Organic Value Recovery Solutions LLC © Organic Value Recovery Solutions 2010 © Organic Value Recovery Solutions 2010 Insect Digestion of Manure By D. Craig Sheppard and G. Larry Newton An Excerpt from Manure Management Strategies/Technologies White Paper Submitted to the National Center for Manure and Animal Waste Management By Jeffery Lorimor, Iowa State University Ron Sheffield, North Carolina State University Ted Funk, University of Illinois Charles Fulhage, University of Missouri Ruihong Zhang, UC Davis D. Craig Sheppard, University of Georgia G. Larry Newton, University of Georgia August 2001   Insect Digestion of Manure Insects, especially various fly larvae (maggots) and beetles readily feed on fresh manure, converting residual protein and other nutrients into biomass, which is a high quality animal feedstuff.  Considerable research has been conducted to understand and exploit this activity for manure management.  Scientists in China, USSR, USA, Mexico, Eastern Europe, Israel, Australia and Central and South America have studied manure digestion with insects to produce high quality feedstuff.  Lately, the emphasis has shifted from feedstuff production to potentially using insects to solve the problems associated with the large amounts of manure produced at CAFO’s.  While incorporating and concentrating nutrients from manure into more valuable biomass (animal feedstuff), insect larvae reduce the nutrient concentration and bulk of the manure residue, thus reducing pollution potential 50- 60% or more.  Because of its much higher value ($500/ton), this feedstuff can be economically hauled significant distances to relieve local nutrient overloads.  Also, while occupying the manure the insects aerate and dry it, reducing odors.  Maggots modify the microflora of manure, potentially reducing harmful bacteria. The high-value insect feedstuff, reduction of the manure mass, moisture content, offensive odor and pollution potential are the returns for good management of such a system. All published work known to the authors on insect digestion of manure relates to maggot production.  High reproductive and growth rates make flies (maggots are the larval, growth stage) the best candidates.  Flies that have been used experimentally to process manure  include house flies (Musca domestica), face flies (Musca autumnalis), blow flies (usually Sarcophaga sp.) and the black soldier fly (Hermetia illucens). Except for the black soldier fly (Furman et al. 1959), all of these are considered pests as adults due to their disease vector potential, behavior and preferred habitats.  Most current research is being done with the house fly and black soldier fly, so the following discussion will be primarily limited to these. Papp (1974) reported an 8% conversion of pig manure to house fly larvae (dry matter, d.m. basis).  Chiou and Chen (1982) found that blow flies converted 50 to 60% (depending on feeding rate) of swine fecal mass to larval mass, including recovery of up to 55% of the manure organic carbon as larval carbon.  Black soldier fly larvae converted manure in a 460 hen facility to self-collected prepupal biomass at a 7.8% (d.m. basis) rate (Sheppard et al. 1994), which would represent 58 tons from 100,000 hens in 5 months.  House flies under optimum laboratory conditions converted poultry manure to pupae at a 7.6% rate (Miller et al. 1974).  In a recent study with swine, the authors observed 15% d.m. conversion of manure to black soldier fly prepupae.  Research by Engineering, Separation and Recycling (L.L.C.) of Washington, LA found a 24% d.m. conversion of food waste to soldier fly prepupal biomass.  The mouth parts of soldier fly and blow fly larvae allow them to macerate solids, apparently resulting in utilization of greater proportions of solid resources than is possible with house fly culture.  Manure-fed maggots convert feed to weight gain with at least the efficiency of our most efficient concentrate fed domestic animals.In all successful published trials fresh, aerobic manure was used.  Beard and Sands (1973) and Morgan and Eby (1975) reported that anaerobic manure was lethal or at best “unsuitable” for fly larvae development.  Even aerobic manure a few days old supported significantly less survival and growth of house fly larvae.  This reduced performance may be due to depletion of nutrients by microorganisms or development of conditions directly detrimental to larval development.  Beard and Sands (1973) wrote that established house fly larvae slowed bacterial growth.  Black soldier fly larvae also require fresh manure.  Old or stockpiled manure has supported poor larval growth. Because of the need for very fresh manure, insect digestion is best done as a continuous process directly under the poultry or livestock.  This allows for immediate consumption before any competitive bacterial action and saves expense of handling.  The manure is reduced in-place and less hauling is required.  Serial batches started at short intervals have been successful with house flies (Morgan and Eby 1975, Eby and Denby 1978), but require much more labor and a separate facility.  The black soldier fly is well suited to continuous digestion directly under the animals (Sheppard et al. 1994). Twenty or thirty years ago dense soldier fly populations were common in open-sided poultry and swine housing where they were held on wire or slats.  Here soldier fly larvae were present by the millions in a layer covering the manure bed.  Fresh manure was consumed immediately.  Adults were hard to find since only the ovipositing females returned to the facility.  These situations were common in the southeastern US and west to California (Furman et al. 1959).  These unmanaged populations eliminated house fly breeding and reduced manure residue (Sheppard et al. 1983) but feedstuff harvest was never attempted.  A simple ramp and pipe system has been developed (Sheppard et al. 1994) which directs migrating prepupae to collection containers.  Modern, environmentally controlled animal housing makes the manure inaccessible to soldier fly adults, even though house flies often flourish there.  Recently developed rearing techniques for black soldier flies (Sheppard et al. in manuscript) allow for introduction of immatures to digest manure in these modern facilities. Bacteriological interactions associated with manure digestion by maggots are favorable.  Maggots are competitors with bacteria for nutrients and often reduce bacterial numbers greatly, or eliminated them altogether (Beard and Sands, 1973; Sherman, 2000).  Maggots may consume and digest microorganism, and produce antibacterial and/or fungicidal compounds (Landi, 1960; Hoffmann and Hetru, 1992; Levashina et al., 1995 and Landon et al., 1997).  As maggots reduce pathogens in manure they may make it safer for organic vegetable production.  Foodborne illness associated with fresh produce has doubled in the last 20 years and is associated with the increased use of animal manure as fertilizer.  E. coli: 0157:H7 cases are eight times more likely among people who consume organic foods than those who do not.  A preliminary study with black soldier fly larvae indicated a reduction in E. coli 0157:H7 in an artificial medium innoculated with  larvae.  Numerous studies using dried, rendered and fresh maggots as animal feed have revealed no health problems resulting from this practice.  Bacterial culturing of self-collected soldier fly prepupae from a recent swine trial revealed no pathogens. House flies have been the agent of choice in most studies because of their high reproductive rate, short life cycle (2 weeks at 25C), well understood biology, and the ability to flourish in virtually any animal manure.  El Boushy (1991) reviewed the use of  house flies to convert manure to high quality animal feed.  With any fly species to be used as feed, mature larvae or pupae are the preferable stage for harvest.   Losses of biomass by migrating larvae and in pupal development cause the adult to be about half the weight of the mature larvae (Papp 1974) and the more chitinous exoskeleton of the adult may reduce nutrient availability. Feeding studies with house fly and blow fly based feedstuffs have shown them to be generally equal to soybean meal (and other conventional ingredients) in feed value when fed to chicks, rats, pigs, or trout (Calvert et al, 1969; Dashefsky et al., 1976; Finke et al., 1989; Gawaad and Brune, 1979; Too et al., 1980; Teotia and Miller, 1974; Poluektova et al., 1980; Khan et al., 1999).  Soldier fly prepupae have been fed experimentally to several animals, replacing soybean or fish meal, along with added fat, in formulated diets.  The prepupae used in these trials contained 41-42% crude protein, 31- 35% ether extract, 14-15% ash, 4.8-5.1% calcium, and 0.60-0.63% phosphorus, on a dry basis.  These feeding tests utilized chicks (Hale 1973), pigs (Newton et al., 1977), catfish and tilapia (Bondari and Sheppard, 1981, 1987), or frogs (Newton and Sheppard, unpublished data).  The general conclusion of each of these studies was that soldier fly larvae or larval meal was a suitable replacement for a high proportion of conventional protein and fat sources.  A recent replicated catfish fingerling feeding study demonstrated that BSF prepuape can replace high quality fishmeal with essentially the same growth, in spite of losses apparent with the fresh chopped prepupae.  Fish on both diets tripled weight in 55 d.  The menhaden fishmeal fed as the standard in this study is valued at about $500 per ton on the commodity market (2/02).  Separation of the protein and fat in the larval meal by rendering would have allowed for more precise diet formulation. Experimental rendering of soldier fly prepupae produced a meal with 62% crude protein and an oil which was high in desirable medium chain and monounsaturated fatty acids (Sheppard and Newton, 1999), but house fly pupae are reported to be considerably higher in unsaturated fatty acids (Calvert et al., 1969) than soldier fly larvae.  In addition, it may be possible to extract other potentially valuable products, such as chitosan or antimicrobial peptides, from fly larvae or pupae. Insect digestion of manure as a primary treatment is promising.  This process reduces manure mass, nutrient content, moisture and odor, while producing high quality feed.  Most studies have been conducted with the house fly because it is easily reared and well known.  High energy and equipment costs probably explain why house fly systems have not been adopted.  Better understanding of the biology and culture techniques for the black soldier fly are supporting development of a very low cost system to exploit the advantage of insect digestion of manure.  Factors relating to the use of these two insects are given in Table 1.  There is still considerable interest in using house flies for manure digestion, notably in Israel and Chile.  A better understanding of how to utilize the black soldier fly is generating interest in the US, Vietnam, Israel and Columbia.  Engineering, Separation and Recycling (L.L.C.) from Washington, Louisiana has developed and patented innovative manure handling equipment to compliment soldier fly manure digestion by removing the oldest manure from the bottom of the basin.  This facilitates the continuous process. Current research needs include developing practical commercial scale systems, determining optimum utilization of the high value insect based feedstuffs, determining bacterial interactions, including safety of feedstuffs and developing more efficient culture techniques for the black soldier fly.  Nutrient depletion of manure residue following maggot digestion has been variable.  Studies on maggot culture and environmental conditions are needed to maximize nutrient reduction, especially phosphorous. Literature Cited Beard, R.L. and D.S. Sands.  1973.  Factors affecting degradation of poultry manure by flies Environ. Entomol. 2: 801-806. Bondari, K. and D.C. Sheppard.  1981.  Soldier fly larvae as feed in commercial fish production.  Aquaculture 24: 103. Bondari, K. and D.C. 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