Thermal Preference and Tolerance of the Black Soldier Fly, Hermetia illucens L. (Diptera: Stratiomyidae) Based on Development Stage, Age, Size, Sex, and Nutrition

Abstract

Thermal tolerance and preference are traits commonly used for mass-producing farmed animals as such traits impact their optimal production. In this study, impacts of stage, age, size, sex, and nutrition (i.e., a low protein (7% dry weight (dw)) high carbohydrate (35% dw) diet (i.e., P7C35), a high protein (35% dw) low carbohydrate (7% dw) diet (i.e., P35C7), and the Gainesville diet as a control (~15% protein and ~ 36% carbohydrate)) of black soldier fly, Hermetia illucens (L.) (Diptera: Stratiomyidae) on their thermal tolerance and thermal preference were examined. Results indicate, 1) for larvae and prepupae, median heat knockdown temperature decreased (e.g., by ~2℃) ontogenically within large size group, while small size resulted in less (e.g., by ~1℃) phenotypic variation. Mean cold knockdown temperature increased (e.g., by ~5℃) from large, young larvae to large, old larvae, while small size young larvae had significantly lower (e.g., by ~5℃) cold knock down temperature. Median thermal preference decreased (e.g., by ~10℃) ontogenically with old prepupae as exceptions. 2) For adults, the individual heat knockdown temperature ranged from 45.0-51.0℃ with larger or older adults having a ~1℃greater than smaller and younger adults on median. However, no differences were found between sex. The individual cold knockdown temperature ranged from 8.0-13.0℃ with ~1℃ greater on median in larger or older females. 3) For nutrition, compared to those developed on the control diet, shifts in diet composition (i.e., synthetic diets) resulted in greater (i.e., at least 0.7, 0.4, and 0.2℃ on average for larvae, prepupae, and adult respectively) heat knockdown temperatures except for those adults fed the P7C35 as larvae. Stage (i.e., differed for 8.7 min on average) impacted black soldier fly chill coma recovery times more than diet. Synthetic diets resulted in lower (i.e., at least 7.3℃ on average) larval thermal preferences but greater (i.e., at least 1℃ on average) adult thermal preferences. These data provide references for black soldier fly mass rearing. However, results are likely population specific, and caution should be applied by industry attempting to calibrate their temperature systems for their farmed population.