Winter is Fast Approaching in Many Places- What Will I Do with My Black Soldier Fly Larvae Growing in my Compost?

Great question (in the title)!

As you know, BSF are very sensitive to temperature. Adults will easily succumb to temperatures below 27C (80F)- well, succumb = not mate, which is bad if you are trying to maintain a colony.

The larvae on the other hand are a bit more tolerant of "colder" temperatures as they can generate quite a bit of heat in their maggot mass. However, this ability doesn't mean temperatures below 10C are a good thing as such experiences will slow down larval growth and consequently, protein production and biomass remediation.

There are few papers (one prior to this post) that I am aware of that examine the relationship of temperature to BSF biology. 

Holmes, L. A., S. L. VanLaerhoven, and J. K. Tomberlin. 2016. Lower temperature threshold of black soldier fly (Diptera: Stratiomyidae) development. Journal of Insects as Food and Feed 2: 255-262.
 
I believe I mentioned this paper in a previous post. So not to be redundant- I will only provide a brief review. The premise of this study was to determine the lower temperature threshold of BSF during different immature stages. For eggs, a temperature between 12-16C was determined to be the lower threshold- basically, when eggs experienced temperatures between this range they did not hatch. What was really cool with this study was eggs could be stored for longer periods of time when approaching the lower threshold- they could actually could be stored for two weeks before hatching! So there is a sweat spot with temperature and egg storage. Finding it for your population could be useful if you want to store eggs. Temperature threshold for larvae was a bit higher- around 16-19C. 

Now- please keep in mind these results are population specific. Data generated in this study are for a population from Texas/Georgia, USA.  

But this paper is not the reason for my post. As I indicated, I believe I covered this paper in a  previous post. The main reason for today's post is the following paper:

Spranghers, T., A. Noyez, K. Schildermans, and P. De Clercq. 2017. Cold hardiness of the black soldier fly (Diptera: Stratiomyidae). Journal of Economic Entomology 110: 1501-1507.

These researchers examined the supercooling point and lower lethal time for prepupae and pupae of the BSF.  They determined both stages could survive cold temperatures (below -7C); however, this ability was really dependent on what the larvae were fed. Those provided a more nutritious resource demonstrated more tolerance than those without good nutrition.

Basically- the larvae need to be "strong" to make it through the winter. 

Now- please keep in mind these results are population specific. Data generated in this study are for a population from Texas/Georgia, USA. Wait... didn't I just say this? Why yes I did but it was for the previous study. Interesting point, the same statement needs to be made for this paper as they indicate the specimens they worked with originated from the same Georgia colony. Regardless, I am sure you get my point- each study is population specific so take the results with some reservation as they might not apply to your population of BSF.

Moving on.... :)

Another important point I gleaned from the paper- BSF larval ability to survive low temperatures was also dependent on time. Those with the best nutrition could survive for three weeks at these low temperatures.

So with this in mind, you can experience cold temperatures in your compost or BSF digester and not lose your larvae; however, how you take care of them will be a major factor (good nutrition).  

Feed your larvae well- especially in the winter (lots of carbohydrates, manage water in digester, moderate protein) so that if you do experience low temperatures you do not lose your larvae! 

As always- I hope this information is useful. Best of luck and happy BSF farming.

Author

Jeff Tomberlin, PhD, BSF nutritionist
Twitter: @FliesFacility
​Director, EVO Conversion Systems