Black Soldier Fly Larvae as a Tool for Managing Animal Waste and Providing a Food Source for the Aquaculture Industry

Black Soldier Fly Larvae as a Tool for Managing Animal Waste and Providing a Food Source for the Aquaculture Industry

Summary

Results of our 8 week rainbow trout feed trail suggests fish will grow on a black soldier fly- based feed and their flavor is not affected. During the summer of 2008 we grew black soldier flies in an outside facility on a dairy farm near Twin Falls, Idaho. We were only partially successful at harvesting prepupae from our systems. The poor harvests were attributed to the cold night time temperatures. Given our results from the farm study raising black soldier flies in Idaho will most likely require a temperature controlled environment.

Objectives/Performance Targets

The following is an update for each objective of the proposal:

Objective 1) 20 week rainbow trout feed trial using prepupae

Task 1) Grow prepupae for feed.

Idaho State University researchers grew the omega-3-fatty acid enhanced prepupae required for the fish feed trial. Researchers at Texas A&M University grew the (non-enhanced) prepupae required for the feed trial.

Task 2 and 3) Conduct feed trial and sensory analysis of the fish

Black soldier fly prepupae were reared on dairy manure and enriched by supplementing fish offal to the growth medium during the last month of culture. For the fish feeding trial, a practical-type trout diet was formulated to contain 45% protein, with roughly half of the protein derived from fish meal and the remaining from soybean meal, corn gluten meal and wheat meal. Four test diets were developed by substituting 25% and 50% of the fishmeal component of the control diet with normal (BSF) or enriched (EBSF) black soldier fly prepupae on a amino acid equivalents basis (Figure 1). Dietary fat content was adjusted to approximately 20% lipid using fish oil and poultry fat to provide required levels of essential fatty acids and maintain approximately equivalent fatty acid ratios between the treatments. Diets were fed to three replicate tanks of fish per treatment (15 fish/tank, mixed-sex House Creek strain) for 8 weeks. Trout were reared in 140 L tanks supplied with 6 L/min of constant temperature (14.8°C) flow-through spring water (Figure 2). At the end of the feeding trial, three fish per tank were sampled for determination of hepatosomatic index, intraperitoneal fat ratio and muscle ratio. The muscle portion obtained was subsequently utilized for determination of proximate and fatty acid composition. Fish remaining after sampling were pooled by tank, euthanized and immediately transported on ice to a commercial fish processing facility. At the processing facility, fish were individually hand-filleted as gourmet fillets with ribs and pin bones removed. Following filleting, samples were pooled by tank and stored at -20C until shipment (approximately 1 week) to Washington State University for sensory evaluation.

Growth of fish fed the EBSF diets was not significantly different from those fish fed the fishmeal-based control diet, while growth of fish fed the BSF diets was less than those fed the control diet (Table 1). Muscle ratio was not altered by diet but control fish had significantly higher IPF than those fish fed the EBSF or BSF diets. A group of 30 untrained panelists did not detect a significant difference in a blind comparison of fish fed the fishmeal control diet as compared to fish fed the EBSF or BSF diets (Table 1). These data suggest that EBSF can be used to replace up to 50% of fishmeal portion of a practical trout diet for 8 weeks without significantly affecting growth or sensory quality of rainbow trout fillets.

Objective 2) Adapt proven methods of growing black soldier flies to dairies in Idaho

The experiment focused on testing the behavior of black soldier fly larvae under field conditions. The study was conducted on a 3,000-cow dairy located in Southeast Idaho. An unused manure separator facility was adapted for a shelter which provided shade and wind protection for the containers (Figure 3). Netting was used around the facility to reduce escapment of adult flies and provide shade and wind protection. A wooded floor was contracted with a 2 inch high border to prevent larvae and prepupae from esaping if they migrated out of the collection containers or primary containers. Three different types of containers were tested:

• Circular, 8 feet diameter and 3 feet deep container (Figure 4)
• Recycle bin (Rectangular shape with gradual slope on one side) (Figure 4)
• Smaller 3 feet diameter circular container (purchased from ESRI International LLC) (Figure 5)

The experiment was conducted in three phases

Phase 1: Larvae were grown at Idaho State Laboratory for 2.5 months. There was a delay in the summer weather so the larvae were maintained in the laboratory for a longer period of time than anticipated. To delay the development of the larvae the laboratory temperature was maintained at approximately 70 F. The farm study was started June 11 2008. Approximately 1,763,100 larvae were distributed in the three previously mentioned containers as follows:

• Large circular container = 417 Kg of bedding and approximately 1,445,742 larvae
• Recycle bin = 78 Kg of bedding and approximately 264,465 larvae
• Small circular Container = 13 Kg of bedding and 52,893 larvae

On June 27, 2008 the larvae were fed fish offal to stimulate their growth. On July 4, 2008, the first prepupae started migrating out of the containers. After a week, there was an intensive period of two weeks (July 10, 2008 to July 24, 2008) where 88% of the prepupae migrated out of the containers. After this period, the harvest of prepupae decreased dramatically.

The total quantity of manure added to the containers was 1,588 kg for the large circular container, 380 kg for the recycle bin, and 128kg for the small circular container. Larvae were fed this quantity of manure between June 11 2008 and July 28 2008. The feed was delivered every two or three days. The total amount of prepupae harvested per container was: 6.75kg for the large circular container, 3.65 kg for the recycle bin (the larvae were transferred into 4 smaller containers to permit the migration of prepupae), and 1.64 kg for the small circular container. A significant amount of prepupae were collected from the floor (1.2 kg). In total, approximately 13.3 kg were harvested from all three containers and the floor.

The average weight of a prepupae was 0.14 g. There were approximately 71 maggots in 10 g. Based on this estimate, we harvested approximately 93,990 maggots. This value represents only 5.3% of the original population. The large proportion of losses was distributed between immature and dead larvae within the containers. Very few larvae developed into flies.

The shape of the Recycle bin container did not permit the prepupae to migrate properly, therefore, on July 9 2008 the Recycle bin was divided among four of the smaller 3 foot circular containers to prevent losing prepupae. These four containers were treated as a single unit for measuring manure and prepupae production.

Phase 2 began on July 18, 2008. Additional eggs were received from Georgia, maintained for two weeks at the Idaho State University laboratory and subsequently divided into two containers: a large 8 ft circular and a smaller 3 ft circular container. Fourteen kg of manure with an estimated 407,000 larvae was placed in large circular container, and 3 kg of manure with an estimated 111,000 larvae were added to the smaller circular container. The change in the quantity of bedding was based on the observations from the first trial which suggested the larvae only feed in the top 5 cm of manure.

The migration of the prepupae in this second trial started August 31, 2008, approximately 6 weeks after the larvae were transferred to the farm. The time period from initially being brought onto the farm and migration was similar to the first trial, despite the shorter laboratory growth period; however, the harvest was much less than in the initial trial. Additionally, there was no intensive period of migration observed. This trend continued until October 8 2008 when activity stopped.

The total quantity of processed manure in phase 2 (July 18 2008 through October 27 2008) was: 1074 kg in the large circular tank and 125 kg in the small circular container. Larvae were fed this manure intermittently, based on activity level. The total weight of prepupae harvested was 122 g and 139 g in the large and small container, respectively. The average weight of the prepupae was 0.12 g (less than the first trial) or 80 prepupae weighed approximately 10 g. It is estimated, based on this weight, that only 0.4% of the prepupae migrated out of the containers.

It was hypothesized that the low yield was due to two factors: 1) the night time temperature (50 F) during the second trial approached the lower limit for the black soldier fly and 2) the larvae were not fed fish offal during the second trial.

Phase 3 The study was repeated with a large 8 ft circular container. Approximately 350,000 eggs (treated in a similar manner as in trial 2) and approximately 10.6 kg of manure was seeded in the container. This third farm trial was initiated on August 6, 2008. Only a negligible number of prepuape (71g) migrated out of the container. Despite efforts to increase the night time temperature in the facility it remained below 50 F during the predicted migration period. Given the low day and night time temperatures, the field study was concluded on November 18, 2008.

Farm data on manure consumption on a dry matter basis will be analyzed in the spring of 2009. Preliminary conclusions on raising black soldier flies from this farm study are:

• Under field conditions, prepupae are very susceptible to management issues like transfers, bedding turn over, flooding and temperature changes.
• Feeding the larvae with fish offal appeared to provide a great stimulus for growth and maturity.
• For larger container surfaces, more ramps and collector buckets are needed per unit. Under low temperatures. It is more difficult to maintain the temperature of the bedding manure especially when there is not drainage and the bedding is wet or flooded.
• Although the dark cloth container covers helped the larvae remain active during the daylight hours and protected them from possible outside predators, they were not hermetic and some losses occurred.
• The best behavior and development of prepupae occurred when the maximum environmental temperature reached more than 30° C.
• For better results, it would be important to design a facility that provides better protection against the environment including a constant temperature. The larvae and prepupae are most active in the dark so it is important to have warm night-time temperatures. This limits the natural growth season for black soldier flies in Idaho. The solution to this issue is to use a faster growing species of fly and/or grow the larvae in a controlled environment. The latter would add considerable cost to rearing the larvae.
• Even during summer, the wide range in temperature fluctuation between day and night could present challenges for growing black soldier larvae outside.

Objective 3) cost benefit analysis. The latter was not completed because we did not develop an adequate system to grow prepupae on dairy farms (see issues that we encountered).

Objective 4) plan and design a commercial pilot scale project. A proposal was submitted to the Idaho Dairymen’s Association in the fall of 2008 and declined. The dairy farmer on whose farm the flies were grown is interested in pursuing the project. As well, a house fly grower in Oregon is interested in submitting an SBIR with ISU and U of I as partners for developing an insect based fish feed. We are going to pursue a USDA SBIR proposal with this farmer (Skip Cockerum) in the fall of 2009.

Accomplishments/Milestones

We have completed most of our objectives. Data analysis and recommendations on the larval culture aspects of the project remain to be completed. Manuscripts, presentations, and a draft of an SBRI grant are also planned for the remaining 5 months of the grant.

Impacts and Contributions/Outcomes

Outreach and education: We had several local, national and international newspapers cover this project in 2008 (see Appendix A for the article in Associated Press and U of I’s press release covering this project). Also, three Western US agricultural radio stations have featured our project. One undergraduate student at ISU and at UI, and two undergraduate students at Texas A & M University have been trained how to raise black soldier fly larvae and conduct feed conversion studies.

Dissemination of results in 2009:

A demonstration project with live prepupae and larvae in a 3 ft circular container was presented at the following events:
• University of Idaho Twilight Tour-July 2008
• Gooding County State Fair-August 2008
• Thousand Spring Festival-September 2008
All three of these events are well attended by the farming community in Idaho.

The fish feed trial and sensory analysis will be presented at the Aquaculture America Conference and the Trout Farmers annual meeting in February 2009. Aquaculture American 09 is the annual meeting of the U.S. chapter of the World Aquaculture Society. More than 2000 fish farmers, researchers and aquaculture industry personnel attend to find the latest research on challenges to sustainable and profitable aquaculture. The study will be presented in both a technical section and in the Trout producers session to detail how successfully replacing 50% of the fishmeal component of trout diets can improve sustainability of trout production through reduced dependence on wild-harvested fishmeal while maintaining fillet product quality for human consumption. A manuscript to the Journal of the World Aquaculture Society will also be submitted by February 2009 highlighting the fish feed trial results. This journal is widely distributed in a number of countries to both the scientific community and the aquaculture industries.

A poster of the overall project will be presented at the 2009 Western Nutrient Management conference in Salt Lake City in March 2009 highlighting the manure management results and fish feed potential. The project will also be featured in Ag-Weekly in February 2009.

Collaborators: