Digestion of Three Waste Streams by the Black Soldier Fly- A Novel Waste Explored

One thing I always enjoy is reading papers published by graduate students. The paper to be discussed today is by Zhongyi Liu (Jay) and his colleagues out of New Zealand. I had a chance to communicate with Jay a few times over the past year or so. And, I truly appreciate his enthusiasm for working with the BSF.  I am not sure if this is his first paper or not- but congrats, Jay! Job well done. I am glad this paper came across my desk today.

The study is a straight forward life-history study of the BSF when grown on three waste streams. Two wastes are common in such studies (e.g., brewery waste and pig manure), while the third I believe is fairly unique (e.g., semi digested grass). The publication information is:

Liu, Z., M. Minor, P. C. H. Morel, and A. J. Najar-Rodriguez. 2018. Bioconversion of three organic wastes by black soldier fly (Diptera: Stratiomyidae) larvae. Environmental Entomology.

The treatment of most interest to me was the "semi digested grass". This material was not defined in the manuscript (based on my reading- apologies if I missed it) so I am not sure of its composition or how it was produced. I looked up the supplier, and it appears to be a producer of free range lambs. 

The development of BSF was compared across these treatments as well as a the semi digested (e.g., broll- wheat bran and wheat flour).  I have to admit, broll is a new term for me.  Based on information in the study, and new to me, this material is fed to chickens as a feed. This material is the standard for producing BSF used in the primary lab affiliated with this study.

Basic parameters of BSF growth were measured, including survival, development time, larval weight gain, development rate (weight/time), and prepupal dry weight.  There were definitely treatment effects- especially for the semi digested grass (massive amounts of time to develop- 70 d vs 14/17 d on other treatments). Other measures were significantly lower for grass-fed larvae (interesting term use as most recognize its use with livestock production) including prepupal weight being 50-75% less. 

Other factors measured included protein and fat content- this result is interesting as the protein content was comparable across treatments (40-50%), while fat was significantly lower for those reared on the semi digested grass (5% rather than 17% or greater). The fat content in the manure-reared prepupae was low (based on my experiences) at 17%. 

The authors also did a meta-analysis across studies- something I will not dive into here; but, a topic you might consider reviewing to gain perspective across studies.

The authors conclude the semi digested grass is not a suitable resource for producing BSF. However, I would encourage some restraint in closing the door on such opportunities. My reasoning being, 1) it worked (just not to the level produced for other resources), and 2) with what we are learning about the microbiome, I suspect there are steps that can be taken that will allow for enhancements in the system to allow more optimal production levels.

Author

Jeffery K. Tomberlin, PhD, Supporter of Graduate Researchers
Director, EVO Conversion Systems
​Twitter: @FliesFacility