Impact of age, size, and sex on adult black soldier fly [Hermetia illucens L. (Diptera: Stratiomyidae)] thermal preference

Abstract

Population growth and rapid urbanisation have increased the global demand for animal feed and protein sources. Therefore, traditional animal feed production should be increased through the use of alternative nutrient sources. Insects as feed are beginning to fill this need. One such insect is the black soldier fly, Hermetia illucens L. (Diptera: Stratiomyidae). However, to more effectively mass produce the black soldier fly, a better understanding of its thermal biology is needed. Thus, the aim of this study was to evaluate the impact of age, size, and sex on adult black soldier fly thermal preference. The thermal preference of adult black soldier flies was determined by exposing flies to a thermal gradient with a range of surface temperatures and monitoring their positions over time. An aluminium plate was used to create a linear thermal gradient where surface temperatures ranged from ~15-60 °C. Flies were distinguished by age (1-d-post-emergence vs 7-d-post-emergence), size (large vs small) and sex (male vs female) to assess whether thermal preference differed by specific life-history traits. Thermal preference for 7-d-post-emergence adults was significantly lower (19.2 °C) than 1-d-post-emergence adults (28.7 °C), respectively. Similarly, small adults selected significantly cooler (21.1 °C) temperatures than large adults (26.9 °C). No significant differences in thermal preferences were found between sex, regardless of age or size. In fact, males and females had similar thermal preference of 23.8 and 24.2 °C, respectively. This study reveals that multiple life-history traits of adult black soldier fly affect their thermal preference, and thus should be taken into consideration by mass rearing facilities to optimize production.

Welfare considerations for farming black soldier flies, Hermetia illucens (Diptera: Stratiomyidae): a model for the insects as food and feed industry

“…Studies of critical thermal maxima suggest that 44-46 °C is lethal for adults (Laursen et al, 2021). Age and size (but not sex) determined preferred temperature for adults: young adults (1 day after eclosion) preferred warmer temperatures (28.7 °C) than 7-day-old adults (19.2 °C), while smaller adults preferred cooler temperatures than larger adults (Addeo et al, 2021). Notably, adults were not fed in Addeo et al (2021); thus, negative correlations between age and preferred temperature may be related to reducing metabolic rate under starvation conditions, and this result should be re-examined with fed adults.…”

“…Adult size is closely linked to larval feeding (e.g. Addeo et al, 2021). Adult male and female flies look similar, though males are often smaller in body size (Jones and Tomberlin, 2019).…”

No neonates without adults

“…[46] How mate choice emerges at the population level has not been explicitly explored, but it seems reasonable that bottom-up processes such as these are what lead to the formation of mating aggregations that have been described as "leks" [37] (Figure 3); although we note that the accuracy of this descriptor is not readily apparent for flies in a colony setting, and its use within the Insecta as a whole has been debated. [16] That said, the understanding of mechanisms underlying communication and mate choice within H. illucens are still putative and little is known within the scientific literature about how adult black soldier flies exchange information or navigate within their broader environment or which has been gleaned from relatively few experiments investigating abiotic factors, [40,51,52] varied oviposition substrates, [53,54] and trap materials. [12,28,55,56] Moreover, none is known of the specific mechanisms of how they might achieve long-distance travel to and from wild lekking sites, [37] such as hilltopping, utilizing search images, following conspecifics, or photo-and phonotaxis.…”

“…That said, the understanding of mechanisms underlying communication and mate choice within H . illucens are still putative and little is known within the scientific literature about how adult black soldier flies exchange information or navigate within their broader environment or which has been gleaned from relatively few experiments investigating abiotic factors, [ 40,51,52 ] varied oviposition substrates, [ 53,54 ] and trap materials. [ 12,28,55,56 ] Moreover, none is known of the specific mechanisms of how they might achieve long‐distance travel to and from wild lekking sites, [ 37 ] such as hilltopping, utilizing search images, following conspecifics, or photo‐ and phonotaxis.…”

Particularities of the Hermetia illucens (L.) (Diptera: Stratiomyidae) Ovipositing Behavior: Practical Applications

“…Studies have shown that the reproductive performances of H. illucens are influenced by many factors in the breeding environment, such as temperature [ 55 , 56 ], light [ 57 , 58 , 59 ], humidity [ 60 ], attractive substrate for stimulating ovipositing [ 50 , 61 , 62 ], ovipositing conditions [ 63 , 64 ], etc. The economic efficiency of the rearing and reproduction of this species is therefore greatly influenced by the most detailed knowledge of the particularities of the reproductive process.…”