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How To Raise Larvae On Food Scraps To Feed Livestock

Black soldier fly larvae devour food waste and other organic matter and are made of 60% protein. But they’re increasingly dying before they reach livestock facilities as animal feed.

Researchers, recognizing the culprit is the collective heat generated when the maggots eat in crowded conditions, have found that delivering the right amount of airflow could help solve the overheating issue. Their findings appear in the journal Frontiers in Physics.

“Black soldier fly larvae are widely used in an emerging food-recycling industry. The idea is to feed the larvae with food waste and then turn them into chicken feed,” explains first author Hungtang Ko, a PhD student in the George W. Woodruff School of Mechanical Engineering at Georgia Institute of Technology. “These larvae make a great candidate for this process because they eat just about everything.”

Each year humans waste more than one billion tons of food, or a third of all food production, and many countries are running out of options for disposing of this waste.

The larvae thrive in and around compost piles, where their larvae help break down organic material, from rotten produce to animal remains and manure. Black soldier fly larvae commonly grow to about 1,000 times their size, notes David Hu, professor in the School of Mechanical Engineering.

“It’s like going from the size of a person to the size of a big truck,” he says of the larvae’s growth from eggs to adults.

Hu has appeared on “Science Friday” graphically showing the voracious appetite of black soldier fly larvae, which can eat twice their body mass in food per day. But when these maggots feed while tightly packed in container bins, they generate metabolic heat that collectively can turn lethal for them.

AIR FLOW AND ‘ACTIVE MATTER’

Ko and Hu collaborated with Daniel Goldman, professor in the School of Physics, to set up the experiments. Goldman uses fluidized beds—widely used in industrial applications like oil refining―to control properties of granular media in animal and robot locomotion studies. Fluidized beds operate by forcing a vertical flow of fluid through a collection of particulate matter; above a certain flow rate, the grains transition from a solid pile to a fluid-like arrangement, where they collide and jostle.

The researchers placed the larvae in a container subjected to regular air flow at a consistent temperature. They then attached a leaf blower to supply air flow into the chamber, manually ramping up and down the air speed in five-minute trials.

Because of the larvae’s constant activity, the collectives’ behavior under air fluidization differs from what is observed in traditional fluidized beds: larvae were un-jammable when air flow became low. Instead, they behave like a fluid that adapted and adjusted to external forces.

“An interesting aspect of this work is that it probes a regime of ‘active matter,’ which has received less attention from physicists: Instead of 3D swarms composed of widely separated, non-colliding flying birds and insects, our ‘swarm’ exists in another regime, where animals are packed tightly together,” Goldman says.

In a second experiment, the team used X-ray imaging and constant air speed to see how fast larvae eat. Specifically, Ko measured the average velocity and pressure of the larvae, as well as how much food they ate under various airflow speeds.

“As you continue to increase the flow, you’ll reach a point where all the larvae are flying [through the air]. The airflow is too fast, and they won’t eat well,” he says.

Optimal air velocity will ensure the larvae are cooled off properly and can still feed effectively. “Probing optimal flow velocity will be a good next step. Also, from an engineering perspective, we need to consider other ways that we can cool the larvae down, including using heat transfer,” he adds.

The results indicated that as larvae are agitated by rapid flows, the insects are more likely to be suspended in mid-air without contacting the food, suggesting that a moderate flow rate would be optimal for feeding dense groups of larvae.

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