MSU Extension MI Ag Ideas to Grow With

Stored Grain Insect Pests and Their Lifecycles

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March 22, 2022

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The 2022 MI Ag Ideas to Grow With conference was held virtually, February 28-March 31, 2022. It was a month-long program encompassing many aspects of the agricultural industry and offering a full array of educational sessions for farmers and homeowners interested in food production and other agricultural endeavors.  More information can be found at: https://www.canr.msu.edu/miagideas/

  - Good morning. My name's Mike Staton and I work with MSU Extension. I'm a soybean educator, and I will be your host for this morning's session on Grain Storage and Safety. This slide is really important because this is our sponsors, GreenStone Farm Credit Services, North Central Sare. We're really fortunate to have these sponsors. Mark Wolbers, Alaska Pioneer Fruit Growers Association, thank you for your sponsorship of the program today, very, very important. With that, I'm gonna go ahead and introduce our first speaker, Samantha Daniels. And Samantha is an agricultural educator in Macomb County with an emphasis on insect management. Samantha, I'm gonna stop sharing and ask you to share your screen if you would. - Sounds great, thank you very much, Mike. Good morning, everyone. My name is Samantha Daniel. I am a field crop educator in Macomb County with a background in field crops entomology. And today during breakfast, I will be talking about Stored Grain Insect Pests. So, all the little beetles and larvae that get into the variety of stored grains. I'll talk a little bit about their ecology, their life cycles, and then briefly about their management. So, just a quick outline of today, I'll have an introduction, and then talk about the basically eight primary stored grain pests. We'll look at their identification, ecology, and life cycles. And I just wanna show this image here. So, this was actually a big glass jar of dog treats that my boyfriend and I had in our home, and we had forgotten about it. And one day I looked at it, and it was absolutely infested with these beetles. So, this is a drugstore beetle. These tend to be in like pantries and homes, not as much as in grain bins, but still, it's another stored grain insect. So, that was pretty gross, but pretty cool as well. So, I'm also gonna talk a little bit about preventative measures, management, and then summarize everything that we go through this morning. So, first off, let me just summarize a little bit, what is the impact of feeding damage from these insects? So, it can reduce grain weight, nutritional value, as well as the germination ability of the grain. And you can see here, the damage to this grain, all of the holes, the burrows, and the feeding damage, you can see how that is going to drastically reduce the weight and the nutritional value, and impact germination. There's also gonna be a big impact to quality issues. The grain can be considered contaminated. A lot of these insects could cause odor, and then mold and fungus is often associated with these insects. This here is some corn, and all of this webbing is actually from moth larvae that have left their webbing all over this corn. So, this is a serious infestation with all of that webbing, which you can imagine that, that's not something that we want to see. And all of this can lead to a lot of financial impact. And it is estimated that stored grain insect damage leads to about $2.5 billion a year in costs. So, that's a huge impact from these insects. So, the primary stored grain insects I'm gonna talk about today can be branched out into two broad categories based on how they feed. We have internal feeders, so, these are the ones where the immature, the larval stage, will burrow into the kernel, or the adult will actually lay the egg inside the kernel. And then we have... These are the examples of our internal feeders. So, we have the granary weevil, the rice weevil, the lesser grain borer, and the Angoumois grain moth. And you can see the larvae of each of these insects are inside the kernel. Then we have external feeders. These are the ones that are feeding on the grain dust or cracked kernels, any of the other materials that are inside the grain bin that comes from the actual grain itself. Whoops, went a little too fast there. So, that would include the Indian-meal moth, the sawtoothed grain beetle, the red flour beetle, and the cadelle beetle. So, let's look a little bit closer at weevils. So, we have our granary weevil and our rice weevil. I'm going to talk a little bit about identification, but I think it's important that if you find insects or any sign of insect damage in your stored grain, that you work with your local extension agent to really help to identify what you've got going on, 'cause a lot of these insects can look very, very similar. The difference between the granary weevil and rice weevil, you can see that the rice weevil has these light spots on its elytra, or the back, there's four of them. And the granary weevil is really more uniform in color. So, that's a good way to kind of discern these two beetles. Also, being weevils, they have this long snout-like projection coming off the face, and actually the mouth parts are at the very end of this snout. So, that can help you determine whether a beetle is a weevil or not. Now, both of these weevils are gonna have very similar life stages, or life cycles. It's gonna start off with egg. And then this is what the larvae look like. Again, these are gonna be inside of the grain. You're most likely not going to see these life stages unless you're breaking the grain open. The pupal stage. And then finally, you can see how small these weevils are. This is one of the weevils emerging from a grain of rice. So, it's good to just get an idea that the life stages of these insects, there's four life stages. They undergo what we call complete metamorphosis. They go from egg to several different instars of larvae, pupa, and then adult. Now, there's some differences between the two. With granary weevil, the adults live around seven to eight weeks, and they cannot fly. Whether or not an insect can fly is important because it kind of gives us some information on their ability to disperse or spread out, and go to different areas. Each female of these beetles can lay about 50 to 200 eggs in her lifetime, since they have a fairly short lifespan of seven to eight weeks. And then optimal conditions, meaning proper temperature and proper moisture levels. They can complete their life cycle from egg to adult in five weeks. Now, with the rice weevil, these guys can live for four to five months, and they can fly as well. Oftentimes, infestations from these weevils can start in the field even before harvests. Each female, because of the longer lifespan, each female can lay 300 to 400 eggs. And in optimal conditions, again, optimal temperature and moisture levels, they can complete their life cycle in as little 26 days. Another thing to keep in mind too is oftentimes with these stored grain pests, you might see the damage before you see the insect itself. And so, this is kind of what gives you an idea of what damage from these weevils looks like. This top-right image shows the actual beetles, and you can see the burrow holes in the grain. And down here in this image on the bottom-right, this is actually an x-ray image of wheat. And you can see the insects inside some of these grains. So, you can see that these are a serious pest if they get into the grain. All right, next, we're gonna talk a little bit about lesser grain borer. So, this beetle, you can tell definitely looks different from the weevils. It doesn't have that long snout, so that tells you there it's not a weevil. Also, if you look, this part of the head, this top part of the head, it kind of goes like... it kind of covers it like a helmet. So, that's kind of a defining characteristic of this beetle. Again, it goes through four life stages. It has these long, kind of elongate eggs, very small, that are laid on the surface of the grain, and then the larvae burrow into the grain. So, here's a larva that's inside the grain, so you can see how they're very small, and then they pupate inside the grain as well. So, it's important to note, too, that both adults and larvae can cause damage. It's not just the immature versions that are causing damage. And each female can lay up to 500 eggs in her lifetime. And then when the eggs are deposited, they're deposited either on the kernels or sometimes loose in frass, and frass is just basically insect poop. When insects are in, you know, wherever they're at, if they're in grain or wherever, and they're constantly eating, they're also constantly pooping everywhere. And so, that's another sign that you might have issues is if you see frass. The eggs generally will hatch between 5 and 32 days, obviously that is due to, what is the temperature? The temperature and the conditions are gonna determine when they hatch. And then larval development is 30 to 46 days with the pupal stage lasting about six to eight days, The adults will emerge within the kernel. They'll stay within the kernel for about three to five days, and then they basically chew and burrow their way out. So, this is a good image, and it shows all the little burrow holes from the adults that are coming out. Some of the smaller little holes are probably from the larvae burrowing in. And now, we're gonna talk a little bit about the Angoumois grain moth. This is our final internal feeder. This is a very small moth. The adult is kind of a silvery color with some brown, and some feathery scales on the wings. Again, it's gonna have four stages, egg, here's a larva inside of a kernel of corn, and then the pupa will also be within that kernel. So, these guys actually prefer damp grain, especially whole corn. With a lot of these insects, only, at least with the internal feeders, only one larva can develop within each kernel. But with these guys, if it's corn, a lot of times, two or even three larvae can fully develop inside one kernel. So, you can imagine that that's gonna have a big impact on corn. The adults are short-lived and they're non-feeding. The adults are not causing damage, it's just the larvae that cause damage. When they lay eggs, they actually lay the eggs in the crevices between the kernels of corn. And the females can lay anywhere between 80 to 200 in her lifetime. Once the larvae hatch, they bore into the kernel, and then they complete their development usually in about 30 to 40 days. Now, this is where it can get really impactful is, in normal outside, general conditions, these moths can have four to five generations per year, but in some heated warehouses, it's been recorded that they can have 10 to 12 generations per year. So, you can imagine that for having that many generations, we're getting a really, really high pest load in the grain. And here is some corn, and you can see all of these kernels that have little burrow holes in them. And some of the kernels have multiple burrow holes. You can tell that those are the kernels that supported more than just one larva. So, that's it for the internal feeders. We're gonna switch over now to some of our external feeders. First one is the Indian meal moth. Now, this moth is a very striking moth. So, those of us who are entomologists, we might even say it's a very pretty moth, although what it does to grain is not so pretty. But it's very striking and has a very kind of unique look. And again, four stages, eggs, and then the larva. You might actually see the larva of this moth since it's feeding externally. And then they pupate externally as well. So, this is one of the most commonly reported stored grain pests in the United States. And each female can lay 100 to 300 eggs, and those eggs are laid on the grain surface, usually in bunch of 1 to 30. The neonate, or a newly hatched larvae, are feeding on just the fine grain materials. And then often when they pupate, they'll pupate either on the grain surface or even on grain bin walls. So, this last picture here on the far right, that's what the pupa looks like. So, it's something that you might see on the grain or on the surface of the grain bin itself. These guys can complete their life cycle in 40 to 55 days, generally speaking, but in really optimal conditions, it can be in as little as 28 days. And unfortunately, the frass, once again, the poop from the larvae, and the copious webbing from the larvae can cause contamination. So, if we look here in this image here on the far bottom-left, these are some larvae, and all of that kind of small, little clumpy stuff right there, that's all the frass. So, you can see from these larvae eating the almonds, not only have they damaged the almonds, but they've also left behind their frass. And that frass is kind of clumped together because it's sticking to all the webbing they produce as well. So, you can see that that is definitely not something that we want in our grain. Right. Next, we have the sawtoothed grain beetle. So, this beetle is, again, kind of unique because it's kind of more long and cylindrical. And on the middle body section, there's like little, basically sawtooth on the edges. And that's kind of how you can tell what kind of beetle this is. Again, they're gonna have eggs, the larvae, and then the pupa. Again, you might see these die since they're feeding externally. But it's good to note they cannot attack whole undamaged grain. So, a lot of times, they might be associated with other grain insects that can attack the grain. So, then they come in afterwards and then start feeding on grain that's already been attacked. It's important to note that although they have fully developed wings, there's no record of adult flight from these. So, their dispersal is gonna be limited. And females can lay anywhere from 3 to 315 eggs in her lifetime. And they generally deposit them singly or in small masses. And in optimal conditions, they complete their life cycle in 25 days. These guys are somewhat cold resistant. So, sometimes, you know, cold... in areas where we have winters and whatnot, the cold will kill off a lot of these stored grain pests. But the sawtoothed grain beetle does have some resistance to that. Finally, this is an image of some grain that these guys have fed on. Once again, this would've been grain that was already damaged, and they've come in after the fact and done some feeding on that. Next is red flour beetle. So, the red flour beetle, once again, are very small insects, kind of a uniform reddish brown color. Their eggs are really small, kind of flat, oblong, strange shape. And the larvae here, this image shows the top. That's a newly hatched larva. And at the bottom, that's a later instar larva. So, you can see how the larvae really grow with these insects. And then the pupa is that final stage. So, again, these guys cannot attack whole undamaged grain. They're gonna be coming in after the fact, or they're gonna be attacking grain that was damaged in the harvest process. The adults can live over one year. So, the females can produce up to a thousand eggs during that lifetime. They also can fly. So, their dispersal, again, is gonna be a little different from those that cannot fly. One thing that's particularly bad with these is that their infestations can cause an unpleasant odor and taste in the grain. So, that's going to severely impact the quality of the grain, and whether or not it's saleable for full price. These guys are, however, most common in that Southern states. And here is a red flour beetle. You can see that the size of this insect, they're all very small. Next we have the cadelle beetle. So, the cadelle beetle is actually one of the largest stored grain insects. So, a good size, big, black beetle. It's about half an inch long. Again, they have eggs and then they have the larvae, and then the pupal stage. These guys, again, both adults and larvae can cause damage in grain with these beetles. The female, again, can live over one year and lay up to a thousand eggs. And the eggs, when they're laid, they're deposited in grain material, generally, in batches of 10 to 60. Once they have reached the final instar, or the last stage of the larval stage, they'll oftentimes bore into wood or any other material away from the grain to pupate. So, oftentimes, you're not going to see the pupa of these beetles. And here, we can see this image in the bottom left. There's an adult beetle with the larva here in the grain. And you can imagine that having those, you know, kind of a big, fat, white, grub-looking thing in the grain is not something that we wanna see. So, that's it for the feeders of grain. I also wanna talk briefly about fungus and mold feeders. So, we have the foreign grain beetle and the hairy fungus beetle. Again, you can see that a lot of these insects are very similar the way they look. And so, if you find any insects or any feeding damage in your stored grain, it's important to work with a specialist or with an extension educator, or your extension office, to really determine what type of insects are in the grain. But with these two, they actually do not cause any damage to the grain. They actually feed on fungi and molds that start to grow on the grain. So, these guys are, I guess, in a way, could be seen as beneficial as they are an indicator of moist storage conditions or moldy grain. So, if you have these guys, then you know that something's going on with the storage of the grain, and something needs to change. And these guys are also usually not the primary insect in infested bins. There's usually another actual internal or external feeder associated with their presence. So, what can you do to prevent these insects? There's a lot of things you can do, before binning, it's really cleanliness, cleaning all of your equipment used in harvesting and the transport of grain, and then cleaning the grain bins thoroughly, all surfaces, getting rid of the old grain dust, getting rid of anything that could harbor insects. It's also good to think about removing any debris and growing vegetation within 10 feet of bins. Again, anything that's sitting around the bins, any of that vegetation can harbor insects. And if you're planning on adding newly harvested grain to grain that's already stored, you might consider fumigating the old grain. And then if you're planning on storing the grain for greater than one year, it might be good to consider grain protectants. Now, after binning, there's a couple things you can do. So, inside your grain bin, you could top dress the grain with grain protectants, which are labels for application as surface treatments. Those can help with some of the insects that we just talked about. And then you could also hang No-Pest Strips in the open areas within the bin, which are just basically strips with insecticide on them, and those can help to control flying pests. Now, once you actually have any of these insects in the stored grain, there's some things you can do for management. So, really, once grain reaches 55 degrees Fahrenheit or higher, it should be inspected every two weeks. That's a good way to keep an eye on it, and see if an infestation is starting to ramp up. If there's insects present on the surface, that doesn't necessarily mean you have a serious infestation, so it's important to do some sampling, for example, using a grain probe, to really determine the extent of the infestation. It's also very important to identify the insects because we cannot manage them properly if we don't know what we're dealing with, especially if it's an internal feeder versus an external feeder, or maybe it's just one of the fungus feeders. So, identification is key. And grain is really considered a weevily only when internal feeders are present, that's kind of the term used when grain is often rejected, is its got internal feeders. So, there's some different management steps to take based on the type of feeders you have. If you have internal feeders, you've three options really. You can either feed the grain as is, if it's an animal feed, you could sell it at a discounted rate, or you can fumigate. Fumigation though requires special certification because it is highly hazardous to the user. It also has no residual effect. Once the the fumes basically from the fumigation have dissipated out of the bin, usually within about 72 hours, there's no more effect and that grain is immediately susceptible again. So, fumigation is an option, but it needs to be carefully considered. Now, with external feeders, surface feeders like the Indian meal moth, that's where you can use a top dress and that can help to control those surface feeders who are only in like the top five to six inches of the grain. Those secondary feeders, like the sawtoothed grain beetle, the red flour beetle, and the cadelle beetle, a lot of times, you could run the grain through a cleaner or aspirator that will kind of clean up some of those dusts and some broken kernels. And a lot of times, we'll remove the adult beetles, it'll just clean it out, but if you have internal feeders that are also present, your only option really is to fumigate in that case. So, finally, I'm just gonna quickly summarize what we talked about. So, basically, stored product insects can cause significant damage to a variety of grains, to everything from wheat, corn, oats, barley, sorghum. A lot of these insects are also pantry pests. They just have a lot of host foods that they'll feed on. The most significant of these insects are adults and larvae of beetles in the order Coleoptera and then adult moths... Or it's actually, yeah, larval moths in the order Lepidoptera. The insects can be grouped into two main categories. They're either internal feeders or external feeders, and determining which you have is important in management. So, proper binning techniques and waste material management is critical in preventing infestations. Oh, oh, oh. And control of existing infestations is reliant on proper identification of the insect or insects present. A lot of times, control may not even be required depending on what's going on. It may be something that is simply just different storage techniques or what. So, it's really important to work with your local extension agent on this. And with that, I can take any questions. - [Mike] We do have time for a question if there's any questions from the audience. There was none entered into the Q&A. We did have a question, Samantha, about, do the insect's bodies or the insect's frass, is there any kind of toxins associated with them at all if there is infested grain? - You know, not really in toxins, but it can just lead to odor, and just a bad taste. It can cause problems with taste in the grain. But I don't think there's any like actual toxins per se, it's more about like just a contamination and just a reduce in quality. It's not necessarily going to be detrimental to, as far as like, you know, feeding to animals, generally speaking. There may be some examples of that or exclusion to that, but I didn't see anything in the literature that said that anything was toxic. - Good, that's good news. The other question that we had gotten or received was you'd mentioned that there are some critters that will feed on molds and fungi on the grain, but is there kind of a chicken and an egg thing, could insect feeding make the grain more susceptible to molding and toxins to develop? - Absolutely. Absolutely. If we have some of those primary feeders that are feeding on the grain, then yeah, it can definitely open the door to have different types of molds and fungus growing on the grain. And then that's also going to attract those mold feeders, which is why a lot of times, those mold beetles, the fungus beetles, are not gonna be the only thing in the grain. A lot of times, if you have those, you're gonna have a primary feeder in the grain as well. - Very good. Very good presentation, Samantha, thank you very much for this. It was a lot of good information, a lot of good pictures showing us what things look like, life cycle descriptions, and management topics. So, thank you very much. - Great.