Illinois Natural History Survey - University of Illinois

Helicopter Captures Russian Wheat Aphids

Russian wheat aphids (RWA), Diuraphis noxia (Mordvilko), were introduced into the United States less than 10 years ago. Since that time they have spread rapidly throughout the drier regions of the western United States and Canada, where they are major pests of many small grains, particularly wheat and barley. RWA suck the juices from these plants, stunting their growth and substantially reducing grain yields. These aphids reproduce quickly in leaf sheaths of small grain plants, where they are protected from predators, parasitoids, and pesticides.

Knowledge of the dispersal dynamics of RWA is critical to improving our ability to monitor and predict infestations of these aphids. RWA dispersal may be either local or long distance, depending in part upon atmospheric conditions. Before we can forecast aerial movements of this important pest, we need to understand the meteorological factors that govern the vertical distribution of RWA in the atmosphere. Because wind speed and direction often change dramatically with altitude above the earth's surface, the flight paths and destinations of weak-flying insects such as RWA can differ substantially, depending upon their altitude of flight.

Local movements of RWA generally occur on clear, warm days when the sun heats the earth's surface, producing convection (rising air parcels) in the lower atmosphere. These thermals can carry weak-flying insects upward, often as high as 1 mile. Subsiding air parcels return many insects to the ground, usually in the local environment or a few miles downwind. At night the atmosphere generally becomes stable and layered. On clear evenings, warm air layers with strong southerly winds (low-level jets) often develop after dark from 500 to 1,000 ft. above the ground. Weak-flying insects caught up in the lower atmosphere in late afternoon often find themselves in these low-level jets, where they can remain until morning. Winds in these jets can exceed 20 m.p.h.; consequently, insects that ride them all night can find themselves hundreds of miles downwind by morning.

Helicopter used in RWA dispersal dynamics study. (photo by Gail Kampmeier)

The objective of our multi-disciplinary, multi-institutional research team was to investigate the dispersal dynamics of the RWA on the high plains of eastern Colorado. The research project was funded by the Western Regional Integrated Pest Management (IPM) Grant Program and the National Science Foundation. The University of Illinois contingent of the team consisted of Gail Kampmeier and Michael Irwin (Illinois Natural History Survey [INHS] entomologists), Scott Isard (biometeorologist, UI Department of Geography), Mark Belding (electronics technician, Illinois State Water Survey [ISWS]), and Rick Jachowske (helicopter pilot, UI Institute of Aviation). This group was charged with collecting RWA and concurrently taking meteorological measurements (pressure, temperature, humidity, and wind speed and direction) throughout the lower atmosphere. To achieve this, Doyle Dazey (INHS) hauled the UI's helicopter and insect collection pods to Greeley, Colorado, where entomological and CHILL radar teams from Colorado State University joined us for two intensive field programs, each lasting two weeks, during May-June 1993 and 1994. The CHILL radar was developed by researchers at the University of Chicago and ISWS.

Much of the instrumentation used in this research was developed and tested in the mid-1980s as part of the Pests and Weather Project funded by the Illinois Department of Energy and Natural Resources. During that three-year project, scientists from INHS, ISWS, and the University of Illinois studied how weather influences the immigration to Illinois of important agricultural pests, particularly the corn leaf aphid.

Our large torpedo-shaped insect collection pods are unique. The helicopter carries one collector on each of its two skids. During flight, the volume of air flowing through each pod is continually regulated by a computer-controlled set of fins at the rear of the collectors. After passing through the forward orifice of the pods, the air enters an expansion chamber where its velocity is reduced. The insects contained within it are slowed down and funneled, relatively unscathed, by a cone-shaped screen mesh into small collection chambers. Each pod can collect 12 samples during a single helicopter flight.

This technology allows us to sample a predetermined volume of air at multiple altitudes in a single helicopter flight. When the pilot reaches the first altitude to be sampled, he pushes a button on the computer causing the first door of the collection chamber to close. The computer monitors the air flowing into each pod until the prespecified volume has been sampled (usually 1,000 m3 in about 5 minutes), at which time a second door automatically drops, sealing the sample. The pilot then proceeds to the next flight altitude where he repeats the procedure. We generally flew two or three flights per day over the two-week periods, each flight lasting nearly two hours. When the helicopter returns to the airport, insects are removed from the collection chambers, counted, and identified to order. Live RWA are frozen so that they can be analyzed for flight fuels to determine how long they had been flying.

Free-floating radiosonde probes (automated weather data collection devices) attached to helium-filled balloons were used to determine atmospheric conditions at the same times and in close proximity to the actual atmospheric volume from which the aerial insect collections were made. The sonde transmits pressure, air temperature, and humidity readings every 10 seconds as it rises through the atmosphere to our Atmospheric Data Acquisition System. Visual tracking of the bright red balloon using a theodolite allows us to determine wind speed and direction. These important meteorological factors are displayed graphically in near-real time at the base station.

Russian wheat aphids inhabiting a sheath of winter wheat. (photo by Gail Kampmeier)

The CHILL radar was operated throughout each collection flight in Greeley, sweeping the atmosphere for return echoes from insects (traditionally referred to as angel echoes). In addition to insect layer concentrations (which could be "seen" up to 50 miles away), the CHILL could detect the position of the helicopter. Information on both the meteorological conditions and the location of insect concentrations in the lower atmosphere was radioed to the pilot and used to direct the helicopter to specific atmospheric layers for sampling.

We caught over 400 arthropods in 1993; unfortunately, none of them were RWA. However, nearly six times as many arthropods were trapped in 1994, with one-quarter identified as aphids (600) and over half of those were RWA (339). RWA were abundant relatively high in the atmosphere especially on sunny days characterized by warm southerly winds. In the early morning of 6 June, 1994, RWA and other insects were collected throughout the lower atmosphere, including a number within a low-level jet blowing from the south at 22 m.p.h., about 2,200 ft. above the ground surface. Below the jet the atmosphere was stable, so it is likely that the insects we caught within these air layers were of local origin. However, if the insects that we found higher in the atmosphere had traveled in the low-level jet throughout the night, then they likely were immigrants from 150-250 miles further south, where large overwintering populations had been found in 1994. Samples from later the same day revealed that RWA were very abundant throughout the lower atmosphere. The highest altitude at which we caught RWA was approximately 5,000 ft. above ground level. RWA were not trapped in airstreams with temperatures below 54 degrees F.


Mark Belding of the Water Survey calibrating on-board computer in helicopter used for RWA study.

(photo by Gail Kampmeier)

Other well-represented aphid species in the collections included small grain pests, such as the bird cherry-oat aphid, greenbug, and English grain aphid. The pea aphid, a prominent pest of alfalfa, was also present. Flies, wasps (mostly parasitic), leafhoppers and planthoppers, true bugs, spiders, a damselfly, a few small moths, thrips, mites, and many very small rocks were also trapped.

Acknowledgments: The Colorado research team was led by Tom Holtzer, with Mark Carter, Ian MacRae, Tim Burton, and Chuck Lang (entomologists, Colorado State University), and student Derrick Nabel. Patrick Kennedy, Eugene Mueller, and Kenneth Pattison operated the CHILL radar. Monfort Inc., graciously donated the use of its aircraft support facilities for the field programs in both 1993 and 1994. We especially thank John Warrender, Ken Ferguson, and Matt Yakel for their tolerance and support of our activities.

Gail E. Kampmeier, Scott A. Isard, and Michael E. Irwin, Center for Economic Entomology

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Last Modified 3/19/96

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