Growth and Fatty Acid Composition of Black Soldier Fly Hermetia illucens (Diptera: Stratiomyidae) Larvae Are Influenced by Dietary Fat Sources and Levels

Simple Summary The black soldier fly Hermetia illucens is a potentially promising feed or food source due to its valuable nutritional composition. However, its fat content and fatty acid composition significantly vary with the rearing substrates, making it a flexible resource in fat quantity and quality. Recent research has attempted to manipulate the fat content and fatty acid composition of the insect with modulated feed formulation. Nevertheless, the results of most investigations are not comparable, since the rearing substrates used are various organic wastes with complex substrates. Therefore, it is necessary to perform a quantitative and accurate assessment of dietary fat on larval yield and fatty acid composition. In this study, the influence of two supplemental levels of six dietary fat sources on growth and nutrient composition was evaluated, especially fatty acid composition of black solider fly Hermetia illucens larvae. Additionally, the relationships between dietary fat and larval growth and fatty acid composition were quantitatively determined. Our work deepens the understanding of the fat/fatty acid needs of this insect and therefore enlightens the purposive culture of insects for appropriate fat supply. A 16-day rearing trial was performed to investigate the influence of two supplemental levels (5% and 10%) of six dietary fat sources (linseed oil, peanut oil, coconut oil, soybean oil, lard oil and fish oil) on the growth, development and nutrient composition of black solider fly larvae. Our results demonstrated that the pre-pupa rate of larvae was linearly influenced by dietary C18:0, C18:3n-3 and C18:2n-6 content (pre-pupa rate = 0.927 x C18:0 content + 0.301 x C18:3n-3 content-0.258 x C18:2n-6 content p < 0.001)), while final body weight was linearly influenced by that of C16:0 (final body weight = 0.758 x C16:0 content, p = 0.004). Larval nutrient composition was significantly affected by dietary fat sources and levels, with crude protein, fat and ash content of larvae varying between 52.0 and 57.5, 15.0 and 23.8, and 5.6 and 7.2% dry matter. A higher level of C12:0 (17.4-28.5%), C14:0 (3.9-8.0%) and C16:1n-9 (1.3-4.3%) was determined in larvae fed the diets containing little of them. In comparison, C16:0, C18:1n-9, C18:2n-6 and C18:3n-3 proportions in larvae were linearly related with those in diets, with the slope of the linear equations varying from 0.39 to 0.60. It can be concluded that sufficient C16:0, C18:0 and C18:3n-3 supply is beneficial for larvae growth. Larvae could produce and retain C12:0, C14:0, and C16:1n-9 in vivo, but C16:0, C18:1n-9, C18:2n-6 and C18:3n-3 could only be partly incorporated from diets and the process may be enhanced by a higher amount of dietary fat. Based on the above observation, an accurately calculated amount of black soldier fly larvae could be formulated into aquafeed as the main source of saturated fatty acids and partial source of mono-unsaturated and poly-unsaturated fatty acids to save fish oil.