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Mealworm Pupation Issue and Mass Cricket Die-offs.

Let me introduce what going on. I breed lots of insects, especially roaches since they‘re easy and hardy. I feed my insects potatoes bought from a bodega, sometimes carrots or sweet potatoes. For the mealworms and other darkling beetles I use what bran as their substrate, and the mealworms and superworms have a bunch of styrofoam too. I usually don’t use a substrate for crickets or roaches, making cleanup easier and easier to see the insects. I started breeding crickets and mealworms with carrots and my first batch of mealworms we’re doing great and I got maybe a hundred or so beetles and a few deformed ones sometimes, but it wasn’t a problem. The crickets didn’t seem to ever do any good, with or without vermiculite and within a week or two most died off. I didn’t clean the containers often but even doing it seemed to not help. This was in August, September, October, November 2018.

Now, the second generation of mealworms, very plentiful, along with the subsequent batches have almost NEVER pupate correctly. They always either slowly turned brown, were almost stuck in their shell even though they locked ready to hatch, or (very rarely) hatch correctly. Even with higher humidity, lower humidity, winter temperatures a bit below room temperature, summer temperatures a bit above room temp, in their own separate pupation chambers, clustered together, left alone, and with or without Substrate to pupate on, maybe 2 or 3 out of a few hundred in the last several months since late autumn 2018 all the way to now in July. They also are pretty slow and don’t move much, though that might be since they’re getting ready to pupate so I don’t know. The issue seemed to coincide with feeding them potatoes instead of carrots (I did it since potatoes are larger with a larger surface area, keep moisture well enough, and much easier to cut). They are getting to pupation stage, so clustering of mealworms doesn’t prevent pupation like the superworms, but they all develop incorrectly and die. At first I thought it could be humidity, but it hasn’t changed even as the temperature increased or I put them in a wet bin with paper towels. I have a suspect feeling it could be pesticides in the potatoes I‘m feeding them, though I haven’t found info on this issue. I hear potatoes absorb lots of pesticides, so maybe they could impede development. This could explain the issues I’m facing with all my cricket batches too, since I feed them the same vegetables. First I did house crickets, in vermiculite and then ~1000 in a 55 gal tank with no substrate but they all died off the same way in a shorter period of time than my first batch in Ate July 2018. I used to think they died off from disease but now I’m not so sure since this is much much more regular die offs that what I hear in the breeding community. In fact, I ordered a substantial batch of banded field crickets (known for disease resistance and hardiness) and probably 60% or more died (~150) in less than 4 days and I cleaned it out but they kept dying. (~2 weeks later there’s like 5 left and one is female, the crickets kept on eating their fallen brethren which could transmit disease if it were that. I bought my crickets at petsmart first and then only online from Flukers or Josh’s Frogs, the mealworms and supereorms from petsmart and petco respectively. The crickets also get gutload powder and water gels, but that doesn’t happen for my mealworms. I am now feeding them organic potatoes and sometimes organic carrots to the minimize the risk. I keep my mealworms in a dry substrate in a slightly cooled room in darkness, while my crickets and roaches in a hot attic (~90F). The water dries fast in the attic, but I don’t think desiccation is the problem since mealworms are commonly in dry substrate and don’t need much water. The crickets used to be in a room temperature room with adaquate water. No I don’t think the wheat bran is the issue, though I did introduce it after mixing it with a moldy oatmeal Substrate populated with lots of baby mealworms who hatched from eggs last year and used it from there without the oats except in one container, so it really shouldn’t be that.

When it comes to my superworms, they have taken pretty long to get to pupation since I don’t know when to isolate them for pupation so I have a few that I randomly chose to isolate and probably 5/8 of them pupated correctly, with one that went the same way as the mealworms and two that hatched with a deformed abdomen and couldn’t walk or run from their hungry and healthy peers who gutted them for scraps. They are doing great eating their styrofoam but they mix the substrate with the foam and that obviously reduced the viability of the frass for use in plants or composting, so I don’t know how to deal with that. My micro mealworms (a smaller version of mealworms, known to be probably a moderately toxic larva and quite toxic beetle for their quinones (similar to millipedes)) have seemed to bounce back from some mild issues to a decent small culture, they did have the same pupation error at some point but they seem to be doing fine now though I still fed them the same bodega potatoes and now the organic ones. My lesser mealworms (black cleaner beetles, cleaner crews, etc.) are thriving but they ruin their wheat bran substrate by turning it brown and making it smell like ammonia and vomit, and turning the potatoes into brown mush, but they don’t seem to mind and never had pupation issues to my knowledge.

When it comes to the roaches though, they seem to be doing just fine, which would make a lot of sense since roaches are known for easily and rapidly developing pesticide resistances within as little as one generation. I have many roaches all of which are living fairly well, but my lobster roaches die off semi-regularly, and my Madagascan hissers and discoid roaches have either had one litter or none at all even though they‘ve been going strong for a few months. I’m actually still feeding them the non-organic potatoes since they don’t have any major issues, maybe I should feed my hissers and dicoids the organic ones though..

If you have any idea as to why this may be happening and/or how to fix or at least help this issue that would mean a lot. I‘m a fairly new breeder, almost a year now, still expanding my arsenal and I don’t see myself stopping soon and now I catch wild insects for different cultures, pillbugs being a staple for that hobby though they‘re not insects and probably don’t taste amazing since they eat wood and decaying matter. I do eventually plan to eat these (as a diet staple, like farming my own food) and/or sell these insects at some point once they get large enough in their culture sizes to get good amounts and even to sell, so tell me if potato beetles (micro mealworms), lesser mealworms (black cleaner beetles), greenhouse millipedes, or narceus americannus-annularis (giant American millipedes) are toxic or not the best idea to eat so I know for sure if I get adventurous. I haven’t seen specific info on eating greenhouse millipedes or black cleaner beetles, but I take it millipedes might not be the safest arthropod to eat, but they‘re much easier to breed than centipedes (a bit gross, mostly top-dog carnivores who also cannibalize weaker brethren too) so I still want to have them at least for fun.


  • Hi Richard22, - As regards mealworm pupa from larvae fed potato: agricultural products to control potato beetles (ex: brand Novodor) have Bacillus thuringensis (“Bt”). As the Bt spores germinate inside larvae they cause all kinds of problems; one being septicemia & a visible clue of this (septicemia) is that as young bug ages it’s insides turn dark (“black”). Bt also interferes with bugs’ hormonal segue, so get kinds of developmental defects in emerging progeny.

    I did read your full comment, but unsure what else to address. I don’t rear most of those bugs.

  • edited July 20

    Fungus seems plausible, though from what I've seen my mealworms don't have issues until pupal stage and don't grow mold or turn black until long after they die at pupation (if ever, only some turn black or grow mold). If those are the telltale signs of fungi killing them then I don't know if it would be blocking the growth of the pupa. It also seems quite rare for the larva to turn black, and I have never seen mold grow on them. Pesticides just seems more plausible to me, because they are absorbed through the root vegetable (infact potatoes have around ~34 different ones) and obviously pesticides wouldn't be good for insects (though I don't know if it'd be negligible).

    Could pesticides absorbed through the soil into the potatoes cause any issues? I wonder because both the crickets and mealworms aren't living very long, so I think it'd be more likely to affect both insects, but not the roaches because they could easily develop immunities, especially after one generation as they are known for doing that. The one commonality between most of my staple insects is potatoes, so maybe the fungus (or pesticides) cause(s) widespread and gradual pupa death in mealworms and rapid mass-death in crickets (seems like they twitch until death, though I don't think the viruses would be the issue because this has happened with EVERY cricket colony I've done), but something keeps the roaches from having issues for the most part (I don't know if the roaches could be immune to fungus, pesticide immunity seems more plausible). I notice some smaller and newer roach cultures are dying off more than the established ones (maybe ~2 out of 15 new horseshoe crab roach NYMPHS die off within 1-2 weeks of starting the culture after being fed potatoes, Flukers cricked gutloading food, water gels, and a water pillow) , so I think there is an immunity they build up over time and after generations. I don't think the flukers food could be an issue because it is made for the insects and I don't feed it to the mealworms obviously, sometimes it does get infested with grain mites but I can tell by the smell quickly.

    If potatoes are the issue (whether it be from pesticides or fungi), should I use organic potatoes or use carrots (or an alternative)? I think I will try mealworms ONLY on carrots again and see what happens (if nothing changes then I think it'd have to be pesticides since potatoes and carrots are both root vegetables and fungus being in both potatoes AND organic carrots doesn't seem plausible to me). I don't use apples because they turn gooey instead of drying out. I am starting to use a lettuce salad mix instead of potatoes for my new roaches, so I think that'd be a good idea. I am not so sure about the mealworms though, lettuce would get messy and carrots don't have much surface area in a large 'field' of wheat bran.

  • Bt is a very common “natural” concept insect control tactic that is added into several commercial “pesticides” ; and to be shelf viable it is mostly in a dormant stage. It is not like a fungus root crops might pick up by growing in soil & it will then go on to multiply on the outside of an insect.

    My tactic would be to experiment without feeding bugs the potatoes available in your area. So am in agreement with you that it is worth trying carrots instead.

  • That makes sense, here is some more context. I am currently breeding in the suburban-ish outskirts of Baltimore City Baltimore Maryland, and I used to buy the potatoes at a bodega but now from Giant and Wholefoods, and of course it’s mid-summer.

    I have and am executing one last resort to try to figure this out; at the moment I am now making experiments, five small mealworm cultures with carrots, organic carrots, organic potatoes, collard greens, and banana peels, and I am doing 3 ones for crickets, organic potatoes, organic carrots, and collard greens, and maybe collard greens later. Considering I literally cannot find ANYTHING regarding this theory of pesticides killing farmed insects on the internet, pesticides or insecticidal fungi, the most logical step is to take this in my own hands and try different vegetables to feed them, and I will also give the crickets cut up sponge pieces for moisture and egg laying instead of water crystals because they are expensive and seem to disappear quickly in my hot attic where I breed all my roaches and crickets. I hope 95-103F is not too hot for efficient breeding because that’s just how it will be for the rest of the summer. There is good ventilation there and humidity is decent, but the crickets and tropical roaches might need higher humidity though I cannot accommodate that because doing so would require buying a humidifier and regulator (alienating the roaches/camel crickets that prefer moderate humidity), or reduce ventilation in the bins which facilitates molds of all sort. Feeling pretty alienated having such monumental failure but nowhere providing an answer, Google or whatever.

    I’ll update this soon, maybe within a month; at least one time, and document the results. If the results make no difference, either all the root vegetables fed to the crickets have sufficient levels of pesticides (and the mealworms fed on collard greens and banana peels survive pupation), or some other implausible external factor is affecting the results in a way untypical of normal breeding. I have one control group for the mealworms, normal giant russet potatoes, and I will compare the number of dead pupa to the rest.

    One last question, should I put the pupa in a container with some substrate or just put them on a lid (to keep mealworms from eating them, which I have noticed happens) in the same mealworm container, or even bother putting the pupa in separate, wide or small, container just for the pupa? Whatever is best for a success ratio would be nice to hear.

  • If this is any use, it’s pretty long and complex on the mealworm immune system, here is a document:

  • Update regarding small roach cultures: after feeding horseshoe crab roaches and giant lobster roaches celery, many of the horseshoe crab roaches died and maybe 6 of 9 giant lobster roaches died, within three days of feeding them celery. Only 2 of the former and 3 of latter remain, in fact I started with 11 of the former and ~15 of the latter, feeding them vegetables other than organic potatoes have massacred them. Also, a Culture of wild caught oriental roaches have died in the dozens since feeding them leafy greens since a few weeks. If this isn’t pesticides, I don’t know what it is. I am utterly baffled just switching the vegetables would make these roaches drop like flies. A website even claims that celery is a good vegetable to feed dubia roaches, which is probably akin to telling people to feed poison to their farm animals. NEVER FEED INSECTS CELERY. This is an utter travesty, now I have to either get sympathy from the roach breeding site or buy another 60$ of roaches to try it all again, risking them all dying just from feeding them certain vegetables.


  • You could try ditching the fresh veg all together. The crickets and roaches should do ok on dry feed and water crystals. If you're breeding lots then organic table poultry feed or chick crumbs would be cheaper than the flukers feed and a chick drinker would last longer before it need changing than the water crystals.

    Not sure if you mentioned humidity but if it's over 60% for the crickets then that could be causing you issues as well - they benefit from good ventilation.

  • Would they lose nutritional value, or lower the likelihood of surviving to breeding age, if I skipped vegetables? My crickets were in a sterilite plastic bin with decent sized netting on the lid in front of a fan in a hot attic. Now, my experimental batches are located in a warm bedroom, which I think is pretty humid. Why would humidity affect the cricket lifespan? I though they and most roaches liked tropical conditions

  • Diet does affect the nutritional composition of the crickets, but I'm not sure to what extent. From my experience survival rate on a grain based, dry food is high providing the particle size of the feed is kept fairly small (they can't cope with whole grains) and water is provided. A poultry starter feed gives good FCR due to higher protein levels. If you're gut loading them then you might something with more calcium etc.

    I think the main issue with high humidity/poor ventilation is that it supports the growth of pathogens that harm the insects. Fungal issues are normally due to humidity. Perhaps in the wild lower population densities mean that disease outbreak is less of a problem.

  • edited July 30

    I have taken the tests. The same death rate happens for 31 crickets fed organic potatoes as the non produce ones. Either viruses are in each batch, or the pesticides killed the first batches and then fumes from the dying ones lying in an exposed plastic container in an unventilated room (also pretty humid) killed the non-produce ones. I’ll use Ocram’s Razor for this, and from this I’ll succumb to the sad reality that starting cricket colonies is very very hit or miss, like a Petsmart employee said to me. I will try this again in optimal conditions and also with banded crickets (only for science, because I have almost lost hope in breeding common feeder crickets), but my field crickets are thriving, no random deaths whatsoever, telling me it is probably not pesticides and is probably the feeder crickets’ susceptibility to virus and/or the supplier’s negligence or something. No wild contact with virus tells me the issue is the supplier and not just my uncleanliness. I also house my field crickets in my hot but airy attic, room humidity and hovers around 90-97F most days, while my experimental batches are in my humid-feeling and barely ventilated unused bedroom with the dead ones on-top of the critter keepers. Supposedly, many batches of crickets die off, 1/2 or something like 3/5; only some actually get breeding. Then, it’s a matter of cleanliness and caution to keep viruses from getting in. What I have learned time and time again is that feeder cricket breeding sucks, and roaches are objectively better. It’s only a matter of time before I try sautéing a Madagascan hisser instead of a house cricket, along with some striped ground crickets and fall field crickets in there too. I have heard roaches might have uric acid, is that true for all roaches and are there any other strings attached to eating roaches instead of feeder crickets? I doubt many of you actually tried cooking a roach just like a cricket and not eating as a dare, so I must be a minority actually considering this.

    I can easily get a few dozen striped ground crickets with my bug net sweeping through some tall grass in my local park at midnight, including some grasshoppers and fall field crickets. Sure they’re small but the more the merrier and the faster I can start a big colony of those guys. They jump around a lot but I got some really nice photos of them on my camera. I can't for some reason get the photos to display within this site unless I use my iPad's camera right in the moment, so you'll have to click the links, which of course means no one will click it but whatever its better than no one seeing the images. (striped ground cricket) (adult striped ground cricket) (left to right: black field cricket; Japanese burrowing cricket; striped ground cricket)

    **Questions: **

    Are viruses as much of a problem after the first generation of common feeder crickets?

    Are wild field crickets any worse than feeder ones, after breeding the 2nd generation? I hear house crickets are the only easily sellable and marketable cricket, so they seems bleak for non-personal use, but it’s so much easier keeping them alive, I also have 4 sizes so it is more customizable.

    Are crickets genetically modified to die off or be infertile? Like giant mealworms, wax worms, hornworms, or butterworms. I hear some pest species are made to not be fertile or die before getting to breeding age, especially butterworms (they're from Chile and are pests), but I experienced a hard time breeding wax worms, but eventually a few waxworms did spawn from the first generation and they all laid many many eggs and now the waxworms are making cocoons and are thriving. I also had a hard time breeding hornworms on their normal chow feed (they are very likely rendered infertile as they are heavy-duty pests), only 2 moths made it and they didn't get blood circulated so they died, not an issue as hornworms are pretty gross anyway; I hear they taste like briny tomato (unless in a gourmet meal, not trying it). I mean it makes sense, economically and morally as they want to ensure you have to keep buying their supplies for a constant subscription service of income to them and also keep the pests from being released by accident by amateur breeders. Could the same be with mealworms? Is Petsmart even a good place to buy insects to use as breeders? I bet I'm sounding like a quack at this point but I think its plausible some feeders are prevented from being fertile.

  • @Richard22 this is a tough and demoralizing situation! I can share some of our experience with crickets & mealworms that may be helpful.

    Water crystals are generally not good for long term colony maintenance, intended for short term storage of live feeders before being fed to pet herps. You can use a tray of wet coconut coir which holds moisture well and resists mold/fungus growth. You may have to replenish moisture daily depending on the heat and relative humidity.

    95f is hot for commercial crickets, especially acheta domesticus, these prefer <90F. gryllodes sigillatus are more resilient to higher heat, but also require higher humidity, and >100F can cause lethal stress, even for only few hours or a day.

    Twitching around time of death is a symptom of acheta densovirus, particularly if you see them on their backs twitching. If you have at some point had infected crickets you may not be able to grow achetas in the same habitats/area with expensive measures (extensive sanitation, new bins, and possibly treating the room with ozone). Gryllodes sigillatus are generally not thought to be susceptible to the acheta densovirus but certainly are susceptible to other pathogens.

    I would recommend avoiding pet stores for initial stock and order directly from breeders online like Fluker's Farms for Acheta crickets, Top Hat for gryllodes sigillatus, and various breeders for mealworms (try to find as local as possible). However shipping live insects in the high heat of summer can be a significant stress, and most suppliers have heat/weather warnings around when they can ship orders. It is also important to receive the package immediately and avoid the box sitting in a hot doorway.

    Mealworms can be grown without any supplemental moisture if the ambient humidity is kept up, mealworms generally thrive in very high humidity, as high as 80%RH, but we have had success at 60%+/- However they mature more slowly without supplemental moisture.

  • edited August 1

    Thanks for the advice, I’ll try another 2 or 3 cricket ‘trials’ as experiments and see if a difference in death rate occurs. I’ll look for less chain breeders for the house crickets and mealworms, while banded ones I’ll get online or maybe craigslist or something. My attic might be a bit too hot, but my unused bedroom is ~87F at 50% humidity but being there for a few minutes makes a good bit of sweat, I’ll need a room fan like in my attic in there. I don’t use water gels anymore, they are expensive and dry out into tiny crumbs so now I just use sponges. They dry out within a day so they don’t have water half the time unfortunately and I can’t remember to constantly hydrate the sponges. I have the current results in this photo: image

    Vermiculite, ecoearth, or no substrate? Currently using vermiculite in the trials.

  • @Richard22 are you you referring to substrate in the bottom of the bin? we generally do not provide a base substrate beneath main substrate structure (egg carton/cardboard partition/etc.) but you could spread a thin layer of dry feed on the bottom of a bin if using standard sterilite type bins that have a groove around the edge where crickets can get stuck when they are younger

  • I heard the substrate might absorb smell and keep frass, but the substrate doesn’t really matter to me.

    I think I have come to a conclusion about the pupation issue after seeing a few posts about deformed beetles, the reason they turn brown is probably humidity and the reason many of the surviving ones don’t hatch correctly is very likely how I treat the pupae when relocating. The pupa in my unventilated experiments where I leave the pupae are not turning brown, but some are deformed. I still don’t fully understand the pupae turning brown issue because I’d imagine most people who breed mealworms don’t put the pupa in an unventilated and regularly moist container and this issue isn’t brought up, so it’s still up in the air. I also may isolate the pupae like my superworms who have the same issue but don’t turn brown and mostly pupate correctly, I generally find the larvae and isolate them before pupation so it’d make sense they would be less disturbed and since they would be fully isolated. I normally lightly pick up my pupae and put them onto a thin layer of wheat bran with the others, I also don’t clump them up but instead distribute them across the surface. My pupae are normally in an open container at room temp and humidity, normally around 78F-84F, I also don’t isolate them like superworms but that never was an issue for the successful batch a year ago. I bought my mealworms all from Petsmart due to the convenience, but there are a few more options around my area and online vendors. Another forum said I should isolate the pupae, but to me it’s incredibly impractical for mealworms and never mentioned as important for normal mealworms, so I assume it’s not important.

    Is humidity and lack of disturbance this monumentally crucial to the success of mealworm cultures that no online tutorials would mention this huge vulnerability? Could certain vendors be doing this? I did get a successful batch from Petsmart a year ago, but their offspring had the drying out issue across the board, so I am unsure if its the vendor or the conditions and pupae treatment.

    What is the proper environmental conditions and treatment for the pupae so they don’t dry out or fail to hatch from their skin?

  • Hi Richard22, - Regarding mealworm pupae: I am uncertain what “unventilated” means in your discussion. What comes to mind for me is that they need to exchange gasses, they are passive to our eyes but metabolizing while metamorphize & need to “gas” out.

  • edited August 11

    See free full text on-line of “Tracheal compression in pupae of the beetle Zophobas Morio” & I suggest initially just go to it’s last section “Discussion”; 2nd paragraph’s 2nd sentence.

    To get rid of metabolic CO2 (control cellular pH) pupae need to open a spiracle. If your pupae are kept both “unventilated” plus at the same time “moist” then water vapor may be condensing inside the spiracle impeding (reducing space/pressurizing against) pupal abdominal pumping away of CO2.

    Just observing pupal abdominal motion is not an indicator gas is going out. Since, as determined in report cited, spiracles may be closed (for abdominal pumping force being directed internally) while pupae are slow to react. If this is so they may be successfully completing relatively too much internal pumping (spiracle closed) in relation to partially completed CO2 pumping out (while spiracle open) and the unbalanced CO2 inside messes with cellular functions by distorting pH; which would skew hormones.

  • When there is ventilation, their wings turn dark red and eventually they turn brown (likely drying out), when they’re in a humid container they seemed to only have the failure to pupate into beetles issue where they limp and starve to death oand/or get eaten. I have a few cultures in unventilated bins (since I neglected to cut the lid and install netting) and I haven’t removed the pupa and already 2 beetles have come out of 31 mealworms already, though a few deformed ones and drying out ones are there. Remember nearly every pupa would have their wings turn red instead of their appendages after some time pupating, but it seems with a closed lid things seem to be better. I can’t seem to use an image to show without taking a new one, so I can’t show them right now.

    My striped ground cricket colony has suffered heavy losses randomly, I had forgotten to feed and water one day and then I skipped another day, 5 days with the same potatoes and water. They are right in my hot attic, the temp fluctuates from ~87F-99F+ depending on the day, and they are in front of a large fan, their bin is a large sterilite bin with netted ventilation on some of the lid. They have ecoearth, sponges, dry food, forest moss, some egg cartons and potatoes. Within probably a day everything except the sponge dries out in the heat, normally I fix that every other day. My larger field cricket kritter keeper bin with the same stuff but mostly larger crickets is doing fine, though I didn’t forget to tend to their needs that day.

    Could densovirus or other diseases affect local crickets too? I hear it only affects acheta domestica, perhaps it’s my negligence to tend to them for a few days with water or less likely the Flukers gutload powder or something else. It’s hard to have high humidity AND heat when the conditions must affect my whole attic, anything too humid would be unbearable every other day for 30 mins. I guess I could try a large cabinet with a humidifier in part of my attic, I don’t know.

  • Hi, - I have poor internet connection now.

    See excellent picture sequence of Fig.2 which deals with sequence you mention: pre-ecdysis, ecdysis & post-ecdysis. It is in Section 2.2 of free full on-line text of “Functional analysis of four neuropeptides ... in adult ecdysis of the red flour beetle ....”

    Also look at pictured timeline in Fig.4. Section 2.3 of cited report goes into 3 kinds of lethality: arrest pre-ecdysis, arrest ecdysis & post-ecdysis deficiency.

    Authors discuss neuro-peptide “bursicon” signal aberration in regards to wings.

    I am having trouble understanding what you are doing tactically with mealworm pupae. If you are not giving them a way to get rid of “enough/timely” metabolic CO2 then possibly some (most?) are losing synchronization of some of the neuro-peptides cited.

    I am not talking about genetic defects or dietary insults (unless pesticides ingested, which skew big hormones). My inference here is that the pupae are reacting unusual for you because of induced (poor CO2 venting) reductions of essential RNA at key time(s).

  • edited August 12

    So ventilation is a must, next step is figuring out if humidity needs to be high for pupa, because these ones aren’t doing so well. Even when I provide open ventilation, this browning of the wings and then the entire body happens every single time for each pupa and they all die. I am saying it seems to be less of an issue when I made the enclosure humid, but they still pupate deformed anyway. The results on google say the larva didn’t get enough moisture before pupation, but I still gave them large surface area potatoes most of the time. My temps are room temp and humidity since they supposedly don’t need higher temps to breed, but I am a bit skeptical now. image image The row on the bottom is of the browning pupae, the main issue which seemingly dries out every pupa, the general gradient is from left to right. The top two are the healthy ones, note the one on the top with the red appendages, it will probably pupate correctly at this rate. The one on the top right is the deformed beetle type, it barely limps around and has a very empty abdomen and the wings have not developed correctly.

    Here is a typical tray culture I tried, every pupa died the same way even though the tray method is supposed to be the best small scale method. Every mealworm I have done has been from Petsmart, maybe I should try another vendor. But at the same time this issue didn’t arise last summer when I started the worms, from Petsmart, but arised after the first generation and ongoing, almost ruling out the possibility in my eyes. Season is unlikely, since it’s been an issue through last Autumn all the way up until the current summer. image

    I also thought I’d mention some of my worms are growing beyond normal size of ~200mg, some are getting up to ~330mg. The remaining tray mealworms are this size. They don’t look like giant mealworms, but they might be a bad sign. I heard the full sized mealworms don’t get past ~250mg. image

    Here is a related unresolved post on another site regarding this issue: People seem to either say it’s dehydration or they don’t know, but I don’t know how they would be so dehydrated if raised very normally to other people who successfully breed them.

  • edited August 12

    Thanks for pictures. As far back as mid-1960s German mealworm colony issues prompted investigation that I think relates to you.

    Reportedly 30 - 60 % of an otherwise healthy mealworm colony can be carriers of gametocysts, plasmodia, vegetative cells & spore/sporoblast containing cysts. These are related to fungus, Protozoa &/or micro-sporidia.

    These can display phases of disease “zooitc” cycles. The colony can be tranquil in an en-zootic period & otherwise have epi-zooitic outbreaks.

    A lot of that old research is published in German so I can’t follow it. But the different zooitc entities seem to be found secure in either/or larval, pupal & adult fat bodies.

    Outbreaks are exasperated by cannibalism when either larva or adults feed on either infected larvae or infected pupae. Large mixed-age colonies in bins would apparently be more vulnerable.

    [[Bin colonies are not my tactic. I rear limited age mate larvae in openbugfarm grow bags, when cull late instar larvae the pupae separated out go into bran for “hatching” & then separated adults then get put into breeding/egg laying set-up. There is minimal situational opportunity for cannibalism (a few beetles still emerge with wing issues).]]

    I will relate that the researched diseases were (are) definitely reported as being sometimes spread by handling. Other vectors specified are mites, contaminated food (Microsporidia can live in grain) & even from other insects.

    You work with a lot of different insects and collect wild specimens. Yet presumably not absolutely sure if bringing inside anything else (ex: mites or spores).

    Rather than consider your commercial source of mealworms as problematic (since these producers are successful) maybe the issues occurring are from cross-contamination (ex: wild insect & inadvertent worker transfer).

    Since I don’t rear crickets have glossed over your cricket issues. If you have cricket developmental episodes then again consider inadvertent cross-contamination. Bugs in the wild certainly live alongside one another, but in low density colonies.

  • I don’t clean my gloves very often, perhaps that could be an issue. I don’t know if grain mites could get in every colony and cause problems, I rarely can see the grain mites but generally they’re on the produce clumped up or wandering in the feces of the beetle colonies. I neglect to kill the mite infested produce immediately as I should, leaving it all in a container full of rotting potatoes that eventually gets dumped into my horrible failure of a compost bin which is akin to sewer sludge, same smell and consistency. I could try using diluted eucalyptol on my gloves and rotting potatoes, but it would surely kill the springtails and millipedes, if not other insects. My gloves are somewhat thin, not gardening gloves, more like cheap household cleaning gloves.

    What else should I consider preventing the infections or what could be causing this issue? To me there is little I can do to prevent this, and I am considering abandoning the idea of breeding yellow mealworms soon, nothing I try prevents this inevitability. Crickets are a different story, they appear to randomly die off but some larger ones have laid eggs already in my critter keeper and none have died as of yet.

    My superworms are hit or miss when pupating, recently more have pupated incorrectly, but none have ever turned brown like the mealworms. Over the last couple months I have accumulated maybe 6 or 7 beetles from my styrofoam and bran medium-sized culture. My peanut mealworms have seemingly done alright, sometimes having the browning issue but there are cycles of beetles and larva though a mite infestation occurred in the feces. My buffalo beetles have flourished in the open tall jar I contain them in, even with a lot of feces, they have rarely had visible issues pupating.

  • Insect breeders are isolating their colonies & it seems you have a lot of potential interchange.

    As for mealworms only: I would consider current herd as being too suspect of being compromised to be worth trying to breed. Since mealies are relatively easy to get why not work out a safer protocol going forward, clean your dedicated space & start again with a few larvae.

    I never bred super worms (or peanut mealworms) so haven’t investigated them. If, as you say, there is “hit or miss ... pupated incorrectly ...” there may be some latent en-zooitic disease showing. The issue of whether getting brown, or not getting brown, (in comparison to yellow mealworm pupae browning) may be just because different infestations are provoking some of the pupation issues you see. However, I am in no position to say whether there is definitely a zootic problem developing.

  • What then should I do if the plan fails, as it most likely will considering the low likelihood just my gloves or the wheat bran would transfer disease. Why is my problem so unique? If it kills every mealworm across multiple batches across different seasons and conditions with or without an enclosed container, should I just clean my gloves and this will stop? I highly doubt it. I’ll try at least one more time, oats as substrate, organic carrots or sponge as moisture, and I will clean my gloves beforehand and it will be in my hot attic. If it doesn’t work, I see no point in trying anymore. I’d be better off breeding the 7mg lesser mealworms in a huge jar and use ten thousand for a serving. Mealworms, supposedly the easiest feeder to breed, have pretty much defeated me. I’ll probably have more success with my Bess beetles in my vivariums, they’re known for being hard to breed.


    Older batch attempt, massive failure.

    These are my current test runs, 31 mealworms each, Silloh Farm coarse wheat bran and the produce of choice.


    Banana peel trial


    Organic potato trial


    Collard green trial, note the 2 beetles. I never replaced the first collard greens I added, so the moisture couldn’t have played a part.


    Large carrot trial, note the 3 beetles.


    Organic carrot trial, note the 1 beetle, less than the non-organic ones, but less surface area.


    Bonus control trial with normal large potatoes.

    This might be a bit out there, but maybe it’s the wheat bran. Hear me out, I switched to wheat bran after hearing it is probably easier to digest than large oats like oatmeal and would be more convenient than coffee grinding it into a powder, though it was not at my local supermarkets except Whole Foods. At the same time was the immergence of the pupation issue following the adding of wheat bran to my first hatched-from-egg generation, which was in grey moldy oats, but that didn’t seem to matter. I bought wheat bran online and then from Whole Foods under the name Silloh Farms Coarse Wheat Bran. I will try a new batch in oatmeal and another in ground oatmeal, same conditions but I’ll feed them the large carrots since it might have played a part in the 3 beetles.

    So far, I have had around 180 mealworms, split into 31 for 6 cultures. Banana one has 5 dead pupae and two looking like they’ll die. Organic potato one has two dying and 2 dead pupae and two dead mealworms. Collard green one has 6 dying and two dead pupa, 2 dead mealworms, and 2 beetles. Non-organic carrot one has ~2 dead and 5 dying pupa, two dead mealworms, and 3 beetles. Organic carrot one has at least 5 dead and 3 dying ones, one dead mealworm, and one beetle and one slightly deformed beetle. Non-organic potato one has 1 dead and 3 dying pupae and two dead mealworms. Two of the dead pupa have grey splotches that look like it could be disease. Two dying pupa have a dark red splotch, this sign was more common a while ago.

  • My cellphone is cutting off your sentences & the long comments tricky to sort out.

    To my way of thinking your multiple insect ventures cross contaminated your yellow T. monitor mealworm colony by the time you started getting unusual developmental problems.

    The kind of vegetable you administered then was not the critical factor.

    Mealworms have no absolute requirement for added moisture (or nutrition) from vegetables/tubers/fruit if they are reared on grain.

    The metabolism of carbohydrates itself spins of internal water molecules & they somewhat surprisingly are able to absorb water at their rectum.

    I find yellow mealworm larvae uninterested in supplemental vegetable moisture until they are larger (late instar).

    I like wheat bran as their substrate & it has niacin (a B vitamin), which laboratory bug diets include. It gets favorably involved with biochemical reactions to reduce oxidative “stress” & make available the dietary carbohydrates’ energy.

    I don’t recommend re-using gloves for different bug colonies. Unless you developed a mealworm allergy washed hands should be better than gloves; a face mask against kicked up “dust/frass” is more indicated.

  • Battery going ... I give the adult beetles radish & larvae carrots when old enough.

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