Threshold temperatures and thermal requirements of black soldier fly Hermetia illucens: Implications for mass production

Abstract

Efforts to recycle organic wastes using black soldier fly (BSF) Hermetia illucens into high-nutrient biomass that constitutes a sustainable fat (biodiesel) and high-quality protein ingredient in animal feeds have recently gained momentum worldwide. However, there is little information on the most suitable rearing conditions for growth, development and survivorship of these flies, which is a prerequisite for mass production technologies. We evaluated the physiological requirements for growth and reproduction of H. illucens on two diets [spent grains supplemented with brewers' yeast (D1) and un-supplemented (D2)]. Development rates at nine constant temperatures (10-42°C) were fitted to temperature-dependent linear and non-linear day-degree models. Thereafter, life history table parameters were determined within a range of favourable temperatures. The thermal maximum (TM) estimates for larval, pre-pupal and pupal development using non-linear model ranged between 37.2 ± 0.3 and 44.0 ± 2.3°C. The non-linear and linear day-degree model estimations of lower developmental temperature threshold for larvae were 11.7 ± 0.9 and 12.3 ± 1.4°C for D1, and 10.4 ± 1.7 and 11.7 ± 3.0°C for D2, respectively. The estimated thermal constant of immature life stages development of BSF was higher for the larval stage (250±25 DD for D1 and 333±51 for D2) than the other stages evaluated. Final larval wet weight was higher on D1 compared to D2. The population growth rate was most favourable at 30-degree celsius (°C) with higher intrinsic rate of natural increase (rm = 0.127 for D1 and 0.122 for D2) and shorter doubling time (5.5 days for D1 and 5.7 days for D2) compared to the other temperatures. These results are valuable for the optimization of commercial mass rearing procedures of BSF under various environmental conditions and prediction of population dynamics patterns using computer simulation models.

Fig 1. Illustration of black soldier fly (BSF) Hermetia illucens (Diptera: Stratiomyidae) and high-quality nutrient larval biomass.

Fig 2. Duration of black soldier fly egg eclosion at different temperatures.

Means with different lower-case letters are significantly different (P < 0.05, SNK test).

Fig 3. Development time of different life stages of black soldier fly fed on two diets at constant temperatures.

The middle quartile or the median (line that divides the box into two parts) marks midpoint of the data. Middle box represents 50% of the scores for each treatment and the middle 50% values fall within the inter-quartile range.

Fig 4. Boxplots showing adult black soldier fly female and male longevity at constant temperatures.

Middle quartile (line that divides the box into two parts) shows midpoint of the data. Middle box represents 50% of the scores for each treatment and the middle 50% values fall within the inter-quartile range.

Fig 5. Quadratic model curves describing longevity of adult female and male black soldier flies at constant temperatures.

Quadratic: n(T) = a + bT + cT²; n(T) represents the longevity function at temperature T (°C); a, b and c are empirical parameters of the model.

Fig 6

Mean number of days before oviposition of egg clutch by female black soldier fly (pre-oviposition period) (A) and mean number of eggs laid per female during her lifespan (B) at constant temperatures.

Fig 7. Mean wet weight of black soldier life stages reared on two diets at constant temperatures.

Means within the same treatment with the same lowercase letter are not significantly different. Means within the same temperature regime with the same uppercase letter are not significantly different (P < 0.05, SNK).

Fig 8. Linear model fitted to observed values of development rate of black soldier fly eggs at constant temperatures.

Fig 9. Linear and non-linear models fitted to observed values of the development rate of black soldier fly life stages at constant temperatures.