How Do I Get Black Soldier Flies to Lay Eggs in a Location of My Choosing? Hint- Check Your Microbes!

One area we know very little about with regards to the BSF is the role of microbes in their biology and behavior.
 
Yes- we know BSF larvae can kill some pathogens, such as E. coli or Salmonella.
 
Erickson, M. C., M. Islam, C. Sheppard, J. Liao, and M. P. Doyle. 2004. Reduction of Escherichia coli O157:H7 and Salmonella enterica Serovar enteritidis in chicken manure by larvae of the black soldier fly. Journal of Food Protection 67: 685-690.
 
And yes- we know BSF larvae produce antimicrobials. 
 
Park, S.-I., B. S. Chang, and S. M. Yoe. 2014. Detection of antimicrobial substances from larvae of the black soldier fly, Hermetia illucens (Diptera: Stratiomyidae). Entomological Research 44: 58-64.
 
But outside of these few papers, and maybe a couple more, we know practically nothing about the associated microbial ecology and how it plays a role with the BSF biology. Are there ways to manipulate microbes so that they do not compete with BSF, or make BSF larvae sick (die-off in larval communities is a real thing- believe me)? 
 
One study has examined the role of bacteria in regulating oviposition (egg-laying) behavior of the BSF.
 
Zheng, L., T. L. Crippen, L. Holmes, B. Singh, M. L. Pimsler, M. E. Benbow, A. M. Tarone, S. Dowd, Z. Yu, S. L. Vanlaerhoven, T. K. Wood, and J. K. Tomberlin. 2013. Bacteria mediate oviposition by the black soldier fly, Hermetia illucens (L.), (Diptera: Stratiomyidae). Scientific Reports 3.
 
Overview: As many of you have noticed, BSF females, when searching for an oviposition site, will drag the tip of the abdomen along the surface of a substrate.
 
https://www.youtube.com/watch?v=y1oWApsc_ts (video of BSF dragging ovipositor)
 
The tip of the abdomen contains the ovipositor, which is used to lay eggs. Once a site is located, she will extend her ovipositor out and begin dumping eggs at that site (think of the Queen alien in the second movie of Aliens with Sigourney Weaver laying her alien eggs: https://www.youtube.com/watch?v=mOkPNZHEbDI).
 
The BSF female ovipositor is loaded with sensors that allow her to determine just the right spot for her to lay her eggs. These sensors detect a host of characteristics ranging from moisture and light to odors.
 
In fact, bacteria associated with the food resource release many of these odors. These odors contain loads of information about the substrate the female BSF is considering as an oviposition site, such as the presence/absences of vital nutrients, pathogens, or other BSF eggs or larvae.
 
This study examined the role of bacteria isolated from BSF eggs as well as the offspring of other competing insects common in decomposing material, such as blow fly and beetle larvae.
 
Synopsis: This study demonstrated that a couple of factors related to bacteria regulate BSF egg laying. 
 

1. Bacteria concentration: Yes- concentration is considerably important as it indicates if the community is appropriate for BSF egg development. Too much or too little and the bacteria could be pathogenic or unable to provide essential nutrients to the BSF larvae, respectively.
2. Bacteria species: Different bacteria yielded different results. In some instances bacteria from the BSF resulted in attraction and oviposition by the BSF. This goes back to my last point- each species represents different things (e.g., friend or foe) to the BSF.
3. Origins of the bacteria:  You should definitely remember this point- bacteria species isolated from different substrates/resources- even if identified as the same species- are quite unique from one another. That’s right- even if the same species, they can genetically be very different. My reason for emphasizing this point is if you plan to use bacteria to enhance egg-laying by the BSF, you want to isolate the bacteria either from BSF eggs or the substrate in which the larvae develop.  This point also applies to bacteria isolated from competing species, such as other flies or beetles. These bacteria most likely signal the presence of a competitor, which could inhibit egg-laying by the BSF.
4. Strength in Numbers: This study determined that individual bacteria can be used to induce egg-laying by the BSF; however, greater responses were determined when dealing with communities of bacteria. So what is that? Well, bacteria respond to their environment. When you rear an individual bacteria species by itself, it faces no competition and doesn’t reap the rewards of the activities by other bacteria present. Think about it- when you go to the zoo, does an animal held in captivity behave like it does in nature? Probably not- so the same is true with these bacteria; they need the community involvement to exhibit behaviors (e.g., odor production) commonly occurring under natural conditions.

 
Conclusion: There are ways to enhance oviposition- some high tech, such as isolating and culturing bacteria as done in this study. However, there are other methods you might consider: 1) place BSF larvae in the container where you want BSF adults to lay eggs; 2) when replacing your oviposition substrate, mix waste from the old container used for collecting eggs with the fresh material (should enhance attraction of BSF adults); 3) prevent females from accessing the substrate. Maybe cover the substrate with a screen and place cardboard blocks on top- make the female lay her eggs in the cardboard. By doing so- you can quantify egg production much better.
 
Well- I hope this information helps and is of interest to you. As always, best of luck and happy BSF farming!

Author

Jeff Tomberlin, PhD,BSF/microbe sparring partner
Twitter: @FliesFacility
Director, EVO Conversion Systems