February 2, 1998

9 Min Read
Swarm fronts

When asked what his studies had revealed about the nature of Creation, pioneering genetic biologist J.B.S. Haldane replied: "The Creator has an inordinate fondness for beetles."

Insects compose most of the animal biomass on the planet. In many ways, entomologists are at the vanguard of what Ian McRae, professor of entomology at the University of Minnesota, calls "applied ecology." On a West African savanna or in a New Jersey laboratory, these biologists turn to engineers to equip them with the instrumentation, systems, and other tools of discovery required to track populations and study the behavior and physiology of individuals.

Eye in the sky. They were the teeth of the wind, the eighth plague of Egypt. Today, locusts remain the scourge of croplands throughout Africa and the Middle East. A given swarm might cover 20 X 5 kilometers with a population density greater than 300 adults per square meter. During the 1986-1989 plague in East Africa, locust containment efforts cost approximately $275 million and still the swarms managed to gobble up to 5% of the region's crops.

The Migratory Pests Group of the United Nations' Food and Agriculture Organization (FAO), headquartered in Rome, Italy, is the early warning system for many of the 46 locust-affected countries. To this end, the self-described "small but extremely active" group within the FAO's Plant Protection Service has developed the Reconnaissance And Monitoring System of the Environment of Schistocerca gregaria (RAMSES) information system. Schistocerca gregaria is the scientific name for the desert locust. RAMSES combines GPS-referenced databases and desktop mapping capabilities to provide information on the location and condition of food crops and whether they are exposed to the potential threat of locusts.

Michael Cherlet, project manager for the FAO's remote sensing technology program, says satellite imaging data is a valuable tool in forecasting and monitoring locust swarms. "Remote sensing is essential for detecting potential breeding grounds in order to direct the spray teams more efficiently to possible targets," Cherlet explains. "Because locust outbreaks are dependent on rainfall, weather satellite data are useful predictors."

Here is how RAMSES works: Researchers identify the cold tops of rain-producing cumulo-nim-bus clouds from satellite images by their thermal signatures and process them into ten-day Cold Cloud Duration (CCD) composites. This indicates a probability for rainfall, which increases with prolonged cloud duration. The CCD composites are used to build a profile of possible locust activity for a given area using commercially available geographic information systems (GIS).

Vegetation data are obtained using the U.S. National Oceanographic and Atmospheric Agency's (NOAA) Normalized Difference Vegetation Index (NDVI). NOAA satellite imaging data with one-kilometer resolution are processed at the local receiving station to produce a ten-day maximized composite image. This image, combined with the ten-day CCD image, results in a picture of the region's locust potential based on meteorological and vegetation factors.

"The NDVI picks up vegetation fairly well, but the problems with reliability start in the desert, our area of interest," Cherlet admits. "The sandy soils, high in quartzite contents, reflect infrared very much like high vegetation areas. This means that in some places the NDVI is significantly over-estimated." Cherlet's group currently is devising a methodology to correct for soil interference in the NDVI calculation.

In the U.S., fortunately, locusts are not the problem. In what is perhaps another irony, habitat destruction on the Great Plains has banished the teeth of the wind from North America in modern times. "In my opinion, we will never see great locust swarms here again," says the University of Minnesota's McRae. "But some garden-variety grasshoppers cause damage enough."

McRae is applying remote imaging, GPS, and GIS technology in an effort to locate even more insidious forms of infestation. While locusts and grasshoppers at least have the courtesy to dine on leaves, in plain sight, other insects prefer to go for the roots or other concealed parts of plants. McRae runs the Northwest (Minnesota) Experiment Station, a "scientific farm" producing row crops, such as corn and sugar beets, that even has dairy facilities. Various grubs, caterpillars, and maggots are invited for dinner.

Each insect species has trademark feeding techniques, which in turn produce telltale plant damage. Satellite images reveal variations in color reflectivity levels, indicating plant damage of a particular type and extent. One problem: "By the time damage shows up, it is almost too late to do anything about it," McRae says.

Therefore, images of color reflectivity levels are only the starting point. McRae correlates them with field observations of teams equipped with GPS receivers for pinpointing areas of infestation. The data are entered into GIS systems to produce extremely accurate maps. Field teams use the MapInfo software from Mapping Information Systems Corp., Troy, NY, on laptops. More sophisticated GIS investigations are carried out in the lab using Arc/Info from Environmental Systems Research Institute Inc., Redlands, CA.

Rearing their ugly heads. While some entomologists view the world as their laboratory, others strive to bring the world into the lab. Pesticide-maker American Cyanamid Co., Princeton, NJ, has constructed a world-class insectory where 100 million individuals of 13 different species are reared annually. Many of these insects become fodder for the company's pesticide development efforts, while others remain to ensure a future supply of healthy subjects.

According to William Fisher, senior research biologist for the Agricultural Products Research Division's identification and advanced testing program, running an insectory requires equal parts biology and engineering. It might seem that getting bugs to breed indoors should not be such a chore. Unfortunately (or fortunately, depending on your point of view), this is not the case.

"The chief enemy of insect populations in the laboratory is disease," Fisher says. One particular virus, NPV, is the bane of insectories, spreading readily and killing quickly. "The layout of our facilities, the design of the cages and work areas, and especially the procedures for handling insects all must take disease prevention into account."

In terms of feeding, many of the moth species eat a diet containing seaweed, soya flour, wheat germ, and vitamins (not bad!). Sucrose is added to stimulate feeding. 200 liters of diet are prepared each week and transferred by hand to trays containing 32 wells. Each well becomes the temporary home for one or more larvae. The trays are sealed with a Mylar film, perforated to permit moisture to escape. This is important as the diet has a water content of 80%.

Hand-filling the feeding wells is time-consuming and repetitive work, and therefore a prime candidate for automation. Fisher is developing a feeding system that uses a filler unit from National Instrument Co., Baltimore, MD, common to packaging industries for handling viscous substances, such as mascara and petroleum jelly. A custom-designed dispensing head is used to squirt precise and uniform amounts of diet into tray wells in seconds without producing temperature stratification.

Cages are designed specifically for each species. Wherever possible, the design uses the behavior of the insect to best advantage.

Care is taken to prevent an invertebrate version of "The Great Escape." Bands of Fluon coating (a polytetrafluoroethylene) from ICI America Inc., Wilmington, DE, below the inside rim of the cockroach tanks keep the Roach Motels in the corners vacant. Water moats contain the aphids in their black bean castles. Bug zappers deal with slender diamond-back moths that slip out.

One of the most intractable problems in the insectory is the unbelievable abundance of moth wing scales. If you have ever handled a moth, you will be familiar with the powdery substance inevitably left on your fingers. Multiply this times the hundreds of thousands of moths active at any given moment and you have a veritable cloud of scales. These can pose allergy or respiratory problems for workers and act as agents for spreading disease in the event of an outbreak.

Storing moth cages (suspiciously reminiscent of gallon ice cream containers) in Airegard Airflow Workstations from NuAire Inc., Plymouth, MN, effectively eliminates the airborne scale threat. These filtration systems produce a laminar flow with uniform horizontal velocity catching 99.99% of particulate matter of 0.3 microns in their High-Efficiency Particulate Air filters. The systems are used in a variety of industries to create a particle-free, bacteria-free clean-air environment needed for laboratory work, testing, manufacturing, inspection, or pharmaceutical procedures.

Environmental control does not end with insect storage units. Each of the eleven rooms in the insect-rearing area has independent temperature and humidity controls tuned to suit the tastes of the species living there.

"Running an insectory is a study in managing variables," Fisher concludes. "You use the right equipment and procedures to eliminate 99% of the variables you can do something about. This leaves you free to pay attention to that 1% of the variables not under your control."

People seem to be most aware of their six-legged neighbors when they are preparing to slap, squish, or spray them. Nevertheless, the six-part documentary, "Alien Empire," a presentation of the long-running series, "Nature," concludes with this summation about the respective places of mankind and insects in the order of things: If insects disappeared tomorrow mankind would not survive, but if mankind disappeared insects would hardly notice.

If we can't live without insects, at least engineers are providing the tools to help us live with them better.

Engineering Challenges

Model and observe complex systems by:

- Developing infrared and near-infrared sensors that distinguish reflected light better than existing systems

- Designing improved filtration systems to achieve laminar air flow over work areas, and better filters for catching particulate matter

- Automating to achieve process consistency

Other applications for biology technology

- Satellite imaging in meteorology, oceanography, and land management

- GIS in civil engineering and environmental modeling

- Filler systems for process industries handling viscous substances

- Filtration systems for particle- and bacteria-free manufacturing processes

- Coatings to reduce friction in mechanical systems

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