Black Soldier Fly Larvae- Composter Extraordinaire: Part 4- Conversion of Food Waste and Potential Use of Residue as Fertilizer

Good news- a two for one post today! I hope you all have a great weekend. As a FYI, I am traveling next week, so my posts might be delayed a bit.  

Here we go......

Several studies have examined the ability of the BSF to convert food waste to protein and fat. But, before I delve into these studies and their findings, I want to remind you all to really consider how you define the food waste you provide your larval BSF. Remember, the BSF, much like you, is impacted by the food they eat. For the BSF, too much protein and the larvae,

1. grow much slower
2. suffer higher mortality
3. do a poorer job of converting waste to insect biomass
4. which results in other pest insects coming into the system

 
With regards to carbohydrates, if in plant form, the BSF does a pretty spectacular job handling the waste.
 
What is known about BSF reducing food waste?
 
There are a few studies on this topic- and it seems more and more are being done each year, which is great. The more we know, the more we can determine the dependability of the BSF to function in such a capacity. 
 
The study I will review is the following by Trinh Nguyen when she was a MS student at the University of Windsor in Windsor, Canada.
 
Nguyen, T. T. X., J. K. Tomberlin, and S. Vanlaerhoven. 2015. Ability of black soldier fly (Diptera: Stratiomyidae) larvae to recycle food waste. Environmental Entomology 44: 406-410.

Overview:  This study examined the ability of the BSF to convert several food types. These included, poultry feed, liver, manure, kitchen waste, fruit & vegetables, & fish. The authors examined the life history traits of the BSF (larval weight, development time, nutritional value of the prepupae collected) as well as the nutritional value of the waste itself.   

Synopsis: As expected waste type impacted BSF development. Larvae provided fish developed slow, while those provide fruits and vegetables grew fast.  Furthermore, waste type impacted conversion rates of the BSF with manure having the lowest level of reduction. And, with regards to quality of BSF prepupae produced, nutritional value varied depending on what the larvae were fed.
 
Conclusion: This study demonstrates a point I have made in several previous blogs. What you feed your larvae impacts all parameters of your operation regardless if you are big or small. Keeping records of the materials you provide larvae in conjunction with production are critical for consistent output. As a sidenote, such records also allow you to troubleshoot when an issue comes up, such as larval die-off, delayed production, or small larvae produced (just a few examples).
 
I hope the review of this study proves useful. I encourage you all to read the papers and draw your own conclusions. If you have questions, post them on the blog or email me directly. I am here to help.  J
 
Now- one more thing… once you have the system down and you are producing larvae….
 
What do you do with the remaining food waste after digestion?
 
One potential path is the development of the residue as a fertilizer. I had done some preliminary work a while back on this potential application, and I found that the material is still relatively “hot” and probably needs to be composted or diluted with other organize matter (i.e., leaves, straw, etc) to reduce the Nitrogen content. I suspect this is residue specific and that what I found was really just because of what I was working with at the time (dairy manure).
 
A study you might find interesting on this topic is:
 
Choi, Y., J. Choi, J. Kim, M. Kim, W. Kim, K. Park, S. Bae, and G. Jeong. 2009. Potential usage of food waste as a natural fertilizer after digestion by Hermetia illucens (Diptera: Stratiomyidae). International Journal for Industrial Entomology 19: 171-174.
 
Overview: The authors reared BSF on food waste. With the residue, they initially conducted a chemical analysis and compared it with commercial fertilizer. They then used the residue as a fertilizer for cabbage.
 
Synopsis:  The authors indicate the BSF residue is not different than the commercial fertilizer examined in this study (Table 1); however, if you look at the nitrogen amounts, it does appear the BSF residue has a significantly higher level than the commercial fertilizer. They determined there were no major differences in nutrient composition of cabbage grown with either the food waste residue produced by BSF as a fertilizer or the commercial fertilizer. Table 2 in the paper provides these data. They also conclude plant growth was comparable between treatments (cabbage with BSF residue and cabbage with commercial fertilizer).
 
Conclusion:  Data from this study look promising. However, additional research is needed to see if results remain consistent across crops. Also, given the link between flies and pathogen movement, it would be good to determine if BSF residues pose such a risk.
 
Check out this paper on intestinal bacteria of BSF reared on food waste:
 
Jeon, H., S. Park, J. Choi, G. Jeong, S.-B. Lee, Y. Choi, and S.-J. Lee. 2011. The intestinal bacterial community in the food waste-reducing larvae of Hermetia illucens. Curr Microbiol 62: 1390-1399.
 
As always, I hope this information is useful to you. Until next time....best of luck and happy BSF farming!

Author

Jeff Tomberlin, PhD, BSF caregiver
Twitter: @FliesFacility
Director, EVO Conversion Systems
evoconsys.com