Martin H. Villet
Department of Zoology & Entomology, Rhodes University, Grahamstown, 6140 South Africa
The world’s human population is expected to grow to nine billion by 2050, posing two significant challenges: providing enough food for everyone, and disposing of the resulting waste products. What if biotechnology could solve these two problems simultaneously?
Not only are human numbers growing exponentially, but a burgeoning middle class is consuming a diet containing a larger proportion of meat and fish. The traditional protein source for rearing pigs, poultry and fish is fishmeal, but nine billion people will need three times our planets' fish stocks to provide that fishmeal. On the other hand, apart from dumping it, the garbage from nine billion people can be destroyed or recycled. For instance, oil spills and some plastics can be destroyed by getting bacteria to eat them, the familiar technology of biodegradability. Earthworms and insects can also degrade certain organic waste such as leaf litter, manure and agricultural waste. What if biotechnology could recycle these biodegraders into replacements for fishmeal? Scientists in France, Germany, Nigeria and South Africa are keenly interested in developing such alternatives based specifically on flies.
The immature larval or maggot stages of various types of flies feed avidly on waste from livestock farms, abattoirs, vegetable farms and fruit growers, and can be processed into an excellent substitute for agricultural and aquacultural fishmeal. Maggot powder, called ‘magmeal’ in South Africa and Nigeria, is superior to vegetable proteins such as soya and sunflower, both in nutrient value and in efficiency of production, and has the added advantage that it is produced from waste products that must otherwise be dumped at extra cost to the environment and the consumer.
Studies conducted through Idaho State University, the University of Georgia, Humboldt University, Ebonyi State University and Stellenbosch University have shown that magmeal performed better than fishmeal as a protein source for poultry, pork and aquaculture because it is more nutritious. It contains 39–66% crude protein, 12–21% lipid, 6–8% crude fiber, all nine essential amino acids and seven other amino acids, and is also rich in B-complex vitamins, phosphorus and trace elements. The balance of the amino acid profile is good, including sufficient methionine, which can be limiting in other animal and plant protein sources. Its palatability, acceptability and digestibility are good for most types of livestock. Anti-nutritional or toxic factors, which tend to occur in plant-based protein sources, are apparently absent. The nutrient content of maggots’ food has only minimal effects on the nutrient content of the resulting magmeal, providing a more consistent product.
Dietary studies of fish and poultry in which fishmeal was partially or completely replaced with magmeal showed no significant differences in protein utilisation, haematological parameters, stress indicators, feed conversion levels or growth parameters. In poultry, it also resulted in increased egg yield and egg hatchability, and is also associated with decreased gizzard erosion, a dietary deficiency disease affecting younger poultry.
The total production of fishmeal by the world’s 300 fishmeal plants was about 5 million tonnes in 2006-2010, derived from about 15 million tonnes of whole fish and 5 million tonnes of trimmings from fish processed for human consumption. South Africa has an estimated demand of over 2 000 tons per month. Secondary income steams can be generated by charging waste producers for waste removal, and by harvesting the ammonia that maggots excrete.
Excitingly from an environmental and commercial perspective, the cost of harvesting and processing 1 kg of magmeal has been measured as less than 20% of that of 1 kg of fishmeal. The production of magmeal should enjoy greater price stability than fishmeal production because there were fewer price variants associated with the process. Magmeal production facilities sited near to abattoirs or farms would also help to minimise transportation costs.
The production of magmeal commonly involves three species: house flies, black soldier flies and blow flies. House flies and soldier flies breed well in poultry manure, while blow flies excel in abattoir waste. All three flies are naturally associated with humans, and have spread over much of the planet, so that obtaining stocks is not difficult.
All flies’ life cycles go through three stages (egg, larva and pupa) before adulthood. To make magmeal, the maggots are harvested just before the pupal stage, and then dried by heating, milled to a very fine, rich, brown powder and packed. In a lifetime, females of these flies lay 300 and 1,200 eggs, and one kilogram of eggs can turn into over 300kg of protein about 72 hours after they hatch if enough food is available. Five tonnes of maggots, or approximately 200 million maggots, yield about a tonne of magmeal. A facility receiving 6500 litres of blood a day can feed 10 tonnes of maggots and produce two tonnes of magmeal. Because the fly population can increase by two or three orders of magnitude per generation, production is limited mainly by the availability of food.
The crucial issue in commercializing this biotechnology is scaling up the process. In South Africa the concept has been proven on a prototype fly farm that has 22 subunits, each one housing up to 0.75 million flies, and the company has developed designs for industrial plants that will produce the quantities required by the local farming industry - up to 100 tons of live larvae per day, or 840 tons of magmeal per month. The size of a factory depends on the volume of available waste, so that sites where waste production is intensive are ideal.
The design of the factory needs careful attention. It must be sufficiently well sealed to contain the adult flies, and to exclude invasion by unwanted flies of other species. Odours need to be contained too. By rearing the flies at suitable temperatures, their growth rate can be accelerated so that their food has little time to decay, and careful regulation of the ratios of food to maggots can ensure that little food remains to rot and smell. Subdivision of the rearing facility can help to contain infections that maggots are occasionally prone to – yes, even maggots get diseases – and to stagger the production of cohorts of larvae and smooth the production schedule.
A facility for rearing adult broodstock should be kept separate from the area where maggots are reared for harvesting and processing. Apart from protein (to develop eggs) and carbohydrates (for energy), adult flies require a supply of water in which they will not drown.
In the processing plant, adequate heating is needed in the drying process to destroy any pathogenic organisms that were present in the food, and chemical testing should routinely ensure that there is no transfer of veterinary antibiotics or other drugs present in the maggots’ food to the final magmeal product.
Flies are not the only source of protein that could ameliorate the effects of human population growth. Bacteria and algae are being investigated in Asia, and silkworm pupae have been an important dietary component for carp production in Japan and China. These innovations may be only the precursor to another ancient form of food biotechnology that is well known in Asia and Africa. Termed ‘entomophagy’, it is the inclusion of insects directly into our own diets.