Date Published: April 30, 2019
Publisher: Public Library of Science
Author(s): Bertrand Hoc, Grégoire Noël, Joachim Carpentier, Frédéric Francis, Rudy Caparros Megido, Patrizia Falabella.
The black soldier fly (BSF), Hermetia illucens (L., 1758) (Diptera: Stratiomyidae), is an endemic fly species from the tropical, subtropical and warm temperate zones of America. This saprophagous species relies on its environment where it finds the decomposing matter for the larvae to grow. The polyphagous diet and the macronutrient quality (mainly lipids and proteins) of these larvae make them excellent candidates for various applications such as waste and organic material management, incorporation in animal feed or alternative energy source. Although rearing development in temperate regions requires artificial processes to continuously produce high quality eggs and larvae, few studies have been conducted on the mating and oviposition processes governing H. illucens reproduction. Research conducted in semi-artificial rearing conditions showed that the number of mating varied according to the season. It has been speculated that this behavior could be due to differences in the intensity of sunlight caused by the change of seasons. This study aims at evaluating the influence of sex-ratio, density and nycthemeral cycle on H. illucens reproduction. In order to tackle this issue, an artificial set up for oviposition to collect eggs has been developed. This egg collection system aims at centralize oviposition and simplify eggs collection. Two populations with opposite sex-ratio (male-dominant and female-dominant) were selected. Their respective eggs productions have been evaluated for five breeding densities. Eggs weights varied significantly among the densities for each opposite sex-ratio population and female dominant population produced most eggs weight from 6500 individuals /m3. Finally, four nycthemeral cycles (2, 6, 12 and 18h of daily light) were simulated to evaluate the impact of light duration on reproduction. Early oviposition pic associated with a decrease of the oviposition period are shown when H. illucens are exposed to increasing light duration. These experiments enable improvement of the understanding on artificial reproduction of H. illucens.
The black soldier fly (BSF), Hermetia illucens (L., 1758) is a Diptera of the Stratiomyidae family found throughout the world in tropical and warm temperate regions . This polyphagous species represents a high potential agent for waste management . Larvae are able to consume a wide range of substrates such as agricultural byproducts and animal or plant origin organic waste . This consumption is associated with a strong reduction in organic matter volumes [3, 4], opening the possibility to innovative waste treatment technology through the bioconversion by insects . In addition, the larvae represent a biomass rich in proteins and lipids that can be used as feed for livestock such as fish, poultry and pig  or incorporated into biodiesel production . Nevertheless, studies are still needed on the biology of the species in order to evaluate their rearing potential and to develop rearing and reproduction methods [1,5,8]. One of the key steps to mass rear this species is to ensure efficient production of eggs in quantity and quality in order to recover large volumes of organic matter, ensure consistent larval production and maintain progenitors .
Reproduction is a key phase to efficient rearing development of H. illucens. This life cycle step is currently partially studied and a series of failures in H. illucens reproduction (e.g. lack of mating and/or low fertility) have been reported in low volume cages exposed to sunlight , lit with fluorescent tube  or rare-earth lamp . Moreover, the absence of standardized methods further limits the success of reproduction in an artificial environment. This study focused on three parameters conditioning the reproduction: (1) the evolution of sex-ratio on larger colonies, (2) the influence of the density and sex-ratio on the reproduction and finally (3) the impact of the nycthemeral cycle on the reproduction.