, Univ. of Illinois, Urbana, IL, ; and J. A. Hogsette, S. A. Isard, Y. -J Guo, Greene, and A. B. Broce

The stable fly, Stomoxys calcitrans, is a cosmopolitan pest of animals and humans found throughout most terrestrial habits on earth. Genetic studies of this insect indicate that populations in the United States may be nearly panmictic. Although larval development sites for this insect are primarily restricted to livestock operations, hence the name stable fly, large numbers of flies often appear in residential and recreational areas far from these locations. Frequent inundations of ocean beaches and lakeshore areas, known for more than 70 years in the United States, by this biting fly have had negative economic impacts on local tourism. One study, using self-marking technology, documented movement of flies to a beach in Florida from an agricultural region 225 kilometers to the northwest. However, neither the biological cause of movement nor the relationship of that cause to the atmospheric motion systems that help transport stable flies long-distances have been clearly defined.

The stable fly presents an excellent target for aerobiological studies. Large, the approximate size of a house fly, and relatively easy to find and identify because of its prominent beak-like mouthparts, the primary food sources for adult flies are a variety of large mammals. Because the stable fly is a serious pest of humans and animals, causing both economic damage and disease transmission, its physiology and behavior have attracted substantial interest from scientists for many years.

There are two techniques that can be employed to assess stable fly age. The first uses the condition of a female fly's ovaries to estimate the number of blood-meals she has taken. From that data we can estimate the number of days during which she has been in the vicinity of appropriate food sources. The second uses the amount of pterin in the eye of either sex to estimate the number of days that have passed since adult fly emergence.

To test the utility of age-grading techniques for studying the aerial movement of a stable fly population, we made collections of a large number of stable flies various distances from isolated feedlots in southwestern Kansas during 1996. Flies were collected from mid-June through the end of June, using truck mounted mobile insect traps and stationary insect traps. Stable flies were collected as high as three meters in the air. A drone aircraft was unsuccessful at collecting stable flies at higher altitudes, although a few other arthropods were collected during these aerial runs. Using the age-grading techniques described above, we were able to statistically differentiate among the mean ages of the flies collected on the feedlot, adjacent to the feedlot, and three or more kilometers from known larval development sites or bloodmeals. In addition, we were able to determine phenological differences among flies that had dispersed and those that remained near the feedlots.

3.4
CORN EARWORM MIGRATION TRAJECTORIES IN THE LOWER RIO GRANDE VALLEY OBSERVED WITH AN INSECT MONITORING RADAR

V A. Drake, Univ. of New South Wales, Canberra, A.C.T, Australia; and I. T. Harman, J. K. Westbrook, and W. W. Wolf

The Lower Rio Grande Valley (LRGV) in Texas has an abundance of host crops that can support significant populations of corn earworm (Helicoverpa zea). Adults migrate into the Valley in early March and the following generation emigrates in June. Favourable meteorological conditions can transport migrants over 400 km in one night. Field surveys and trapping are useful to establish identity and emergence trends, but provide little insight into population movements. ARS have used scanning, tracking and vertical-looking radars to study these migration flights over several seasons.

In 1996, these radar studies were supplemented with a UNSW Insect Monitoring Radar (IMR). The IMR is vertical-pointing and combines a nutating beam with rotating linear polarisation. Special algorithms allow it to automatically measure characteristics of over-flying insects that simpler vertical-looking radars cannot determine. As well as insect track, heading, and speed, the IMR can be used to estimate size, body shape and wingbeat frequency. These additional parameters improve the IMR's ability to reliably classify over-flying targets, thus providing an improved capability for monitoring population movements.

The IMR was operated from Moore Air Base near Edinburg in the LRGV in March and June of 1996. ARS deployed a network of scanning, tracking and vertical-looking radars in and north of the Valley to monitor migration from the LRGV and sources from within Mexico. Each campaign allowed the IMR to compile vertical profiles of migration intensity, speed, direction, heading, and wing-beat frequencies. All radars operated when H. zea were the predominant species emerging.

An overview of data obtained by the IMR during these exercises will be presented. Comparisons and contrasts with participating ARS entomological radars will be made. The utility of the IMR for research and operational applications in this region will also be discussed.

3.5
MIGRATORY FLIGHTS OF BOLLWORMS, HELICOVERPA ZEA (BODDIE), INDICATED BY DOPPLER WEATHER RADAR

John K. Westbrook, USDA, College Station, TX; and W. W. Wolf

Reflectivity from flying organisms including the adult bollworm, Helicoverpa zea (Boddie), is often detected in clear-air mode by WSR-88D Doppler weather radars of the NEXRAD system. During migratory seasons in south-central Texas, reflectivity from these targets reached 5 to 30 dBZ, which exceeds the lower threshold for precipitation mode. Sequential reflectivity scans showed a rapid increase in reflectivity (i.e., aerial insect abundance) over the cropped land of the Lower Rio Grande Valley by 0.5 hours after sunset. The nightly pattern of maximum reflectivity displaced approximately downwind. Results show strong positive relationships between insect concentration measured by (X- band) entomological radar and WSR-88D reflectivity, and between wind velocity and doppler velocity. Considerations due to the WSR-88D beam geometry and characteristics of insect distribution will be discussed.

4.1
CHARACTERIZING AND FORECASTING THE AERIAL FLOW OF BIOTA BETWEEN THE SUBTROPICAL AND INTERIOR REGIONS OF NORTH AMERICA

Stuart H. Gage, Michigan State Univ, East Lansing, MI; and S. A. Isard

Organisms that utilize the atmosphere for translation from one geographic place to another may flow within atmospheric motion systems along routes that are mediated by physical and biological features of the earth's surface. The pathways and timing of the flow of biota are to a large degree regular, and thus the movement of organisms in the atmosphere is predictable. This paper attempts to characterize a strategy to quantify the flow of organisms in the atmosphere in central North America. Our objective is to provide a conceptual framework to assist others interested in studying the role that the atmosphere has on the movement of organisms ranging from viruses to waterfowl.

The objective of the paper is to describe the biological and meteorological phenomenon that influences the flow of biota in the atmosphere by examining the processes from a regional perspective. In particular, we believe it is important to quantify the spatial and temporal scales at which the process of atmospheric and biological movement occurs. One of the drivers of biotic flow in the atmosphere tends to be the synchrony between biological and meteorological phenomena. The variance in this synchrony is crucial to understanding the timing and abundance of these flow patterns. The source of this variation in biological and meteorological features ranges from global scales to micro scales both in time and in space.

We plan to illustrate the array of physical and biological features that operate at multiple scales by focusing on airflow patterns and biological patterns that are characteristic of the Central US. We will characterize the confluence of meteorological components including the dynamics of Rossby Waves, the mid-latitude cyclones and the influence of landscape features such as topography and how these interplay with vegetation organization. We will examine the phenological characteristics of vegetation at a regional scale, which play a significant role in the temporal synchrony of life stages of organisms that are prone to move long distances under the appropriate meteorological conditions.

Such regional characterization of biological and meteorological systems requires a scheme for obtaining measurements of long range movement of organisms. We will examine the concept of establishing strategic sampling stations, following the example of the meteorologists who developed standards of measurement of meteorological variables long ago. We will suggest focusing on specific organisms representing the array of sizes and types that have been observed to move long distances, assisted by airflow. Finally, we will examine some of the techniques associated with the measurement of biota, the measurement of landscape characteristics and the means of analysis and communication of information about the findings.

The regional assessment of the frequency and amount of movement by organisms is gaining in importance. Development of transgenic organisms, changing patterns of weather, the mobility of exotic species and our lack of understanding of the role movement of organisms in the dynamics of ecosystems are some of the reasons for undertaking development of a plan to assess organism movement.

4.2
FLIGHT ENERGETICS AND OPTIMIZATION STRATEGIES FOR LONG-DISTANCE INSECT MIGRANTS

Robert Dudley, Univ. of Texas, Austin, TX

The energetic costs of flight influence insect migration strategies for wind-assisted dispersal as well as for intentionally directed displacement within the flight boundary layer. Small insects being convectively dispersed must nonetheless maintain a forward airspeed and offset their body weight during flight, or alternatively must reduce their flight velocity so as to hover within a moving air volume. If the goal of dispersal is to maximize the horizontal distance travelled, then flight at the minimum power speed would maximize time aloft and thus the magnitude of wind-assisted displacement. By contrast, migration within the flight boundary layer likely occurs at the maximum range speed that optimizes horizontal coverage using powered flapping flight alone. No data are presently available that assess insect airspeeds (as distinct from groundspeeds) and associated rates of energetic expenditure during predominantly convective dispersal. Moreover, aerodynamic models that predict optimal airspeeds are seriously compromised if energy stores can be replenished during migration. For boundary layer migrants in particular, the fixed availability of endogenous reserves may be substantially augmented through nectar feeding or related strategies during long-distance flights. In such cases, the optimal flight speed for maximum migratory distance may vary substantially according to the instantaneous mass and energy balance. A diversity of energetic strategies may thus characterize both boundary layer migrants as well as predominantly wind-assisted migratory forms.

4.3
A FRAMEWORK FOR STANDARDIZING FLIGHT CHARACTERISTICS FOR SEPARATING BIOLOGY FROM METEOROLOGY IN LONG-RANGE INSECT TRANSPORT

Gary L. Achtemeier, USDA Forest Service, Juliette, GA

One of the most exciting questions raised by studies of long-range insect transport is "Once airborne, to what extent do insects contribute to their destination?" Radar studies showing layers of insects flying at or near the level of the low level jet and with peculiar orientation lend credence to the view that these biota are in some way participating in their migration. A simple modeling approach is hypothesized to separate biology from meteorology in long-range insect transport. Measurements of the thermal structure of the atmosphere through which insects are flying can be combined with terminal velocity and ascent rates for an ensemble of insects to model expected insect behavior. Departures from model predictions should be caused by higher-order meteorological phenomena and biology. Continued refinements of the model should isolate the biology of long-range transport, if any.

4.4
GRASSHOPPER MIGRATORY TENDENCY AS THRESHOLD TRAIT

Jack W. Kent, Univ. of Texas, Austin, TX; and M. A. Rankin

The North American migratory grasshopper Melanoplus sanguinipes (Fabricius) has engaged in spectacular outbreak swarms several times in the 20th century, and substantial numbers of individuals in many populations perform long-distance flights even in non-outbreak years. In the field, migratory flights typically begin under specific conditions of light, temperature, and windspeed that can be simulated in laboratory tethered-flight experiments. There is individual variation in migratory tendency, both within and between populations, that appears to have a substantial genetic basis; movements of grasshopper populations are therefore influenced by both environmental and internal cues. Previous work has found that (1) tethered-flight performance in the laboratory is correlated with migratory tendency in natural populations; and (2) tethered-flight performance is bimodally distributed, because individuals tend either to not fly (or fly for only a few minutes), or to fly for much longer than one hour. In the present work, we analyze migratory tendency as a threshold trait, using performance of 60 - 80 min of tethered-flight in at least one of three trials as diagnostic of a prospective migrant. In a laboratory population derived from a migratory Arizona population, heritability of migratory tendency is estimated to be in the range 0.3 - 0.5. In males, artificial selection on the frequency of flights 60 - 80 min in duration increases both the frequency and the mean duration of flights > 60 min. Previous work suggests that while carbohydrate is the principal fuel for short flights and flight initiation, lipid is the principal fuel for long-duration flight. Therefore, in this study we examine the correlated response of characters relating to lipid metabolism to artificial selection on migratory tendency. These characters include lipid reserves as percent of body mass, thoracic volume, relative size of thoracic lipid reserves, and amount of adipokinetic hormone (AKH) stored in the corpora cardiaca.

4.5
DEVELOPMENT OF A DATA ACQUISITION SYSTEM FOR LONG-TERM OUTDOOR RECORDING OF INSECT FLIGHT ACTIVITY USING A PHOTOSENSOR

Aubrey Moore, Northern Marianas College, Saipan, Commonwealth of the Northern Mariana Islands

Hardware consists of an upward-looking photosensor connected to a personal computer via the microphone jack of a 16-bit sound card. A custom-written Windows95 program monitors the voltage output from the sensor which is continually digitized by the sound card at a rate of 8000 samples per second or higher. Reflections and shadows of individual insects flying between the sun and the photosensor trigger the recording of transient signals which contain species-specific wingbeat waveforms that are typically rich in harmonics. Cepstrum analysis filters out low harmonic-content signals triggered by environmental noise. Waveforms passing through the filter are stored on disk with a time stamp so that they can be correlated with solar radiation, air temperature, speed, and direction monitored by an automated weather station. The system is designed to run unattended for weeks at a time. Analysis of flight activity data from long-term field tests of the system on the island of Saipan will be presented.

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