Using Soldier Flies as a Manure Management Tool for Volume Reduction, House Fly Control and Feedstuff Production (AS93-09)

Using Soldier Flies as a Manure Management Tool for Volume Reduction, House Fly Control and Feedstuff Production (AS93-09)

Summary

Objectives
The overall objective is to develop a system to manage a native nonpest soldier fly larvae (SFL) to; (1) reduce manure accumulations where livestock is housed, (2) eliminate house flies and (3) produce tonnage of high quality feedstuff. Currently this system is being developed for caged layer houses and specific objectives are:
1.) Determine depth of manure basin necessary to allow SFL to utilize manure accumulated during the previous winter.
2.) Characterize plant nutrients in layer manure with and without SFL.
3.) Evaluate manure volume reduction, esp. of winter accumulation.
4.) Evaluate SFL feedstuff production, quality and utilization.
5.) Determine feasibility of using this system in high-rise layer houses.
The black soldier fly (Hermetia illucens) occurs worldwide in the tropics and temperate regions. The larvae of this large, wasp-like fly occur in very dense populations on various organic wastes and excludes other flies. We are developing a manure management system for caged layers using soldier fly larvae (SFL). In our system, wild populations of SFL are managed in concrete basins under the hens (could be hogs or cattle) to:
1.) Eliminate house fly breeding.
2.) Eliminate half of the manure through incorporation into larval biomass.
3.) Produce large quantities of high quality feedstuff (42 percent protein, 35 percent fat) through self-harvest of prepupae (ca. 65 tons/100,000 layers annually). SFL convert manure to meat about as well as hogs convert their feed.
This system will greatly reduce manure handling and pollution potential and increase feedstuff production. This contribution of high quality feedstuff could be a huge benefit to the livestock industry, especially if world menhaden (fish meal) stocks continue to decline. Twenty-three thousand tons of dried larval feedstuff with a minimal value of $7 million could be produced in the Georgia layer industry each year. If adapted to broilers and swine, over a larger geographic area this would be multiplied many times. Environmental benefits may be more valuable than direct economic returns.
Utilization of the larval feedstuff has been extensively studied. It has been successfully incorporated into the diets of poultry, fish and swine with hogs actually preferring a larvae based diet over a soybean diet. One of the most remarkable things about this system is that the larvae self-collect themselves. They do this as they are leaving the manure basin to transform into the adult. At this stage they are at their maximum size, with a large store of fat. This fat is to sustain them to adulthood, but is a valuable feedstuff. This stage does not feed. Considering their diet, this is a definite plus.

Approach
The 24-by-60-foot experimental caged layer house was completed and 1700 layers were installed in September 1994. About 41,000 SFL were released into the outer two pits (there are four pits) where they were managed. The inner two pits were sprayed with Larvadex® to eliminate any larval activity. Soldier fly activity had almost stopped when hens were installed in late September. The larvae that were released overwintered in the general area, emerged as adults in April and laid their eggs.
One main objective was to determine if SFL could digest the stockpiled, winter-accumulated manure. If this was successful it would have almost doubled the benefits of manure reduction and feedstuff production. In previous studies SFL had been successfully used to manage manure as it was produced in the warmer months of April to October.

Results
Unfortunately the deep, dry base of older manure caused two problems in 1995; failure of prepupae to exit the pit to self-harvest and a darkling beetle outbreak. Also, there was a house fly outbreak in the fall just after hens were introduced. None of these problems had occurred in previous studies with a spring manure clean-out and an established SFL population in-place through the fall and winter.
The commercial scale manure basin was effective in harvesting the prepupae that did attempt to exit, and manure clean-out was routine with a small Kobuto tractor with front-end loader.
In 1996, returning wild female soldier flies established a robust larval population soon after hens were installed on April 29. An ovipositing female survey at this house (one time count in the early afternoon) indicated an average of 52 present and ovipositing on each of 29 counts from May 7 to August 20. Assuming a residence time of 15 minutes (true residence time unknown) and an active oviposition period of five hours, then 1040 females would oviposit daily.
Given an average mass size of 998 eggs, then over a million eggs would be laid daily to digest the manure of the 1900 hens. Given a residence time of two months per larvae, a population of about 60 million would develop.
All of this oviposition is from a wild population residing around the manure management facility. House flies were controlled, and no lesser mealworms developed in pits where soldier fly larvae were allowed to establish.
Analysis indicated that plant nutrient amounts were about the same in manure digested by soldier fly larvae as in undigested manure. The four-foot-high, 40-degree ramp for prepupae self-harvest did not allow the same rate of collection as previous designs. This flaw was not evident in the low collections of 1995.
Three problems became evident in 1996: 1) height was excessive two and a half feet would be sufficient, 2) 40- degree angle was marginal. It should be less, and 3) rough texture on ramp was a mistake. It should be smooth so climbing prepupae do not turn over and roll back down the ramp.
In 1997, new collection ramps were installed that are lower and smoother to optimize prepupal collections slopes were built to a height of 29" at a 35 degree angle. No pits were treated with larvicide since these pits seemed to be acting as an egg sink; attracting ovipositing females, but producing no larvae.
In 1997 returning wild female soldier flies again established a strong larval population. Lesser mealworms were not a problem as they had been last year. Timing the annual clean-out in spring would maintain control of these pest beetles. Larval collections with thismodification were good, and construction will be more economical.

Bull frog experiment
Bull frogs were reared on a diet of self-collected live soldier fly prepupae and catfish pellets in a system patterned after commercial frog production in Latin America. In the Latin American system, house flies are cultured at some expense on dairy by-products. By using soldier fly larvae, our live feed is a by-product of manure management. This is our second year raising frogs from tadpole to adult on this diet. Dr. Larry Newton has been the lead in this research. The above chart is a data summary comparing our rearing to that of a Mexican frog-culturist:
Given our low feeding rate, general lack of experience in this area, and use of a wild strain of frog, these results seem encouraging. Use of a strain of frog adapted to captivity would probably enhance growth greatly. Also, we only fed three days a week.

Greenhouse experiment
Soldier flies were colonized briefly in a greenhouse. Two thousand prepupae were placed on August 30 and the first emerged adult was seen September 9. First chasing (males after females) and mating was seen on September 13. On September 15 a female was seen in the media bucket with ovipositor extended, but no eggs were found. First eggs were deposited September 16 (these were fertile). Twenty-five egg masses were collected on September 17; also much chasing and mating on September 17. Forty-seven egg masses were collected on September 19. Adults were never seen to feed, but did go to cool-cells (wet cooling pads) to get water. Pig weed that had volunteered on the greenhouse floor was a favorite resting site. Maximum numbers of adults ever present was estimated to be 75 on Sept. 16. This dwindled to four on October 1. Soldier flies exhibit a very extended and variable time to emerge and a few adults continued to appear into February. Mass culturing for initiating new populations for waste management seems feasible.