The largest amounts of methyl bromide used in Canada are primarily for fumigating mills and food processing plants. Therefore, it is not surprising that Canada has taken an active role in seeking methyl bromide alternatives. One possible option is the use of heat treatments.

Heat treatments to control stored-product insects is not a new practice for the Quaker Oats food processing plant in Peterborough, Ontario. A successful structural fumigation combining heat, phosphine, and CO₂ was conducted in 1996. Once again, the Quaker Oats facility donated its mill facility for a combined heat treatment field test. This time the combination used was heat and an enhanced diatomaceous earth (EDE) formulation, which is made from the fossilized skeletons of diatoms—single cell algae—and causes dehydration and damage to insect cuticles.

Processing facilities have been using heat combination treatments instead of, or in combination, with methyl bromide for more than 15 years. But many processors have concerns about the cost of heating equipment, the need for more frequent treatments, and the possible damage to buildings and equipment.

"USDA and Agriculture and Agri-Food Canada (AAFC) teamed up to find alternatives to methyl bromide. We began investigating ways to address some of the concerns about heat treatments," says Alan Dowdy a research entomologist with USDA's Agricultural Research Service, U.S. Grain Marketing Research Lab in Manhattan, Kansas.

"The Quaker Oats facility was an ideal place to test this trial, because it is typical of many other milling and cereal-processing facilities. It has a low relative humidity, like many food processing facilities. Some sections are more than 75 years old. Its structure consists of old, timber beams and floors, stone walls, and cement-on-soil surfaces—which make heat treatments difficult. These conditions help increase the efficacy of our tests," says Paul Fields, a research scientist with AAFC.

Four different treatments using heat alone, EDE alone, heat and EDE, and no heat or EDE were examined. Three different buildings and areas were used for the tests: (1) the oat mill—located in the basement of one building, (2) the hallway of another building, and (3) the equipment storage and cardboard compacting area—located in the basement of another building. The entire facility was cleaned the evening before the heat treatment.

In preparation for the heat treatment, different areas of the mill were treated with EDE as a powder using a power sprayer, a dry powder using a hand duster, a 20-percent liquid solution using a hand sprayer, or distributed in measured amounts of 1, 3, and 7 g/m² in plastic rings (15 cm diameter, 2 cm high, 0.018 m² area) placed on the floor. EDE, one of the main grain protectants, is a type of insecticide that works by sticking to and absorbing the waxy coatings on insects, causing their death by dehydration, says Dowdy.

The plastic rings allow the insects to be exposed to the heat treatment with space to move but prevents their escape into the food processing facility. The rings are sealed along the outside with plasticine to prevent bugs from escaping through cracks between the rings and the floor. Three rings, placed about 5 cm apart, are used for each treatment.

"We used adult confused flour beetles (Tribolium confusum) in our commercial test, because they are the main insect pest of food processing facilities. We placed them in vials with 10 grams of flour 2 days prior to the test, which was conducted March 14-16, 1997. Fifty beetles were placed in each ring between 3:00 and 5:00 p.m., on March 14. We checked mortality every 60 minutes and removed any dead insects," says Fields.

"In the heated areas, we found that the dry application of EDE gave a 100-percent death rate of the adult beetles after 13 to 22 hours and 106 ^oF compared to untreated insects, which required 32 to 38 hours and 115 ^oF to 117 ^oF," says Dowdy.

Relative humidity started at 19 percent and declined to 5 percent during the entire test. Peak temperatures were at or above 122 ^oF during the treatment.

This project demonstrates the effective combination of heat plus diatomaceous earth and the potential to reduce the temperature or time requirements necessary for effective insect control. (For a complete report on this project, contact Alan Dowdy, phone 913-776-2719; fax 913-537- 5584. Or visit the website at href=http://res.agr.ca/winn/Heat-DE.htm)