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Forging a New Food Chain.

Black soldier flies eat manure -- then become livestock feed

Insects are primary animal dung consumers in nature and recycle manure nutrients into food for many wildlife species.

This natural technology, University of Georgia researchers say, could someday benefit humans in managing livestock production and waste.

Insects can extract and concentrate manure nutrients into higher-value products than fertilizer. Through digestion, their larvae reduce manure residue mass and nutrient concentrations. These larvae then become animal feeds rich in high-quality proteins and oils.

Nutrients in manure used as fertilizer can overload available crop land when dispersed from intensive animal production facilities. Often, it is too expensive to haul the material far enough away to apply the nutrients at optimum levels for crop production.

Using insects to produce feedstuff from manure nutrients is an alternative that has been studied in the past. Scientists in China, the United States, Mexico, Eastern Europe and South America have used insect feedstuff to supplement poultry, swine, several fish species, shrimp, turtle and frog diets.

Most of the research has focused on house and blow fly larvae. House flies have been used most often because of their short life cycle, high reproductive rate and ease of culture. However, systems using house flies require moving manure to a facility to contain the insect nuisance and disease vector. Also, mature larvae or pupae must be sifted or otherwise mechanically separated from the manure residue for feed production. Specialized house fly rearing facilities and equipment -- with extra management and energy requirements - increase house fly production costs.

Another option

To make insect feedstuff production more financially palatable, black soldier flies are being enlisted for a manure management system that operates under poultry caged layers or swine housed on slatted floors. For this system, no manure handling is needed. Larvae in dense populations consume manure quickly, which provides odor control and the best nutrient recovery.

About 60 tons of fresh prepupae can be self-harvested from one 100,000-hen caged layer house in five months. This plentiful feedstuff is 42 percent protein, 35 percent fat, high in minerals, and supplies amino and fatty acids. Chitosan -- used in waste and water treatment, cosmetics, toiletries, pharmaceuticals and food processing -- and other valuable insect byproducts could also be extracted from the mix.

The black soldier fly is a large, wasp-like creature of New World origin found globally in tropical and warm regions. Adults live 38 days in the wild, visiting humans just long enough to lay eggs near waste heaps.

Unlike the house fly, adult black soldier flies rarely enter dwellings. Their robust larvae feed on organic matter ranging from manure to formalin-preserved tuna. They have been found in everything from spoiled, wet animal feed and manure to rotting vegetables, cadavers and catsup.

No separate facility or energy input is needed for manure digestion using the black soldier fly because of the migratory habits of this non-pest's large prepupae. The prepupae crawl from the mass of feeding younger larvae to burrow into undisturbed soil where they orient head-up waiting to emerge as adults. Movements of 20 to 40 feet (6 to 12 meters) or more from the manure bed are common. Emergence occurs in 10 to 14 days during warm weather.

The prepupae's migration can be exploited by configuring the manure basin to direct their movement. Manure basin walls built as ramps are about 2 feet (0.6 meter) high. A slotted PVC pipe or gutter at the ramp top directs the prepupae into collection containers. Initial studies involved flushing the larvae from the collection pipe with water. However, this step was determined unnecessary because the larvae travel within the pipe or gutter, when angled at an upward slope.

Buildings using this collection system must be wider than typical facilities so the prepupae traveling ramp under the slatted floor is kept outside the manure "drop zone."

Another option is to install panels over the ramp to deflect falling manure.

Transient prepupae have emptied their gut of manure and their mouthparts are modified into a hook used for migrating and digging. Their empty gut and large store of fat make them ideal for animal feed.

Working with flies

Pilot-scale manure management trials with black soldier flies have depended on egg deposits from wild populations. For a manure management system to work, some accommodation must be made for the wild females to access manure. Many modern environmentally-controlled livestock and poultry facilities are unsuitable for ovipositing females to enter because the insects fly into fans rather than open air intakes.

However, the insect's life cycle can be managed in or near an animal production facility. Recent attempts show that colonizing black soldier flies makes more intensive systems possible. Colony females can be induced to lay eggs on egg traps, which are easily moved to an animal facility to ensure sufficient larvae.

Observations under laboratory and confined colony conditions show that unlike house flies, adult black soldier flies need only water -- no food -- to mature, mate and reproduce. Soldier fly prepupae contain 35 percent fat compared to 9 percent to 16 percent fat in house fly pupae. This large energy store relieves the adult soldier fly of searching for food and the need to provide adult food for a culture.

The flies' fat content differences are based on dry matter. Soldier fly prepupae show consistent values of 44 percent dry matter, which is high for a waste byproduct. House and blow flies are about 30 percent dry matter, giving soldier flies a nutrient density and processing advantage.

Studies on feeding soldier fly prepupae to swine, poultry, fish and frogs have shown no disease problems. Most tests have used fresh or dried prepupae, usually chopped or ground. Prepupae can be rendered using standard commercial processes to produce protein meal and oil, allowing more flexibility in formulating diets that include larval products. Live prepupae combined with a pelleted diet have been fed to bullfrogs.

Another benefit of this system is to control house flies, which cannot reproduce where soldier fly larvae are dense.

Less manure, too

Laying hen manure residue is reduced by at least half by soldier flies when compared to undigested manure. It typically contains a concentration of 24 percent to 30 percent less nitrogen and up to 43 percent less phosphorous compared to same-age undigested manure. When combined with the minimum 50 percent overall reduction, total residual nitrogen becomes about 38 percent of same-age undigested manure. Even in cases where phosphorous concentration is not reduced, phosphorus mass is reduced about 50 percent.

When the factors that cause nutrient reduction variability are identified, they can be managed to better convert manure into insect products. Under the best conditions, manure dry matter conversion into insect dry matter is about 8 percent. Adjusting this percentage to the moisture contents usually found in farm animal diets and body compositions results in a feed conversion efficiency equal to 4 pounds (1.8 kilograms) of feed per pound (0.45 kilogram) of gain. This ratio falls between the amounts commonly reported for broiler chickens or swine, and cattle.

Well-digested hen manure residue is a finely divided substance with reduced odor. It is easily handled using conventional equipment.

Systems for processing swine manure using soldier flies are less developed. Although fresh manure from cattle fed high grain diets is also suitable for soldier fly larvae, feeding facilities are less easily adapted for insect manure processing.

The black soldier fly can benefit the poultry and livestock industries if integrated into manure management systems. Nutrient reductions in manure residues should help improve nutrient management plans and allow animal production to be maintained or increased.

Current trials with pit modifications for swine show promise and if positive results continue, a commercially viable system may soon be developed.

Soldier fly larvae can be used to digest any confined animal or poultry manure. The insects reduce animal waste while providing a healthy livestock food source.

ASAE member G. Larry Newton conducts livestock waste management research at the University of Georgia Coastal Plain Station, Animal and Dairy Science Department, Tifton Campus, P.O. Box 748, Tifton, GA 31793, USA; 229-386-3214, fax 229-386-3219,

D. Craig Sheppard is a associate professor at the University of Georgia Coastal Plain Station, Entomology Department, P.O. Box 748, Tifton, GA 31793, USA; 229-386-3377, fax 229-386-3086,
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Title Annotation:Black soldier flies eating manure
Author:Newton, Larry; Sheppard, D. Craig
Publication:Resource: Engineering & Technology for a Sustainable World
Geographic Code:1USA
Date:Oct 1, 2000
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