Results

The manufacturing costs of insect meal production depend to a large extent on the cost of raw materials. As an approach to optimize the costs of the production process, low-cost raw material sources based on residues have been investigated as a substrate for insect production. This included the investigation of substrate suitability, characterization of material properties and concept development for raw material handling.

Procedure and methodology

Basics and experimental setup

The entire process of hermetia production can be subdivided into two production stages, whereby the first stage of insect production focuses on insect recovery and the second stage of larval production involves the rearing of young larvae. Figure 1 shows a schematic representation of the hermetia production process.

 

During insect production, the eggs of the hermetia fly are collected, which are used in larval production for breeding insect larvae and pupae. Some of the larvae develop into hermetia pupae, which grow into sexually mature hermetia flies during insect production and lay new hermetia eggs. The remaining hermetic larvae, which are not used for insect production, are removed from the larval production before pupation and processed into hermetic meal. The use of cost-effective feed materials is of particular economic importance in the production stage of larval production, as large quantities of substrate are required for the rearing of young larvae. On a laboratory scale, different feed alternatives have been investigated in detail, especially in the field of larval production.

 

Hermetia Baruth GmbH provided young larvae for laboratory-scale feeding trials. The young larvae were delivered to the DBFZ laboratory at an average age of 9-12 days after egg deposition. At this time the young larvae had an average weight of approx. 2.4mg and an average size of 2 mm. The growth of the young larvae was tested on different substrates in parallel feeding experiments on a scale of approx. 250ml. For this purpose, the young larvae and the test substrate were each weighed in as a triple batch in different mixing ratios and tempered over the entire test period (see Figure 3). The larval growth and the larval end weight were documented over a trial period of 13 - 17 days. The experiments were performed until the weight of the larvae remained constant. After reaching the abort criterion, the sample preparations were sieved and residual materials and larvae were examined individually. Material analyses were carried out on the adult larvae and the input and residual materials. The growth rate of the larvae could be calculated and the overall efficiency of the feed conversion of the investigated substrates could be evaluated.

Substrates investigated

The following raw materials have so far been investigated as potential feed for hermetic larval breeding:

Residual and waste materials

  • dry chicken excrement
  • Fermentation residue from agricultural biogas plant
  • Fermentation residue from industrial biogas plant
  • Aquatic plant Elodea Nutallii
  • Aquatic plant silage Elodea Nutallii
  • Aquatic plant Myophyllum
  • Aquatic plant Lemna Minor
  • Aquatic plant Nymphaea alba
  • Corn silage feed residues from dairy cow husbandry
  • Feed remains from insect breeding

Residues or by-products with livestock feed quality

  • brewer's grains
  • Dried pressed stillage (DDGS) from bioethanol production
  • Grain stillage liquid silage
  • coffee residues

The substrate selection can be divided into two groups. The residues of cereal stillage, brewer's grains and coffee residues belong to the feed materials that are legally harmless for animal feed and may be used for the economic production of Hermetia according to current legal requirements. According to EU Regulation 1069/2009 Animal by-products (Article 3 point 6), the black soldier fly is defined as a farm animal. Thus, in Europe at present only animal feeds may be used as input materials for hermetia production. Regulation 999/2001 BSE/TSE states that no processed animal protein (PAP) may be fed to farm animals. In 2001, only the exception fishmeal was allowed. Since 1 July 2017, protein meal from seven insect species may be fed to fish in aquaculture (farm animals). The regulation is an annex to 999/2001 and has the number 2017/893. The issue of insects is part of other relevant regulations such as Regulation 767/2009 - Marketing and use of feed and Regulation 68/2013 - Catalogue of feed materials.

Investigated process conditions

In parallel feeding experiments with different substrate samples, the following influencing factors on the growth behaviour of hermetic larvae were investigated in more detail:

  • Process temperature
  • Temperature of the substrate at the beginning of the test
  • Feed concentration and water content of the substrate material
  • Drying behaviour of the substrate during the feeding experiment
[Translate to Englisch:] Versuchsmaterialien der Fütterungsversuche im Labormaßstab

Figure 3  Experimental materials of the feeding experiments on a laboratory scale

Experimental methodology

Methodology of feeding trials

The feeding experiments were carried out with three different feeding methods (160, 240 and 320 mgoTS/ larvae), each as a triple approach (see Table 1). The test temperature was 30°C over the entire test period. The sample containers used were lockable plastic boxes with air holes.

Working steps

  • Determination of the single larval weight - Repeated measurement of the weight of 20 single larvae and subsequent calculation of the single larval weight Determination of the single larval weight by averaging.
  • Calculation of the required larval mass of each feed concentration.
  • Labelling and weighing of the plastic boxes with lid without filling.
  • Addition of the substrate mixture to the young larvae.
  • Weigh the cup weights with lid after filling.
  • Seal the cups and storage at at 30°C temperature.
  • After 3, 6, 10 and 12 days of testing, 10 young larvae are to be removed. Clean carefully - rinse briefly for 10 minutes, then dry with cellulose cloths and calculate and note the individual weight of the larvae. Then return the larvae to the batch.
  • Finish the test after 12 days. The beaker weights are noted again. The adult larvae are then screened, washed and left to dry on cellulose for 10 minutes, after which the total weight of the larvae is determined. The larvae are separated by sieving (mesh size 5 mm). Food remains must be collected for subsequent analyses (TS, oTS, etc.).
  • The TS and oTS values of the lavas and feed residues are then determined and recorded.

Results and discussion

In the following section the achieved results of the feeding experiments are described in more detail and different substrate evaluation approaches are presented.

Food Conversion Ratio (FCR)

The evaluation of feeding systems in livestock farming and aquaculture is often based on the Food Conversion Ratio (FCR). The value provides information on the efficiency of feed conversion and indicates how many kilograms of dry matter of the feed material are required to build up one kilogram of livestock. A low value indicates good feed conversion, while high values indicate poor feed conversion. Table 1 shows the FCR values of different livestock. The results of our studies are consistent with those of other Hermetia studies. The best feed conversion could be achieved with cereal grind. Good results were also achieved with brewer's grains, maize silage and insect feed. The feed conversion was worse with the samples agricultural fermentation residue, Elodea water plants, dry chicken faeces and Schlempegärrest. Figure 4 shows the calculated FCR determined for different substrates at three tested feeds (80, 160 and 240 mg/l oTS substrate per young larvae).

 

livestock speciesFCR g TS Input/g FM OutputLining
Beef cattle4.5–7.5 (> 6 typical)Feed mix
Pig3.8–4.5Feed mix
Chicken1.6–1.9Feed mix
Sheep

4.0–6.0

40.0

Feed mix

Straw

Fish (Aqua culture)0.75-2dry feed pellets
Hermetia2.0–3.2Oil palm kernel flour
 0.8–2.1grain stillage

Typical FCR values of different livestock species

However, the approach of evaluating feeding systems using the FCR also has disadvantages. For example, the ash content of the feed and the water content of the product are not taken into account. More precise is the consideration of the turnover of the organic dry matter. The water and ash content in the product and feed have no influence on this consideration. Only the organic turnover is evaluated. The best oTS yields of approx. 25% were achieved with stillage. The oTS yields of the samples corn silage, brewer's grains and insect caused damage were between 8 and 12%. An oTS yield of approx. 2 to 7% was achieved with the residues dry chicken faeces, fermentation residue, aquatic plants and plum fermentation residue. (See Figure 5)

Larval yield

The feeding trials have shown that between 18 and 120g adult larvae can be obtained from one gram of young larvae after approx. 12 days of testing. However, depending on the substrate composition and the feeding, the yields vary considerably (see Figure 6).

 

Interim conclusion

The results of the feeding trials have shown that stillage, brewer's grains, maize silage feed residues are very well accepted as feed material by the hermetic larvae (see tables 1 and 2). The other substrates tested achieved comparatively lower product yields. Larval growth was largely completed after about 10-12 days of feeding. After a short adaptation time to the substrate medium of approx. 3 days, rapid larval growth began. The mass of the individual larvae increased during the test period from approx. 2.4mg initial weight to a maximum of 280mg final weight.

Between 18 and 129 g of adult larvae could be obtained from one gram of the young larvae used. The effect of the feed concentration on larval growth was clearly shown. Lower feed intake led to a weaker growth of the larvae. Of the three feeds 80, 160 and 240mg oTS / larvae tested, the highest feed concentration led to the strongest weight increase of the young larvae used.

The weight of an adult hermetic larva was about 280mg FM at the end of the experiment, whereas the oTS weight of a single larva was about 80mg after deduction of water and ash. In the feeding experiments with a substrate concentration of 240mg oTS, between 3 and 28% of the substrate oTS was converted into larvae oTS. However, the most effective feed conversion could be measured in the approaches with a low feed concentration. With a low feed supply, the feed material used was apparently converted more completely. High feed concentrations, on the other hand, seem to lead to a worse turnover. The results presented are from laboratory experiments. The transferability of the results to the practical scale must be investigated in greater depth.

 

Test conditions: Temperature 30°C / feeding 240mg oTS/ larva / feeding time approx. 12 days
FM = Fresh mass - original substrate
oTS = organic dry matter after deduction of water and ash from fresh mass

Outlook

In addition to the results of the feeding experiments, the substrate costs of the tested feed materials have a significant influence on the substrate selection. The substrate costs are researched in the course of the project and transferred to the substance database. On the basis of the feeding experiments, cereal stillage, brewer's grains and feed residues appear to be suitable substrates for the hermetia method. Further feeding trials are planned with residues from biodiesel production and other agricultural waste materials.