Feed Conversion, Survival and Development, and Composition of Four Insect Species on Diets Composed of Food By-Products

Conventional animal production drives a large share of human-caused greenhouse gas emissions, consumes vast amounts of arable land, and much of that burden comes down to one thing: feed. How efficiently an animal converts feed into body mass is the central lever for reducing that impact. Insects have long been proposed as more efficient converters than chickens, pigs, or cattle — partly because they are poikilothermic, meaning they do not burn calories keeping themselves warm. But efficiency isn't a fixed property of a species; it depends on what you feed them. Oonincx, van Broekhoven, van Huis, and van Loon set out to test exactly that. They took four insect species: the Argentinean cockroach, the black soldier fly, the yellow mealworm, and the house cricket, and fed each of them four diets made entirely from food manufacturing by-products. The by-products included beet molasses, potato steam peelings, spent grains, beer yeast, bread remains, and cookie remains. These ingredients were freeze-dried and blended into four distinct diets that crossed high and low protein with high and low fat. Using by-products was itself part of the sustainability argument — under economic allocation, by-products carry a lower environmental cost than purpose-grown feed. The experiment was tightly controlled. Newly hatched larvae or nymphs were assigned to treatments within 24 hours of birth and reared at 28 degrees Celsius, seventy percent relative humidity, and a twelve-hour light cycle. The team measured three key metrics. Feed conversion ratio, or FCR, is the kilograms of feed required to produce one kilogram of weight gain — lower is better. Efficiency of conversion of ingested food, or ECI, is the percentage of eaten dry matter that ends up as body mass. Nitrogen conversion efficiency, or N-ECI, tracks how much of the dietary nitrogen ends up in insect tissue. Together, these three numbers indicate how well a species is using what it eats. The results split cleanly along species lines. Argentinean cockroaches and black soldier fly larvae consistently outperformed yellow mealworms and house crickets. Cockroach FCRs ranged from 1.5 to 2.7 across diets; black soldier flies ran from 1.4 to 2.6. House crickets reached as high as 6.1 on the least suitable diet. For context, poultry FCR corrected to edible product is around 2.3, pork is 4.0, and cereal-fed beef is 8.8. So, cockroaches and soldier flies were matching or beating poultry on some diets. Mealworms and crickets could reach poultry-level efficiency too — but only on specific diets and only after correcting for edible portion, which the authors emphasize as a crucial adjustment. The nitrogen story is where insects most clearly separate themselves from conventional livestock. Cockroach N-ECI peaked at eighty-seven percent on the low-protein, high-fat diet. Black soldier flies ran between forty-three and fifty-five percent. Compare that to conventional animals: cereal beef converts only twelve percent of dietary nitrogen to edible protein, pork twenty-three percent, and chicken thirty-three percent. Even the least efficient insect on the worst diet beats beef. That is a striking gap, and it holds across all four species. ECI, the dry-matter conversion efficiency, follows the same pattern. Argentinean cockroaches reached up to thirty percent on the low-protein, high-fat diet. Black soldier fly ECIs sat between seventeen and twenty-four percent. Yellow mealworms without any carrot supplementation had ECIs between seven and twelve percent. House crickets were lowest, between five and twelve percent. The rank order is consistent — cockroaches and soldier flies lead, while mealworms and crickets trail — but all four can be competitive with conventional livestock given the right diet. Diet didn't just affect efficiency; it reshaped survival and development time, sometimes dramatically. Argentinean cockroaches took between two hundred and two hundred ninety-four days to develop depending on diet — roughly seven months versus ten months. House crickets ranged from forty-eight days on the control diet to one hundred sixty-seven days on the low-protein, high-fat diet. Yellow mealworms without supplementation ranged from one hundred sixteen to two hundred twenty-seven days. Black soldier flies were the outlier: they completed development in as few as twenty-one days on the best diet and never more than thirty-seven days. Diet didn't affect their survival either — it stayed between seventy-two and eighty-six percent regardless of what they ate. For the other three species, survival and development time were tightly correlated. Faster development predicted higher survival, with Pearson correlations of negative zero point seventy-one for cockroaches, negative zero point fifty-two for mealworms, and negative zero point seventy-two for crickets. The production implication is direct: longer development means longer production cycles, more feed consumed, and more infrastructure time used. The carrot finding for yellow mealworms is specific enough to deserve its own moment. When researchers added carrot — zero point thirty grams of fresh carrot three times a week — to mealworm treatments, development time dropped sharply and survival stabilized at around eighty percent across most diet combinations. Development fell to as little as eighty-three days on the high-protein, low-fat diet with carrot, compared to over two hundred days on some diets without it. The authors suggest the carrot functioned primarily as a water source, though they note that other nutrients such as beta-carotene may have contributed. Either way, one small addition produced a large practical benefit. Then there's what's inside the insects. Chemical composition varied across species and diets, but the degree of variation differed sharply. Argentinean cockroaches were highly plastic: crude protein ranged from thirty-seven point five percent of dry matter on the low-protein, high-fat diet to seventy-two point five percent on the high-protein, low-fat diet. Black soldier flies were far more stable — crude protein held between thirty-eight point three and forty-six point three percent regardless of diet, and phosphorus, though higher overall at six point four to nine point seven percent dry matter, was less diet-responsive. Fatty acid composition tells an even clearer story. The dominant fatty acid in black soldier flies was lauric acid — a medium-chain saturated fat — which made up between a third and a half of all fatty acids in soldier fly tissue. That is a composition the diet cannot easily override. When dietary fat was low, soldier flies converted other fatty acids into lauric acid; when fat was high, they retained more dietary fatty acids, but the profile didn't mirror the diet. The paper concludes there are limited possibilities to tailor soldier fly fatty acid composition through diet. Cockroaches, by contrast, selectively accumulated oleic acid — especially on the high-protein, low-fat diet — and their linoleic acid content swung from one point seven to nineteen point five percent of total fatty acids depending on what they ate. The nutritional n-six to n-three fatty acid ratio — the ratio of omega-six to omega-three fats, where lower is generally considered better for human health — varied widely. Experimental diets had ratios between four point nine and thirteen point five. Insect tissues ranged from five point eight to over one hundred. No insect species fell below the commonly cited optimal ratio of five, and yellow mealworms consistently had ratios above twenty on all diets. So while insects are nutritionally rich, the specifics of their fatty acid profiles depend on species and are not uniformly adjustable through diet. The overall picture that emerges from Oonincx and colleagues is not that insects are a simple drop-in replacement for conventional livestock. It's more precise than that. Argentinean cockroaches and black soldier flies convert feed — even low-value food by-products — more efficiently than mealworms and crickets, and more efficiently than most conventional production animals. Mealworms and crickets can reach poultry-level efficiency on suitable diets. All four species outperform conventional livestock on nitrogen efficiency. But diet composition shapes survival, development time, and body chemistry in ways that matter enormously for practical production. The dual-use angle matters here too. Some of these species are already being produced for human food — house crickets have been raised for consumption in Thailand and Laos for years. Others, like black soldier flies, are used as fish feed. The research doesn't point to a single winner; it points to a framework. Match the species to the diet, optimize the combination for the target nutrient profile, and the environmental case for insect protein becomes concrete rather than theoretical. That's what this study makes possible. This lecture was created by ennepō. Go to https://ennepo.ai to Discover, Create and Follow the latest research in your field. Read when you can. Listen when you want to.