• Chelle Hartzer

A "National Day" for Everything (AKA: I'm making cookies)

Apparently, March is National Flour Month. It’s also National Invasive Species Week this week. It only makes sense to feature flour beetles for this blog post in order to celebrate.



These are thought to originate in Indo-Australian and African regions and were likely brought over by some of the first settlers to the US, so technically, and invasive species.

While they are often lumped together, there are actually many flour beetles. According to the ESA common names database, there are nine. Two of the most common are the red flour beetle and the confused flour beetle (Tribolium castaneum and T. confusum).


As the name suggests, they do feed on flour. While they can not develop on whole, intact grains, they feed on many other types of grain products, dried fruits, nuts, milled grains, and more. Diet will affect how quickly they can develop and their adult lifespan. In general, they can develop from egg to adult in about 30 days. Adults are long-lived and can live up to a year or more. All that time, they are dropping eggs and continuing the population growth.


There has been considerable research done on the Tribolium species, particularly when compared to other stored product pests. The red flour beetle has had it’s genome sequenced and quite a bit of genetic research has been conducted. There has been extensive work done on their cold and heat tolerances and how that impacts their development. Treatments such as insect growth regulators (IGR’s) have been researched as well showing that they are very effective.


Of course, the main question for many: how do we control it. Flour beetles can cause massive feeding damage, grain quality issues, and contamination. No one wants to open a bag of flour and find beetles crawling around inside (yet flour is still packaged in flimsy paper bags…). An integrated approach of sanitation, exclusion, monitoring, and treating is the best option.

Sanitation is often touted as the “best” option. It sounds great: clean up all the food sources and all the problems disappear. Great! How can you possibly clean up all the food in a food processing site like a flour mill? Or all the ingredients from a bakery? Or all the dry products from a grocery store? While it sounds easy, (just clean everything) in practicality it is really difficult (HOW do you clean EVERYTHING?). The trick is trying to limit the amount and the access to food sources. This means removing as much spilled food as possible on the production floor. Incoming raw ingredients should be inspected and stored in sealed packages (if possible) until they are ready to be used. First in-first out procedures should be used so products get used in the order they have come in. This way, ingredients or finished goods don’t sit for long periods of time, making them more susceptible to infestation.

Monitoring is essential and this can’t be stressed enough: if you don’t know where beetles are or in what numbers, you can’t possibly target them for treatment. There are very good pheromone monitors for flour beetles and most of the common stored product pests. These should be checked every week to two weeks. It points to areas where flour beetles are so inspections and increased sanitation can occur. The areas where monitors show no or little flour beetle activity can be a lower priority. Increasing numbers being captured might indicate a lack of sanitation, incoming infested products, or failures in treatments. The opposite, finding decreased populations can mean that the extra sanitation worked and treatments were effective. Without monitors, it’s a guessing game and time is wasted inspecting and treating areas that may not need treatment.


Here’s a run down of the research from the past year and how it impacts the management of flour beetles:

  • Insecticide netting is effective in killing flour beetle adults. This could translate into wall coverings and packaging liners to keep populations down. A very interesting aspect of this research was that beetles were more likely to die when exposed mid-day or later, as opposed to earlier in the day. Should we schedule treatments for late afternoon for greater efficacy?

  • Even a few flour beetles are enough to change the composition of finished flour after a month in storage. They found moisture was increased, uric acid was present, and microbial counts were increased. Using a fine enough sifter to filter out contaminants (like insects) and storing finished goods properly to prevent infestation is important.

  • Flour beetles are found worldwide but can have slightly different development times depending on where they are found. Some strains will lay more eggs, have faster development times from egg to adult, and have longer adult lifespans. Making sure sanitation is done weekly can disrupt this life cycle and treatments on a monthly basis can help too.

  • Adult flour beetles can tell the temperature. Okay, that’s stretching it, but they found that at more “normal” temps, flour beetles would most often be hiding inside piles of flour/grain instead of out in the open. This means it is essential to clean up large amounts of spilled product so beetles are forced out and treatments can contact them more.

  • They need their protein. They can survive on brewer’s yeast alone and actually do better with higher protein sources than higher carbohydrate sources. This means if there are protein sources, those should be inspected for beetles as well as the dry, grain based ingredients.

  • As an alternative to the current fumigants, carbon dioxide could be used to control flour beetles in foods. However, it needs some pretty high concentrations for at least 24h in order to be effective so it may not be cost effective yet unless it is an organic or high value commodity.

  • Caffeine gives them superpowers. (Okay, I’m exaggerating again.) Males who were fed caffeine courted females faster and mated with them faster. I really have no idea what this means from a control standpoint, I just thought it was cool.

  • Another randomly cool study: they like broccoli.

Don’t risk having to dispose of infested products or worse, a recall. Protect the site against flour beetles and other stored product pests that could be a risk. Whether you are producing flour or any other product that flour beetles can take advantage of, putting pest management plans in place is absolutely necessary. I am going to celebrate by baking something… maybe some chocolate chip cookies!


Oh, and contact us if you want help!


Lagniappe - bringing it all together: flour made with insects!


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