The black soldier fly (Hermetia illucens Linnaeus 1758) is a fly (Diptera) of the Stratiomyidae family. The adult fly is black, wasp-like and 15-20 mm long (Hardouin et al., 2003). The larvae can reach 27 mm in length, 6 mm in width and weigh up to 220 mg in their last larval stage. They are a dull, whitish color (Diclaro et al., 2009). The larvae can feed quickly, from 25 to 500 mg of fresh matter per larva per day, and with minimal disturbance on a wide range of decaying organic materials, such as rotting fruits and vegetables, coffee bean pulp, distillers' grains, fish offal, corpses (they are used for forensic purposes), and particularly animal manure and human excreta (van Huis et al., 2013; Diener et al., 2011; Hardouin et al., 2003). In ideal conditions, larvae become mature in 2 months, but the larval stage can last up to 4 months when not enough feed is available. At the end of the larval stage (prepupa), the larva empties its digestive tract and stops feeding and moving (Hardouin et al., 2003). The prepupae then migrate in search of a dry and protected pupation site (Diener et al., 2011). The duration of the pupal stage is about 14 days but can be extremely variable and last up to 5 months (Hardouin et al., 2003). The females mate two days after emerging and oviposit into dry cracks and crevices adjacent to a feed source (Diener et al., 2011). The adults do not feed and rely on the fats stored from the larval stage (Diclaro et al., 2009).
Rearing Hermetia illucens has been proposed since the 1990s as an efficient way to dispose of organic wastes, by converting them into a protein-rich and fat-rich biomass suitable for various purposes, including animal feeding for all livestock species, biodiesel and chitin production (van Huis et al., 2013; Diener et al., 2011). The black soldier fly is an extremely resistant species capable of dealing with demanding environmental conditions, such as drought, feed shortage or oxygen deficiency (Diener et al., 2011). One major advantage of Hermetia illucens over other insect species used for biomass production is that the adult does not feed and, therefore, does not require particular care. It is also not a potential carrier of disease. The larvae are sold for pets and fish bait, and they can be easily dried for longer storage (Leclercq, 1997; Veldkamp et al., 2012). A disadvantage of the black soldier fly for biodegradation is that it requires a warm environment, which may be difficult or energy-consuming to sustain in temperate climates. Also, the duration of the life cycle ranges between several weeks to several months, depending on ambient temperature, and the quality and quantity of the diet (Veldkamp et al., 2012). In aquaculture, using feeds based on black soldier fly larvae open additional marketing opportunities for farmers as some customers are opposed to the use of fishmeal in aquaculture feeds (Tiu, 2012).
Several methods for rearing black soldier flies on substrates such as pig manure (Newton et al., 2005), poultry manure (Sheppard et al., 1994), and food wastes (Barry, 2004) have been designed. Rearing facilities use the migrating behaviour of the prepupae for self-collection: larvae climb up a ramp out of a rimmed container to eventually end in a collecting vessel attached to the end of the ramp (Diener et al., 2011). Optimum conditions include a narrow range of temperature and humidity, as well as a range of suitable levels of texture, viscosity, and moisture content of the diet. Temperature should be maintained between 29 and 31ºC, though wider ranges may be feasible. Relative humidity should fall between 50 and 70%. Higher relative humidity makes the diet too wet, and more generally the diet should have enough structure, otherwise the larvae may have a difficult time crawling on it, consuming it and getting an adequate oxygen supply (Barry, 2004).
It is also necessary to maintain a year-round breeding adult colony in a greenhouse with access to full natural light. The greenhouse must be a minimum of 66 m3 to allow for the aerial mating process (Barry, 2004). Ranges of optimal temperatures, for mating and ovipositing, of 24-40°C or 27.5-37.5°C have been reported (Sheppard et al., 2002). Wide ranges of relative humidity are tolerated: e.g. 30-90% (Sheppard et al., 2002), or 50-90% (Barry, 2004). The greenhouse will need a container with a very attractive, moist medium to attract egg-laying female adults (Barry, 2004).