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Beetle max population and frass amount

Hi all, i am new here and i am exited about started production of mealworms.

However i have some questions that i hope you can help me with.

1 - Max amount of beetles per sqm In order to calculate or needs in terms of material i would like to know what would be an optimal amount of beetles per sqm for them to feel confortable enough (in human terms) to lay their eggs

2 - What is the amount (in kg) of frass produced by larvas, and beetles per sqm of production

We are planning a start cattle of 15000 heads to beetles, from what i read we should consider a loss ration of up to 10% (usually 3%) - Does any of you have any feedback on this amount of production (giving it might results to approx. 4million larvas)

Thanks in advance




  • edited August 2016

    Hi richardfv, - If you are asking about 4,000,000 yellow Tenebrio molitor larvae at one harvest here are some calculations. Old larvae can have average weight = 139.6-182.7 mg each; thus 4 million weigh 558,400,00 - 730,800,00 mg (= 555,400 gr - 730,800 gr total). Would you confirm that you want to harvest 4,000,000 larvae & give an idea of how often you want to harvest them.

    One issue is they can start toward pupation at 130 - 154.6 gr weight (the nutritional value of pupae is different & not usually desired as a feed ingredient). Data in Table 6 of research cited reveals that once the T. molitor larvae weighs 118-125 mg larval weight it starts to show a negative growth rate. Thus, authors conclude the larvae are best used for food once they are 100 to just under120 mg each larvae . At 120 mg each 4 million larvae weigh 489,000,000 mg or 480,000 gr (=1,058.5 pounds).

    Mealworms were reared on 95% whole wheat flour + 5% brewers yeast, at 25 Celsius, 70% relative humidity with 8 hours light + 16 hours dark; on this specific diet their growth rate was still positive (gaining1.2 mg/d) when harvested at 100-105 mg larval weight each. See Ghaly & Alkoaik's (2009) "The yellow mealworm as a novel source of protein", originally published in American Journal of Agriculural & Biological Science; Vol. 4(4). Free full text link =

  • Frass production might be estimated by using Andrew's " ... 2.5:1 FCR (food conversion ratio) ... for mealworms assuming an imperfect feed, although a carefully balanced diet should yield a better ratio ...." Thus, if harvest yellow Tenebrio molitor larvae at 120 mg then need 300 mg (120 x 2.5) total feed; at this rate excreted feed = 180 mg frass (300-120) per larvae. Meaning 4 million larvae of 120 mg produce 720,000,000 mg frass = 720,000 g (1,587 pounds) frass.

    Elsewhere in Forum I have posted mealworms have a 2.2 food conversion ratio; then the larvae at 120 mg need 264 mg (120 x 2.2) total feed . At this rate excreted feed = 144 mg frass (264-120) per larvae; meaning 4 million larvae of 120 mg produce 576,000,000 mg frass = 576,000 g (1,270 pounds) frass.

  • @gringojay thanks for your reply and thanks a lot for the link.

    Concerning the amount it is correct, however we are planning on harvesting 50% larva and keep the rest for a new round of reproduction, trying to keep a reproduction cattle at about 1.6 million beetle which if correct would result to about a population of 486M larvae (considering loss ratio) from 1 generation (knowingly that beetles could probably have up to 3 rounds of reproduction).

    From my understanding, accordingly to correct environment conditions (27C max and 70% humidity) a maximum cycle from egg to larvae ready to harvest should be maximum 11 weeks (if my research is correct)

    Our aim is to keep a beetle population of 1.6M to be able to produce about 400M larvae per cycle (not taking in consideration more than 1 reproduction round from beetles)

    However i have Absolutely no clues when it come to the best environment setup for beetles nor the amount of frass produced both by larvae and beetles, as we are planning to recycle frass for plants nutrition both indoor and for sale

  • Guess you beat me to the typing as i got your answer after answering you

  • As for total larval area required to rear 1 Kg larvae Andrew (elsewhere in Forum) reported "The bags we're currently producing for the small kits ... are 9" X 23" X ~4"-5" depth". Which means1 Kg. mealworm grow bag needs 1.437 sq.feet (0.1335 sq. meter) of horizontal area to a depth of 4-5 inches (0.1016 - 0.127 mt.) high.

    4 million larvae at 120 mg weighs 480,000g = 480 Kg. Using the above area means a total horizontal area of 689.76 sq feet (1.437 x 480) to a depth of 4-5 inches (= 64 sq. meters horizontal area to a depth of 0.1016-0.127 mt) high can produce 4 million yellow mealworm larvae of 120 mg.

    According to the preceding comment's math: using a feed conversion ratio of 2.5:1 means there will be 7.2 Kg (720,000 gr or 1,587 pounds) frass in the horizontal area of 689.76 sq.ft, or 64 meters, required to rear 4 million mealworm larvae of 120 mg each. Using an alternative feed conversion ratio from a balanced diet of 2.2:1 means there will be 5.76 kg (576,000 gr or 1,270 pounds) frass in the horizontal area of 689.76 sq. ft, or 64 sq meters, required to rear 4 million mealworm larvae of 120 mg each.

  • I think you meant respectively 720Kg (720000gr) and 576Kg(576000gr) 2.5:1 300-120= 180*4000000= 720000000mg=720Kg :)

    Anyways this is very good info, i couldn't find what the amount of wheat needed for beetles as i guess they will require less food.

  • edited August 2016

    Hi richardfv, - At the scale you wish to operate breeding tactics make sense. I see no reason to have so many male yellow Tenebrio molitor beetle, each time they mate they put out 6,200 - 19,400 sperm. A yellow T. molitor male beetle needs ~ 20 minutes to recover before re-mating.

    If the density of males is high each mating involves more sperm since the males pick up clues of male odors. Females allure males with 4-methyl-1-nonanol pheromone & males after mating put out another pheromone to try to cover this up; but the males are wasting resources making this because it is not effective (unless male density is lower than artificial breeding normally sees).

    Lots of males around & a male will spend more time copulating with the same female. Less males around & their courtship, mating & post-copulatory "guarding" (hanging around dismounted at less than 1 cm away from female) are all quicker.

    Also when their aedeagus senses how full their female mate's bursa is of other male sperm-atophores inside.The male's aedeagus can also puncture rival males' sperm-atophores inside the female.

    Sperm is not actually released inside the female until 7- 10 minutes has elapsed. If a female re-mates in under 7 minutes the 1st males sperm is only 40% likely to be what fertilizes an egg.

    Whatever goes on the last male to mate with a female never ends up fertilizing one of her eggs more than half the time; the last male mating only gets an average paternity of 16%. The female does need to mate at least once every 2 days before the number of eggs made starts to decline.

    At high colony density in laboratory conditions the females re-mate quicker, do so with more different mates & there is an increase in the number of eggs produced (in comparison to solitary pairing up). However, even though female T. molitor beetles lay eggs for 1- 2 months the number of eggs laid tapers off at ~ 3 weeks.

    Ovi-position (laying) of eggs is not done in clutches, but usually daily as a burrowed into the substrate grouping of on average 25 (maximum 30) individual eggs. A realistic calculation is the female T. molitor beetle will lay 300-400 fertilized eggs in her breeding life. These eggs are prone to being cannibalized & more males than actually needed, which are driven to produce high sperm counts add to this risk.

    You can assess the sex of T. molitor pupae using the method developed in 1970 by the Univ. Illinois Department of Entomology by Bhattacharya; a low power magnification will make this easier. You can also determine the sex of the adult T. molitor beetle if wish to cull some of those.

    The underside (ventral) of pupae is segmented & sort of plated looking, like a sternum (forming "sternite" sections). The incipient genitalia begin to show as a protrusion where the 7th underside "sternite" section transitions to the 8th underside "sternite" section.

    Male T. molitor pupae protrusion under this 7th ventral segment has short & "blunt" hair like "papillae" emerging. These are visible & clustered toward the mid-line of the underside segment.

    Female T. molitor pupae protrusion under this 7th ventral segment is larger than the male's protrusion. The hair-like "papillae" of the female pupae are not clustered in the same manner of the male pupae, but rather more dispersed along the lateral margins of where they emerge.

    Adult T. molitor beetle sex determination is done at the last underside ("sternite") sections. The male beetle's terminal (last, caudal, 5th "sternite") end appears blunter than the female beetle's; the female "butt" end (caudal end) is pointier than the male (although does not come to a pointed tip).

    Looking at the different membrane segments of their underside (inter-segmental membrane) can also distinguish T. molitor beetle gender. The male has wider inter-segmental membranes than the female in between both the 3rd & 4th "sternites" & also between the 4th & 5th "sternites". In comparison, the female does not have as wide inter-segmental membranes between the 3rd,4th or 5th "sternites".

  • Forgot reference for Bhattacharya, Ameel & Waldbauer's tactic. Title of their short report = "A Method for Sexing Living Pupal and Adult Yellow Mealworms; originally published in 1970 Annals of the Entomological Society of America, 63(6),pg. 1783

  • Egg eating by T. molitor adults can be up to 5%/day according to Gerber & Sabourin who, in a 4 day period under their specific set-up, counted 100 out of 500 eggs were eaten (whether more eaten by one sex or the other was not determined). As per those authors' (1984) "Oviposition site selection in Tenebrio molitor (Coleoptera:Tenebrionidae)", originally published in The Canadian Entomologist.

  • Tanks for The info @gringojay

  • I will keep you updated onde we have started On our side

  • A few more indications for mealworm breeding strategy. The ideal relative humidity & temperature is different for different T. molitor life cycles.

    According to "Studies on the Bionomics and Breeding of Yellow Mealworm" the best relative humidity (RH) ranges are as follows: larvae = 80% RH, pupae = 90% RH (so done by end of 7th day), oviposition = 90% RH & eggs = 75% RH (so hatch by end of 5th day).

    The issue of temperature is more complex; generally we find suggestions for rearing T. molitor from 20 - 30Celsius. According to "Study on the Rearing Larvae of Tenebrio iter Linn'e and the Effects of its Processing and Utilizing" the larvae grow fastest at 20 - 25 Celsius. While on the subject of larvae, according to "Determination of Some Important Technique Parameters in the Coures of Breeding Tenebrio molitor", their optimal rearing density = 0.24-0.47

    Beetle breeding temperatures in experiments are usually not allowed to go over 30 Celsius (ex: 25-29 Celsius range commonly stated). It seems 34 Celsius is a threshold for impacting ovi-position (& development of larvae).

    However, for breeding purposes going over 30 Celsius to the T. molitor upper range for ovi-position may be better if the beetles are given a superior diet. By superior diet I mean something like whole wheat flour instead of bran & adding 1 part of brewers yeast for every 19 parts flour; mix this together & sterilize at 80 Celsius for 24 hours before cooling for hygienic storage & feeding.

    Assure constant moist food for water supply because as temperature goes up mating beetles need more water (female gets some moisture from male sperm-atophore); and mating goes up with temperature. Similarly, as they mate more the beetles also need more nutritious food & the female only gets some extra nutrition from the sperm-atophores. Anticipating both of these factors will help keep beetles from eating the eggs.

    The following paragraphs is what I project for raising the breeding temperature to 32-33 Celsius; it is an extrapolation from a different "flour" beetle. Bear in mind one has to conduct control experiments on only a part of one's T. molitor colony before adapting the concept to a specific breeding temperature. See V.M.Grazer's dissertation (2013)"Evolutionary Consequences of Sexual Selection and Sexual Conflict Due to Environmental Change"; free full link =

    Relative to lower (25-29 Celsius) temperature at a higher temperature the number of progeny/week increases in the initial 21 days of a female's breeding life (see previous comment that this is her peak oviposition phase to begin with) ; but it will decline faster than otherwise (ie: lower temperatures) after ~28 days. The number of live hatchlings will go up within a week after she is mating, decrease by end of 2nd week after she is mating & go up again around the 3rd week after she is mating.

    There will be more progeny from different males & when introduce new male stock this will revitalize future generations (only ~4% of what ejaculates gets into the sperm-atheia of sperm-atophore & # of sperm/egg can drop 50% by his 2nd week of mating). The male is often responsible for lower female longevity; during copulation he can damage her wings & his anatomy during penetration damage her as well. In fact, expect the number of mating females that survive to go down by ~60% after 6 weeks of mating & by ~80% after 7 weeks of mating.

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