This article originally appeared in the October 1990 issue of the Water Survey's Currents newsletter. For more about this work, check out the article titled "A helicopter-mounted isokinetic aerial insect sampler" published in the Journal of Economic Entomology in 1991.
A helicopter equipped with special insect traps has been roaming the skies over central Illinois since midsummer. The object is to capture corn leaf aphids, tiny bugs about the size of a large typed period.
Researchers from the Illinois State Water Survey, the Illinois Natural History Survey, and the University of Illinois are trying to learn how weather governs the migratory behavior of the corn leaf aphid. This aphid is a scourge of corn, sorghum, small grains, and other crops—not because it's a big eater, but because it carries some very destructive plant viruses. The viruses it transports cause significant crop damage and monetary losses to the agricultural sector in Illiois and other Midwestern states.
The researchers' observations will help scientists predict insect pest arrival in Illinois, so that growers and Cooperative Extension specialists can be alerted in time to take precautionary action. Thus in the near future, farmers will be better prepared to reduce pest damage through more timely application of less potent pesticides.
The three-year project, which began in 1989, is funded by the U.S. Department of Agriculture. Steve Hollinger (Water Survey), Michael Irwin (Natural History Survey), and Scott Isard (University of Illinois) are the principal investigators.
Tracking the Pest
Each spring and summer, corn leaf aphids invade Illinois and other Midwestern states, "riding the wind" over long distances from their winter homes in the Gulf Coast states. The researchers suspect that the aphids' flight patterns are controlled by certain atmospheric conditions.
"We're trying to determine what factors govern the elevations at which aphids fly," says Hollinger. "We know they tend to fly in specific atmospheric layers. We want to know the meteorological conditions within the layers that carry large concentrations of insects.
"We also want to find out the weather conditions in which aphids will land and take off, and what triggers their migratory behavior. When we know all this, it will be possible to forecast major influxes of aphids to Illinois and other states."
The Bird and Its Prey
To collect the insects, a helicopter piloted by Rick Jachowske, maintenance foreman at the Univeristy of Illinois Institute of Aviation, makes a series of five-minute horizontal passes over farm fields near Champaign. During each pass, the helicopter is flown at a predetermined altitude ranging from 300 to 6,000 feet.
"We fly at different elevations to find out where the insects are and what physical factors of the environment are concentrating them in these zones or layers," says Hollinger.
Two specially designed collectors mounted on the helicopter skids trap insects. The bugs suffer little damage because expansion chambers in the collectors reduce the impact velocity.
During each helicopter flight, balloon-launched radiosondes (miniature radio transmitters) are released from the ground into the lower atmosphere in the area of the flight. These instruments use radio signals to relay data on pressure, temperature, and humidity to computers on the ground. Wind speed and wind direction are determined by tracking the balloon. Temperature, pressure, and wind speed are also measured by sensors mounted on the helicopter.
The data from the radiosondes and the helicopter are combined to construct profiles of meteorological conditions; these profiles are then studied to determine which factors govern the aphids in migratory flight.
Pest Brought to Rest
After the helicopter lands, the trapped insects are taken to an entomological laboratory at the Natural History Survey. The corn leaf aphids are then quick-frozen in a -80 F freezer for subsequent soluble fat (lipids) analysis. The analysis process includes placing the aphids in an oven at low temperatures for 24 hours and dipping them in an ether solution to extract lipids.
"The lipids analysis is used to separate insects of local origin from those that have flown long distances," says Irwin. "An insect has finite energies for flight. Consequently, the longer it has flown, the more of its total lipids, or total flight fuels, will have been expended."
The researchers are currently building a chamber to simulate conditions experienced by aphids during flight. As aphids fly in the chamber, wind, temperature, and other factors will be controlled.
"These experiments will help us determine the stimuli that aphids respond to during flight," Isard says. "They'll also help us learn if aphids search and track certain types of atmospheric zones, or if they're passively transported to different zones through physical mechanisms."
