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Recent Nutritional Studies of Feeder Insects discussed by Ayana Evans with Mark Finke, PhD & Nutritionist -- 8 December 2023
Ayana Evans' questions followed by
Mark Finke, PhD & nutritionist's replies
I had an email conversation with Mark Finke, a PhD nutritionist who has published some studies on the nutritional value of feeder insects, and got his permission to share my questions and his answers. Note that there’s a difference between gut loading and feeding feeders a maintenance diet.
Question 1: Do you think a varied diet is better than a diet consisting of a single feeder that has the most studies on gut loading and nutritional content like crickets?
Until nutrient requirements are better known a varied diet is always better than 1 or 2 species IMHO. Deficiencies in 1 feeder may be compensated for by overages in another. That said the base should be a hemimetabolous insect (like crickets or roaches) or holometabolous insect adults (like mealworm BEETLES) rather than larvae because larvae are so high in fat. Again it doesn’t make them bad but probably somewhere in the 10-30% larvae is where you want to be although you might go higher for skinny recovering insectivores and lower for those that are fat and need to lose weight.
Question 2: I have heard that dubia roaches don’t have linoleic and linolenic acid, can this be gut loaded into them?
I don’t know if it’s true for Dubia but it is true that some roach species cannot SYNTHESIZE linoleic acid but if you put it in their diet they will readily accumulate it. Same is true for linolenic acid and EPA and DHA. The fatty acid content of insects is easily manipulated by their diet. There are dozens of studies showing that across a range of insect species. You can also gut-load them but a better course of action is to feed them a diet rich in linoleic and linolenic acid with some EPA & DHA. I can help with good sources of those nutrient if you want.
Question 3: How important is the moisture content of feeder insects for the health of reptiles? Should I prefer crickets over dubia roaches because of their slightly higher moisture content?
It’s important but insectivores can “make water” – we call it metabolic water from other nutrients. The differences between roaches and crickets is likely immaterial and any reported differences is likely more a function of life stage than anything else. I don’t have data on roaches but they likely would be just like crickets (see below) in that the younger the cricket the more water and less fat it has (they are always inversely related) and as they grow older they accumulate more fat (for reproduction) and contain less water. Most animals will appropriately adjust their free water intake if given the opportunity so I would guess most insectivores would adjust appropriately if you provide free water. The only animal that I know that doesn’t do a great job of adjusting their free water intake are domestic cats. They take in less water when fed dry diets which makes SOME cats prone to urinary tract diseases. The table below shows some unpublished data of mine looking at the moisture and fat content of crickets by size (each point is and average of 3 analysis taken over the course of about 6 months from three different lots of crickets.
Cricket Moisture (%) Fat (%)
1/8 78.2 2.9
¼ 76.3 4.1
½ 73.9 5.3
¾ 73.9 5.5
Prewings 71.9 6.4
Audit females 69.3 4.9
Adult males 72.7 3.3
Question 4: Can I increase the vitamins in feeders on a homemade diet mixed with a reptile multi vitamin supplement?
If you give insects vitamin E in their diet they will accumulate it and they will also accumulate beta-carotene but not “preformed vitamin A/retinol”. Almost no risk of overages for those two. I have tried to increase the vitamin B (thiamine, riboflavin, niacin and others) content of insects via diet and have not had much success. Fortunately most insects appear to be good source of most B-vitamins although crickets and likely some others are not terribly high in thiamine. You obviously can increase that via gut loading but to actually increase the vitamin content of the insect itself the only data I’m aware of suggests that only works for vitamin E and beta-carotene. You can increase the vitamin D content of most insects by irradiating them under UV light.
Question 5: When you say that feeders won’t accumulate pre formed vitamin A do you mean that they won’t accumulate pre formed from eating beta carotene, or they just won’t accumulate it at all even if they consume pre formed?
If you feed insects retinol (preformed vitamin A) it will simply pass through them. They will not retain it. If you feed them beta-carotene (which is 2 molecules of retinol attached “tail to tail”), they will accumulate it readily. [Then when the insectivore eats the insects they can cleave the beta-carotene into retinol.]
Pending on 4 March 2024: Portland, Oregon's Lisa Harrenstien, DVM, Dipl. ACZM, (& my exotics vet), disagrees with the last sentence of Mark Finke, PhD & Nutritionist's answer to question 5. Dr. Harrenstien replies instead that "An insectivore will only be able to cleave beta-carotene into retinol if they naturally in the wild eat plants, which leopard geckos don't."
Question 6: I have been told that insects may not be able to absorb the vitamins in animal feed because those vitamins are coated in a substance that protects it from cooking processes, is this true?
For vitamin A & D (and beta-carotene) there are forms that protect the vitamins for being degraded during processing. It’s likely not that they can’t absorb it but rather those are relatively (from the perspective of an 50-200 mg insect) large hard particles that are unlikely to be ingested by most insects. If I gave you a bowl of cereal and put three golf balls in there you’d likely just eat around them. Same thing here. Note the b-vitamins are pretty stable during processing so they should be utilized by insects just fine.
Question 7: I am currently breeding mealworms on chicken layer crumbles but I am not sure what would be a good amount of vitamins to raise them on before I use a gut loading diet to correct the calcium-to-phosphorus ratio. The chicken layer crumbles have 3,000 IU/LB (approx. 6,600 IU/kg) of vitamin A, 800 IU/LB (approx. 1,760 IU/kg) of vitamin D3, and 12 IU/LB (approx. 26 IU/kg) of vitamin E. Is this enough to accumulate a good amount of vitamins in the mealworms as they grow or do I need more?
Your mealworms won’t absorb any vitamin A or D from that diet. It passes through although if you used it for gut loading it would work but frankly those levels are pretty low. The vitamin E is absorbed but that’s about 25 IU/kg so I’d want to be in the 100 to 200 IU/kg range to improve the nutrient profile of the mealworms.
Question 8: Do you recommend a certain amount of beta carotene to raise feeder insects on?
Don’t know exactly but the more the better. You can’t overdose beta-carotene either in the insect or the insectivore. Carrots as a water source would likely work well.
Question 9: I would like to know some good sources of DHA, EPA, linoleic, and linolenic acids for roaches as you mentioned before.
If your diet is grain based there will be PLENTY of linoleic acid for sure. The best source of linolenic would be flaxseed but beware of flaxseed oil as it’s pretty unstable once it’s extracted from the seed. Chia seeds would work as well but flax is likely a better option assuming they will eat it. You likely don’t need to give them EPA or DHA consistently but given its role in neural development I’d try and get it in nesting insectivores hoping it carry’s into the egg or when the young have hatch. Fish oil varies widely in quality and some of the low grade stuff likely smells/tastes fishy which might affect palatability. So if you can find more refined fish oil then it should be more likely to be accepted by the insect and then accumulated in their fat.
(Note: Algae oil is also a good source of EPA and DHA)
If you have any other questions then you can contact Mark Finke here.
markfinke@desertinet.com
