Age and calorific restriction impact immature black soldier fly (Diptera: Stratiomyidae) thermal tolerance and preference

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Abstract Thermal tolerance and preference are traits commonly considered when mass-producing farmed animals as temperature impacts production. In this study, the impact of age and calorific restriction of immature black soldier fly, Hermetia illucens (L.) (Diptera: Stratiomyidae) on associated thermal tolerance and preference was examined. Both age (7-d-old for young larvae and 14-d-old for old larvae) and calorific restriction (led to size differentiation, small for calorific restriction and large for non-restriction) within a given stage influenced thermal tolerance (i.e. KR50) and thermal preference. Results indicate the interaction between age and calorific restriction was significant on both larval and prepupal thermal tolerance but not thermal preference. Median heat tolerance KR50 ranged from 46.4 °C (large, old prepupae) to 48.4 °C (large, young larvae). Median cold tolerance KR50 ranged from 21.6 °C (small, young larvae) to 32.1 °C (small, old larvae). Young larvae preferred median temperatures ∼3.0 °C greater than old larvae. Large larvae preferred median temperatures ∼2.0 °C lower than small larvae. Results from this study indicate ontogeny (i.e. stage of development) and calorific restriction have significant impacts on black soldier fly thermal tolerance and preference. Precise regulation of temperature in an industrial setting is necessary for optimal batch production of the black soldier fly (e.g. survival) and for colony maintenance (e.g. prepupae producing adults and potentially eggs). The same can be said with regards to maintaining consistent age and calorific restriction of immatures produced within each batch as variation in such traits impacts thermal tolerance and preference (e.g. survival to harvest for producing protein or adults for colony) as well. The methods and temperatures used in this study could serve as a foundation for developing standard operating procedures for regulating temperatures experienced by black soldier fly larvae industrially produced.