Temperature-modified density effects in the black soldier fly: low larval density leads to large size, short development time and high fat content

Abstract

The effects of biotic and abiotic factors on insect life histories have been extensively studied. However, the impact of some crucial aspects, such as larval density (crowding) and the effects of environmental interactions, have often been overlooked. This study aims to determine the effects of larval density and temperature on life-history traits in the black soldier fly (BSF). Our results showed an increase in prepupal mass, pupal mass, prepupal-to-pupal mass loss, survival, prepupal fat content, adult mass, adult longevity and a reduction in larval and pupal development time at low densities. Larval density was maintained throughout the entire larval period and larval survival was determined at the 4th instar and at prepupation. Larvae were reared at three different larval densities (1, 5 and 10 larvae/cm2), at three temperature treatments (23, 27 and 30 °C) and food was provided ad libitum. High densities, on the contrary, resulted in an increase in development time, mortality and a decrease in prepupal mass loss. Temperature significantly affected all studied traits except survival, prepupal fat content and adult longevity, and notably modified the larval density effects on prepupal mass, pupal mass, adult mass, prepupal-to-pupal mass loss, prepupal fat content, duration of larval period, and adult longevity. Males and females differed in all studied life-history traits except adult mass. We conclude that density and temperature and their interaction-related effects during larval development considerably affect BSF larval life-history traits. Therefore, these effects should be carefully considered when planning for insect mass rearing.

Asymptotic estimated digestibility, a new indicator of black soldier fly (Hermetia illucens) conversion efficiency in relation to larval density

“…Similar adverse effects of density on survival or growth have been reported in other insect species such as Drosophila melanogaster (Henry et al, 2020), Musca domestica (Kökdener and Kiper, 2020) or Tenebrio molitor (Deruytter and Coudron, 2022). Impaired larval DM content observed in the present work at high density suggests that limited access to feed caused BSFL to use their body energy resources by oxidising their fat reserve (Opare et al, 2022). However, FCR (dry to fresh) was improved by increasing density down to an asymptote, indicating that BSFL performance as a group outweighed each individual underperformance.…”

“…Life history traits values obtained were consistent with data from the literature on chicken feed: Liu et al (2019) reported survival rates between 40 and 93% and Gold et al (2018) summarised that prepupal FM could range between 99 and 184 mg. Larval DM content were in the range of 17.9 to 38.8% reported by Bosch et al (2020). In the present study, high areal density caused stronger competition for feed resources, hence lower survival rate and individual FM and DM gain, as already observed (Brits, 2017;Jones et al, 2019;Opare et al, 2022). Dead BSFL could not be visually detected after seven days of feeding and were presumably consumed by other larvae or decomposed into the substrate.…”

High larval densities and high temperatures lead to a stronger immune response in the black soldier fly

“…Previous studies on larval density involving the larvae of economically important black soldier fly (Hermetia illucens, BSF) have shown that high larval densities have detrimental effects on central life-history traits such as prepupal mass, pupal mass, adult mass, and development time (Barragan-Fonseca et al, 2018;Jones and Tomberlin, 2019;Opare et al, 2022). However, BSF larvae are generally regarded as quite unsusceptible to diseases, and it has been suggested that they could inherently possess innate resistance to harmful microorganisms (Joosten et al, 2020).…”

Chronological and Carbohydrate-Dependent Transformation of Fatty Acids in the Larvae of Black Soldier Fly Following Food Waste Treatment

“…The longer development time of the current larvae than the previous studies [ 13 , 14 , 15 ] could be attributed to the differences of experimental temperature and complexity of the food waste. Opare et al [ 35 ] reported that high temperatures of 27–30 °C resulted in shorter larval development time than a low temperature of 23 °C. The current experiment was conducted at the ambient temperature of 22–26 °C, which is lower than the reference temperature of 26–27 °C [ 13 , 14 , 15 ], thus contributing to the longer development time.…”