Lights, Camera, Action- How Do Black Soldier Flies Respond to Light? A Possible Answer

There is  a lot of discussion with regards to how light impacts BSF mating. We all recognize that sunlight is the best light source to stimulate mating in adult BSF; however, given the inconsistency of sunlight throughout the year in various locations around the world, a lot of effort has been invested to develop artificial lights for mass-production of BSF in culture. In fact, there are a number of examples on the market today- some of which you probably read about through this blog.  To date, artificial lights stimulating BSF mating are pretty good. Using them results in about 65% of the mating observed when using direct sunlight. Now, that might not sound like good results but if you consider the variability and issues occurring when sunlight is not optimal- these numbers are in fact impressive. At minimum, you are getting consistent mating in doors (albeit other conditions have to be optimal as well, such as humidity).  

So- how does this dialogue relate to the title of this blog post? Well, a really nice article was published recently in BMC Biology on blow flies. These are the metallic green or blue flies you see associated with decomposing vertebrate remains. Of course, these are not the flies you want to be reproducing in your BSF units; however, we might be able to learn a bit from their biology and eventually adapt it to optimizing the mass production of the BSF.  The article in question is:

Eichorn, C., M. Hrabar, E. C. Van Ryn, B. S. Brodie, A. J. Blake, and G. Gries. 2017. How flies are flirting on the fly. BMC Biology 15: 2.

What I found most interesting about this article is the response of the adult blow fly to light patterns resulting from the wing beat of the female. They determined males actually respond to a set frequency exhibited by the female.  They even determined they could use flickering light at a set frequency to attract males.

So- why is this important for the BSF and its mass production? Well, I am not sure I have a straight forward answer. But I do have questions with potential answers for you to think about as you develop your colony.

1. Could you use light frequency to segregate flies? So why would you want to do this? My thought is if you have a cage of BSF and mating occurs during the first two days, you could use light frequenting to attract males away from females- isolate them. Doing so could allow you to amp up your mating success by removing females that are potentially already mated- or males that have mated as well. You could infuse your colony with fresh individuals and enhance mating success. Of course, this hypothesis is purely based on the assumption that males/females typically mate once.

2. Optimize light to increase frequency strength. If we can determine the light frequency that enhances the pattern emitted by the female wings, we could potentially allow males to "see" females better thus allow for greater mating success.

3. Shift light patterns during day. This actually gets at the idea that there is an ideal time during the day for males (virgin) to mate. Outside of this window is restricted to males that are desperate for female attention either due to their being old or not virgins (i.e., already mated and thus have nothing to offer). So, you could restrict optimal light intensity during peak periods of the day (most likely between 8-12) so that only active males (virgin) are seeking females. Doing so could reduce the likelihood of unacceptable males (unable to fertilize females due to previous mating) trying to mate with females.

4. What is the proper angle of light in a cage?  If wing beat frequency in combination with light is important, determining the proper angle of artificial lights in a cage is critical. If your angle is off a few degrees, males may not see females flying by- and thus miss the opportunity to mate.

These are a few ideas from my brief brainstorming session on this paper. In the end- we should always be looking at other insect systems to see what we can learn from them and then apply to the BSF..... so keep reading... and please, share your thoughts!

Author

Jeffery K. Tomberlin, PhD, BSF behavior specialist
Director, EVO Conversion Systems
​Twitter: @FliesFacility