[Pest Control] Stored Product Pests

Aerosol insecticides are liquid formulations that are atomized and applied through a nozzle. They kill exposed flying or crawling insects and, in contrast to fumigants, do not penetrate food material, packaging, or equipment. They often are formulated with a carrier, such as a petroleum-based product, to facilitate dispersal throughout the facility where the aerosol is applied. Ultra-low-volume (ULV) insecticides are a type of aerosol that can be applied without a carrier, or with reduced rates of the carrier compared to some aerosol formulations. The food industry has questions regarding the effectiveness and dispersal of aerosols, including ULV insecticides, in commercial sites where grains are processed or milled or where finished products are stored as packaged goods. As part of our research program with the USDA-Agricultural Research Service in Manhattan, Kan., field trials were conducted in which adult and immature stages of the red flour beetle and the confused flour beetle were exposed to different ULV insecticides inside commercial facilities.

The first set of trials was conducted in a 600,000 cubic-foot room inside a large commercial facility in which a delivery system from Entech Systems in Kenner, La., was installed. The insecticide used in the trials was a mixture of 1 percent pyrethrin and synergists, applied at the label rate of 1 ounce per 1,000 cubic feet, along with a carrier at rates specified on the label. Inside the room, ten red flour beetles and ten adult confused flour beetles were exposed in separate plastic dishes, with and without a small amount of flour, at 15 locations on the floor of the room. At each location, ten mature larvae and ten pupae of each species also were exposed in separate sets of four dishes with flour. The dishes containing the insects were exposed to the ULV insecticide for two hours, removed and transported back to the lab at the USDA Grain Marketing and Production Research Center in Manhattan, Kan. Adults were held for two weeks, while the larvae and pupae were held for three to four weeks to ensure completion of adult emergence.

After one week post-exposure, survival of adult red flour beetles was 2.2 percent with flour and 3.5 percent without flour, in contrast to survival of the confused flour beetle, which was 13.1 percent with flour and 4.5 percent without flour. After two weeks, survival of red flour beetle was 0.1 percent with flour and 1.3 percent without flour, while survival of confused flour beetle was 9.5 percent with flour and 3.7 percent without flour. The confused flour beetle was the more tolerant species, and the presence of the flour food source led to an increase in survival after application of the ULV insecticide. The immature stages were more susceptible than the adults. All larvae of both species exposed to the aerosol died as larvae or discolored pupae. No exposed red flour beetle pupae emerged as adults, while emergence of confused flour beetle pupae was sporadic and less than 1 percent.

A series of tests also was conducted in which mature larvae of the confused flour beetle and the red flour beetle were exposed to the insect growth regulator methoprene (Diacon II) at the label rate of 3 ounces per 10,000 cubic feet, using the test room and application procedures described above. However, in this test the larvae were exposed in dishes with flour in open areas or underneath pallets, which were called obstructed areas. No adults developed from the larvae exposed in open or in obstructed sites, indicating good dispersal of the insecticide.

In the final test, a series of exposures was done in a commercial milling facility by exposing pupae of the red flour beetle with flour in plastic dishes placed in open or obstructed areas, or in hidden areas which would be a barrier to ULV dispersion. The insecticide was a mixture of the label rates of both pyrethrin and Diacon II, using the same Entech application system. There was little or no adult emergence from pupae exposed in open or obstructed areas, but about 50 percent of pupae exposed in the hidden areas emerged as adults.

The results of these field studies show that ULV insecticides and aerosols could be used to control insect pests inside milling, processing and storage facilities. If a food source is present, it could lead to survival of adults exposed to the insecticides, which shows that cleaning of residual material and overall sanitation could have a beneficial impact on pest management.  However, ULVs and aerosols are not one-time applications, in contrast to fumigations, and it may be necessary to apply the treatments on a frequent basis. In addition, an insect monitoring program would also be beneficial to help assess the impact of ULV or aerosol treatments.

The author is a research entomologist with the USDA in Manhattan, Kan. For more details about this research or additional information, please contact him at 785/776-2783, or frank.arthur@ars.usda.gov. This summary was adapted from a presentation to the Food Protection Committee of the International Association of Operative Millers, and is strictly a report of research. Mention of a specific company or an insecticide does not constitute a recommendation or endorsement by the U. S. Department of Agriculture.