Commercial Production of BSF |Tracking Adult BSF Emergence : The Life and Times of BSF (Black Soldier Flies)
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Commercial Production of BSF |Tracking Adult BSF Emergence

by Terry Green on 10/07/14

Commercial farming of BSFL (Black Soldier Fly larvae) grown off of food scrap requires accurate record keeping and monitoring  for optimal BSF production year round. An important aspect in keeping a colony productive involves culling off a portion of the daily BSF prepupae harvest for maintenance of the insect colony. For optimal year round yields, the emergence of new adult BSF should be monitored on a regular basis in propagating new offspring. Pupation and emergence varies considerably depending upon the temperature harvested prepupae are stored at in transforming into adults (see The Effect of Temperature on Emergence of Black Soldier Flies). This blog describes a simple and rapid method of  monitoring adult emergence.

You might be asking, why monitor adult emergence? Why is this necessary? Simply put,  monitoring provides guidance and a record based upon the operating environment of your plant on how long to retain pupae set aside for propagation of the colony. Once pupae emerge from their puparia as adults, leftover puparia shells can be recycled as feedstock for the colony or, alternatively, processed and marketed as a commodity byproduct (chitin/chitosan stock used in pharmaceuticals, medicine, paint stocks, certain foods, etc.).

Without tracking adult emergence,  pupae not yet having emerged as adults could be wasted as stock set aside for propagation gets discarded. The premature loss of adults in this latter case will result in a sharp falloff in future offspring and subsequent loss in harvested larvae.

Having a record of past emergence statistics can also be informative of any changes occurring in the colony at the plant facility. A sharp drop off in emergence could foretell ahead of time, for example, that a problem in propagating fertile BSF adults needed in maintaining a productive colony is occurring. It can serve as an early warning sign of a problem needing correction in the management of the colony.

It is simplest to score the emergence of adults as a ratio of the number of adults emerging relative to  total prepupae set aside for maturation into adults on a daily or weekly basis. Adults generally emerge within 30 days at the latest from the time they begin pupating when set aside and stored around room temperature ~72 F (~21 C).

Figure 1 summarizes the differences in appearance of BSF from pictures taken at the pupa stage (Fig. 1a), a picture of the puparium shell left behind after emergence (Fig. 1b), and that of an adult BSF having emerged from its puparium (Fig. 1c).  The head section of the BSF breaks away from the remaining puparium shell during emergence leaving behind the empty shell which makes it very easy in sampling prepupae set aside for propagation to determine at any given time the percent emergence of adults. Simply draw at random a small sample of prepupae set aside for pupation and count the number of empty shells and divide by the total number of puparia sampled.

image of pupa, empty puparium and adult BSF
Fig. 1. Picture of pupa, empty puparium shell and adult BSF. Fig. 1a, pupa pupating before emergence as adult BSF; Fig. 1b, empty puparium shell; and Fig. 1c, adult BSF following emergence from puparium. © Copyright 2014, Terry Green, All rights reserved.

Fig. 2 illustrates this simple technique in tracking adult emergence. In this instance, at the time of sampling the emergence rate had reached 37%  in the lot sampled indicating that this particular lot of prepupae set aside for propagation of the colony should be held longer for full emergence rather than
image ofBSF pupa and puparia empty shells
Fig. 2. Counting emergence of adult BSF from sample of prepupae set aside for propagation of BSF colony. Sample of puparia drawn in sample are separated into intact pupa still pupating and empty puparia shell shells remaining from those left behind by adults having already emerged from their puparium. The percent emergence is determined by dividing the number of empty shells remaining by the total number of puaria drawn in the sample x 100. Left, intact pupa still pupating; Right, empty puparia left behind by adults having already emerged from their puparia. © Copyright 2014, Terry Green, All rights reserved. 

The larger the sampling size, the more certain the evaluation on the emergence rate will be as a general rule. Assuming random statistical sampling, it is reasonable to estimate that the certainty of the estimated emergence rate is approximately 1 divided by the square root of the sample size x 100. So, for example, in counting 100 puparia drawn at random, the evaluation of emergence should be roughly accurate to within  ±10%.

Higher sampling sizes will provide better data, but a sample size of 100 puparia as a general rule is adequate in tracking adult emergence. In a well-run operation the adult emergence rate should reach 90+% of prepupae set aside for propagation purposes.

Check back for more to follow on the management and strategies in scaling up BSFL production.
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being discarded or recycled into other byproducts.


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