Effect of temperature on growth, metabolism, and gas exchange in Hermetia illucens larvae reared under commercial and laboratory conditions
The world's socio-economic development is continuously increasing the demand for efficient production of food, feed, and energy from the agricultural sector. In this respect, the emerging production of black soldier fly larvae (BSFL) represents a promising system to upscale low-quality resources to higher-quality resources usable as feed or biodiesel. To optimize BSFL production it is critical to establish methods that are relevant to examine how rearing conditions, including temperature, affect growth, metabolism, and body composition at large scale. In a first set of experiments, we therefore compared how small-scale laboratory respirometry chambers (600 larvae) support gas exchange, growth, and metabolism in black soldier fly larvae (BSFL) with similar measurements obtained from large-scale commercial conditions (>12 million larvae) at ~34-35 °C. Having observed that small- and large-scale systems generated comparable measurements of growth and metabolism, we used our small-scale respirometry system to examine in detail how rearing temperature ranging from 27.0 to 41.9 °C influenced growth, metabolism and body composition in BSFL. Here we found that 7-day growth of BSFL was stable and high at 27, 35, and 39 °C, while a rearing temperature of ~ 42 °C causes a severe, but sublethal, depression of growth and metabolism. Despite the general similarities in total growth over the 7-day period at 27, 35, and 39 °C, we find considerable acceleration of metabolism and development at the two highest rearing temperatures (35 and 39 °C) while lowered rearing temperature (27 °C) reduces CO2 production per kg larvae produced and the lower temperature is also associated with a higher crude protein to crude lipid ratio in larvae after the 7-day growth period. Based on these findings we discuss how continued monitoring of gas exchange in production systems holds a potential to optimize production in the emerging industry of large-scale commercial insect production.
