1	Keeping BSF Larvae Warm in Winter ESR LLC 317 North Bridge Street Washington, La 70589
2	As Temperatures Drop The larvae of the black soldier fly have an amazing ability to dispose of putrescent waste. But as the temperature drops below 21˚C, their ability to digest waste progressively grinds to a halt, and if they should freeze, they die. This tropical fly larva needs to be sustained at temperatures above 30˚C if it is to continue to digest putrescent waste at the standard rate of roughly 15 kgs per m²of unit surface per day.
3	Strategy To bring bioconversion units indoors during winter would be costly, and to equip them with heating coils may not be necessary. The strategy set forth here involves nothing more than placing a styrofoam sheet on top of the larval residue to retain the heat generated by mesophilic bacteria and by the movement of the larvae themselves. If this heat is not allowed to escape, the
4	Styrofoam Panel temperature on the surface of the residue easily exceeds 35˚C. The first picture in the following slide shows the styrofoam panel in place, while the second picture shows the active mass of larvae underneath.
5	Styrofoam Sheet
6	Minus 1˚ C When these two pictures were taken, the outdoor temperature in early January had dropped to minus 1˚ C. When the styrofoam sheet is lifted in the early morning, a cloud of water vapor rises up from the warm mass of larvae in full activity. Imagine such a vigorous and healthy colony of tropical larvae right in the middle of winter.
7	Larvae in Full Activity
8	Larvae @ - 1˚ C
9	Eggs Laid in October The larvae we see in this unit all came from eggs laid in October when adults females were still active. The density of larvae in Jan/Feb appears to be as high as at any other time of the year. Likewise, the ability of these larvae to dispose of putrescent waste appears to be as great as at any other time of the year: a 35-pound pumpkin dispatched in less than 24 hours, a 5-pound bag of rice completely devoured within 45 minutes,
10	The Food Waste of 4 Households the daily food waste of a typical household digested within 2 hours! Four households are providing food waste for this bioconversion unit of approximately 6 ft² of surface area. No one within our neighborhood has complained of odors associated with the unit, and the unit at all times during the year is virtually free of houseflies and other filth-bearing flies. It is hard to imagine a simpler or more effective way
11	Vermi-Composting of diverting food waste from landfill. With a 95% reduction in the weight and volume of the food waste, only the greatly reduced larval residue must be transported once a year to a centralized composting facility. Since one man within our neighborhood has extensive experience in vermi- composting, we intend to set up a small vermi- composting unit to process on site the remaining larval residue.
12	BSF-Composting Note that in all of the pictures presented so far, we see residue of a high cellulosic content, such as the thin outer skin of a pumpkin. This material forms a wonderful substrate for earthworms and redworms. A perfect partnership is created whereby BSF larvae digest fresh food waste, something earthworms and redworms cannot do, while these worms in turn degrade and digest cellulose, something BSF larvae cannot do.
13	Total Bioconversion Vermi-composting and BSF-composting work hand-in-hand in disposing of just about all types of putrescent waste generated by human activity. The ultimate residue from this partnership forms the finest organic fertilizer, and it represents far less than 5% of the original weight and volume of the food waste. These two small creatures work in perfect complementarity in enabling us to divert virtually all food waste from landfill.
14	BSF Larvae in Winter
15	Temperature Graphs The following graphs plot daily temperature readings recorded both outside the unit and underneath the sheet of styrofoam. Note that outside temperatures may fluctuate dramatically, but the temperature underneath the styrofoam sheet remains relatively stable. The difference in temperature between inside and outside the unit can exceed at times 82˚F or 45˚ C.
16	From January 14 to 16, 2003 High outside temperature readings are explained by the fact that the unit was situated in full sun. If the internal temperature should rise above 100˚ F or 37.8˚ C, the larvae begin to crawl out from underneath the styrofoam. Therefore, it is best that the styrofoam sheet not cover the entire surface of the residue. This allows the larvae to migrate toward the cooler edges of the styrofoam without having to evacuate the unit to cool down.
17	January 14, 2003
18	January 15, 2003
19	January 16, 2003
20	Regular Feeding The last three graphs closely resemble one another. But the following graph shows a big reduction in several internal temperature readings. How to explain this difference? In order not to disturb the internal temperature by opening and closing the unit, we refrained from introducing waste on Jan 15^thand 16^th. On the 17^th, it appears that the ability of the larvae to generate heat was diminished, and right before noon we were
21	Hungry Larvae obliged to resume feeding in the usual manner. Fortunately by 6:00 PM, the temperature within the unit was fully restored. It would appear, therefore, that the larvae play a significant role in generating heat within the unit, and they need to be fed on a regular basis throughout the winter months.
22	January 17, 2003
23	January 18, 2003
24	Winter Temperatures In order to better understand the winter conditions in south Louisiana, let us look at the following graph that plots the daily maximum and minimum temperatures from October, 2002 to February 2003. In no way are these the coldest winter temperatures in the United States, but they are far from ideal for a tropical insect.
25	From October to March
26	Insulated Bioconversion Units As we move north from Louisiana and into the more temperate areas of the United States where winters are far colder, it may be necessary to wrap the outside of the larval unit in insulation. The new round bioconversion unit designed by ESR should be far easier to insulate than the rectangular unit depicted in this experiment. With insulation on the sides,
27	BSF in Eugene, Oregon with insulation on top of the residue, and with mesophilic bacteria and larvae generating an ample amount of heat from within, the larvae should be able to thrive out-of-doors even during the harshest winters. Anne Donahue, a compost specialist in Eugene, Oregon, reports the presence of active BSF larvae during the winter months in many of the vermi-composting bins in her area.
28	BSF in Eugene, Oregon Even though winters in Oregon are far colder than in Louisiana, as we observe in the following graph, BSF larvae still manage to thrive quite nicely there in outdoor worms bins throughout the coldest winter months.
29	From October to March
30	Conversion Rate Drops in Winter During the warm summer months, the conversion rate of fresh food waste into fresh larvae runs as high as 20%. But during the cold winter months, this conversion drops to less than 5%, in spite of the fact that the larvae digest roughly the same daily quantity of food waste per ft² of unit surface area. Under ideal summer conditions, it takes about two weeks for newly hatched larvae to reach their mature prepupal form, but during the cold of winter,
31	Factors Constraining Maturation this two-week period extends to three or four months. What are the factors that inhibit larval maturation in wintertime? In the case of this experiment, the larvae received during the winter months roughly the same amount of nutrients as during the summer months, and yet their growth and development were severely constrained. If adult black soldier flies must inherit a large fat body from the larval stages in order
32	What Triggers Maturation? to complete their life cycle as adults (adults do not eat), and if larvae during winter must continually draw upon their stores of fat in order to keep warm and survive, perhaps the large majority of larvae during the winter never acquire sufficient fat to reach maturity. Or perhaps, the failure to reach maturity is part of a winter survival mechanism that is not directly related to fat content but to a simple drop in temperature at the onset of winter. Imagine mature prepupae that dig down a
33	A Single Generation of Larvae few inches into the soil, and in so doing, they still remain quite vulnerable in the case of a hard ground freeze. But a pocket of actively feeding larvae within a clump of rotting vegetation, for example, might have the means to generate their own heat and easily survive the same. As long as they are battling cold, perhaps they do not mature in spite of an adequate fat body content. If this is the case, a single generation of larvae, under the right
34	Larval Maturation conditions, might sustain a BSF disposal unit throughout the entire winter. We call upon entomologists to research the question of larval maturation: is it related more to temperature than body fat content? is it part of a winter survival mechanism? just how far can larval stages be extended and under what combination of conditions? and ultimately can a single generation of larvae sustain a bioconversion unit for
35	Full Access to Food Waste indefinite periods of time? As long as the surface of the unit remains uncovered in winter, the larvae are forced to remain far below the surface to avoid the cold. Since any food waste deposited on the surface of the unit can only be approached from underneath, the larvae have limited access to the food waste. But with a residue or larval cover, the larvae have full access to the waste, and therefore, the speed at which the waste is consumed appears to
36	Ideal Feeding Conditions be higher than at any other time of the year. The styrofoam sheet creates a warm, dark, sheltered environment that apparently represents ideal feeding conditions for the larvae. Of course, styrofoam is not the only material that could be used, and it is easy to imagine larval covers made out of many other types of insulating materials. After only one week of use, the styrofoam sheet used in this experiment was riddled with hundreds of holes and
37	Larval Covers had to be discarded. Larval covers that come wired with temperature sensors and transmitters might simplify the daily management of large on- site food waste disposal facilities associated with restaurants, schools and other institutions. Larval covers equipped with handles should be far easier to manipulate than sheets of styrofoam. However we fabricate them, larval covers may become an essential element of disposal units in cold climates.
38	Far Easier Than Previously Imagined If BSF larvae are able to generate their own heat throughout the winter, and if at the same time they are able to extend their life cycle until more favorable conditions return in spring, then the management of BSF larvae becomes far easier than anyone had previously imagined: no need to shut down BSF disposal units during winter, no need to supply them with eggs, no need to cut back in winter on the amount of food processed, no need to supply heat
39	Conclusion to keep larvae warm. If disposal units and larval covers are well insulated, then BSF technology could be introduced to some of the coldest regions of our planet. If so, the supply of eggs to such extreme areas will become an important technical issue, and all aspects of larval maturation must be researched in a definitive and conclusive manner.
40	Conclusion Thousands of years ago we domesticated bees and silkworms, and closely studied their behavior ever since. In using BSF larvae to dispose of waste, we have before us the possibility of fully domesticating a third insect, feat that could be of immeasurable benefit to our planet. Surely this merits many years of intense research, since we have just begun to appreciate the seemingly endless potential of this remarkable insect.