Producer and consumer safety are important considerations when making decisions about insect management. Choosing low-toxic control options will help keep you safe and increase consumer confidence in your product. Diatomaceous earth (Insecto, Protect-It, etc.) is one such product that can be used as a topdressing. This substance is milled from the silica-rich cell walls of fossilized sea algae. As insects crawl through the grain, their hard cuticle coverings are abraded by the sharp edges of the diatomaceous earth. The insects then desiccate and die. Diatomaceous earth should be used to treat the first loads in the bottom of the bin and the last loads in the top. As with any treatment, use proper protection and caution; diatomaceous earth can be irritating to workers, particularly those that breathe the dust, so use personal protection equipment as necessary. Keep in mind that diatomaceous earth can abrade equipment.
Insect-growth regulators are also a relatively safe option. These compounds, such as methoprene, mimic naturally occurring insect hormones and prevent the development of larvae into adults. These compounds do not prevent damage by insect larvae, but instead promise to stop insect populations from cycling by preventing development of adults, which are the reproductive stage of insects. Because adults do not develop, new eggs cannot be laid and future generations are prevented.
As mentioned above, Bt when applied as an insecticide can provide highly selective control for moth larvae; however, if grain being stored is “Bt corn,” the grain may have some protection against larval moth damage. There is evidence that Bt corn provides a degree of protection against stored-product pest caterpillars like the Angoumois grain moth and Indian meal moth. On the other hand, there is little evidence to suggest that strains of Bt active against corn rootworm larvae, which are immature beetles, provide any control of weevils or other beetles that are stored-product pests. Keep in mind that little research has been done testing the effectiveness of Bt grain in stored conditions, so continue to sample grain for pest presence.
Carbon dioxide can also be used as a safer fumigation alternative, but the bin must be completely sealed. While the bin is sealed and fumigated over several days, the carbon dioxide keeps the insects’ respiratory openings open; the pests then dehydrate. Heating or cooling the bin to extreme temperatures may also kill some species. Biological control using beneficial natural enemies is another option; some companies sell species that attack maize weevil, granary weevil, confused flour beetle, lesser grain borer, sawtooth grain beetle, and Indian meal moth.
Eliminating unnecessary chemical applications improves food quality and saves money. Be sure to properly identify insect pests; many are very small and have only subtle characteristics. Some fungus-eating beetles can appear to be pests of the grain itself. However, their presence indicates a different problem: high moisture levels. To be certain of the identity of a stored-grain pest, consult a professional.
Some insects are becoming resistant to various chemicals, most notably malathionand phosphine. A few populations of insects (Indian meal moths, red flour beetles, lesser grain borers) are resistant to malathion control, so treatment is ineffective. Although they are labeled as grain protectants, malathion dusts are not recommended. Insect resistance is widespread and the public is concerned about malathion residues in food, so its use is discouraged. Phosphine resistance is a newer challenge that has spread across the Midwest and perhaps farther; the status of resistance to phosphine gas in Pennsylvania is unclear.