House Fly Inhibition by Black Soldier Fly- How Do They Do it?

In past posts, I mentioned one of the cool biological aspects of the BSF is its ability to reduce house fly populations associated with wastes being digested by BSF larvae. One of the first papers to discuss this observation was by Dr. Sheppard way back in the 1980s. 

Bradley, S. W., and D. C. Sheppard. 1984. House fly oviposition inhibition by larvae of Hermetia illucens, the black soldier fly. Journal of Chemical Ecology 10: 853-859.

For this post, I wanted to review this paper real quick and then speculate as to how BSF might be suppressing house fly populations. Maybe it will lead to some cutting edge research in another persons lab? At minimum, it will give you some nice science trivia you can bring up at your next dinner with friends (of course- it will depend on the friend).

Synopsis: This study was conducted in the laboratory. Basically, they collected wild house flies and placed them in a cage with several oviposition (egg-laying) options. Some contained chicken manure with larvae (late instar- about 1.5 cm in length... so quite big) at various densities while others were controls (chicken manure without larvae). They also conducted this experiment with a lab house fly colony. They examined the number of eggs laid in the substrates 30 minutes, 2.5 hours and 24 hours after exposure. 

Summary: The big news- BSF reduced house fly oviposition in the manure.  They determined if you allow BSF larvae to "work" the manure for more than 30 minutes, house fly oviposition in the substrate can be reduced by 60% or more depending on the density. In the case of strain (this is very important), the wild strain did not oviposit in the manure 2.5 hours after introducing the BSF larvae at the highest density. However, the house fly strain from the lab did continue to do so. So why is this important? Great question- my thought is you can select for house fly strains that will not avoid BSF. 

TAKE AWAY MESSAGE: Just because BSF larvae are known to reduce house fly oviposition in a substrate does not mean you should depend on the BSF solely for reducing your house fly population. Over time, if you are not taking other measures to reduce house fly numbers, house flies can adapt to a given environment. This can be bad for two reasons (off the top of my head); 1) house flies compete with BSF larvae for resources which could impact your production, and 2) you do not want to breed house flies that might disperse from your facility and end up in your neighbor's home. This outcome would be bad as well- as you can imagine.

So- How do BSF reduce house fly attraction/oviposition in a substrate?  Here are two ideas:

1. BSF larvae kill E. coli and other bacteria in the resource. House fly larvae utilize these bacteria for their nutrition. If they are removed- they have nothing to consume, which prevents their development (check out previous posts on reduction of E. coli by BSF larvae)

2. BSF outcompete house fly larvae:  BSF larvae, as you know, are voracious feeders; it is possible, BSF larvae consume the waste faster than house fly larvae. This could mean if your BSF larval population is at its optimal level- house flies will never be able to develop in the waste as they are unable to consume enough resource to do so.

Final thoughts- BSF larvae do so much with regards to reducing house fly populations; however, you need to be conscience of their density as well as use other means to suppress house flies (help the BSF out- use a fly swatter).  

​As always, I hope this information is useful and you enjoyed the read. Good luck and happy BSF farming!

Author

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