Eating insects – a tasty solution to today's global problems

The aim of this project was to develop a new protein- and mineral-rich Swedish food based on crickets. The project covered the entire value chain, i.e., a feed production system that included ecosystem services, cricket farming, and the creation of safe, tasty Swedish dishes. This unique holistic project thus began with the biodiversity of Swedish nature and ended at the dinner table. 

Effects on biodiversity

One of our main hypotheses was that flowering plants, especially red clover, can be used as an ingredient in cricket feed. It has been suggested that red clover as a crop can support biodiversity, especially pollinators, when grown on arable land. However, to date, few studies have been conducted on the effects of flowering crops on bumblebee abundance and diversity during and after crop flowering. During fieldwork for the project, we observed that bumblebee worker abundance was higher in red clover than in flower-rich field margins in the same landscape. Red clover had positive effects on bumblebee species richness and diversity after crop flowering and was also positively correlated with the occurrence of a certain less common bumblebee species. These results led us to conclude that red clover cultivation has the potential to benefit less common bumblebee species in Swedish agroecosystems.

Effects of diets containing flowering plants

Other results from the project showed that red clover can be included in the diet of crickets without any problems, but cannot be used as the sole ingredient. We observed no difference in weight or survival between crickets fed early or late harvested red clover, suggesting that the crop can be harvested for feed purposes after flowering, which also allows it to support wild pollinators. The feed preservation method had no effect on weight and survival, or on how efficiently the feed was used by the cockroaches (weight gain per unit of feed consumed). In free-choice tests, we found that cockroaches with access to red clover (in addition to a cereal-based control feed) matured earlier than cockroaches that only had access to the control feed. The addition of red clover thus appeared to promote the maturation of the crickets, which may be an advantage in commercial breeding. Overall, it seems interesting to include red clover in the diet of commercially bred crickets, both from a production perspective and from an ecological perspective, as the flowering crop will provide food for bumblebees and other pollinators. Other flowering plants that showed some potential as cricket feed were alfalfa and white nettle. Grasshoppers fed white nettle showed good growth during the early stages of development. This plant attracts pollinators but is not commercially grown as a field crop, making it a suitable subject for future cultivation studies.

In our studies, the drinking water consumption of crickets was approximately half that reported for pigs and poultry. However, crickets require a certain level of humidity (and temperature) for optimal growth and survival (>50% relative humidity and approximately 30°C), which means that the rearing system may require more water than just drinking water during dry conditions. There were some differences in the nutritional content of the crickets depending on the diet they were fed. Compared to crickets fed a control diet based on grain, crickets fed diets containing red clover and alfalfa had lower total fat content, lower content of monounsaturated fatty acids, and higher content of polyunsaturated fatty acids. This pattern is similar to that observed in meat from cattle fed fodder or pasture instead of grain. The copper content in the crickets was highest with the red clover diet and the magnesium and manganese content was lowest with the alfalfa diet, but there were no differences in zinc and iron content between the diets. There were also no differences in the total amino acid content of the crickets between the diets. Compared to values reported for eggs, beef, and green peas (Swedish Food Agency), the lysine content in crickets was three times higher than in green peas, similar to eggs, and about half that of beef. For methionine, the content was two to three times higher than in green peas, slightly lower than in eggs, and half that of beef.The iron content was higher than in eggs and green peas and similar or slightly lower than in beef. These results confirm that crickets contain important nutrients and that diet may have some influence on the fat and trace element content of crickets. We also studied the impact of diet on cricket behavior using three diets with 0, 10, or 20% feed replacing a similar proportion of grain (wheat flour). The feed appears to affect cricket behavior, and the addition of feed can potentially reduce behaviors related to anxiety and high energy consumption. Using feed instead of grain in house cricket feed would also promote biodiversity in the landscape. Overall, our results suggest that using feed in the diet may be beneficial for production and insect welfare, but further studies are needed to verify these observations.

Food safety

We have established a risk profile and identified knowledge gaps based on a review of previous publications. The review showed that crickets as food may contain higher microbial levels than other food products; for example, raw crickets appear to contain higher microbial levels than food from poultry, pigs, or cattle. Salmonella spp. and Escherichia coli have sometimes been found in edible insects, possibly because the whole insect is consumed, including the contents of the intestine. Therefore, specific hygiene and safety criteria must be applied before they are consumed by humans. Heat treatment, such as blanching, boiling, or frying, can reduce microbial loads. A mandatory heat treatment process for crickets or products derived from crickets should be implemented before such products are placed on the market. Cooking before consumption may also be recommended to ensure that microbial loads meet hygiene and food safety standards. However, such treatments may not be sufficient to kill spores from certain bacteria (Bacillus spp. and Clostridium spp.) and therefore new processes (e.g., high-pressure treatment) and preservation treatments, such as the addition of nitrifying salts, drying, or acidification treatment, should be considered to ensure longer shelf life. Heavy metals are potential chemical risks when crickets are exposed to them during rearing, and cadmium accumulation in particular has been identified as a problem.

Cadmium can enter the farming system via feed, although this risk is likely to be lower in Sweden than in other countries, as cadmium contamination in fertilizers is prohibited under Swedish law. Crickets can also trigger allergic reactions in consumers who are sensitive to shrimp, crab, and lobster. For safety reasons, crickets and food products derived from crickets should be labeled to raise awareness of this risk among sensitive consumers. In summary, our risk profiling identified several significant problems (high risk) in the production of cricket-based foods: (1) high total aerobic bacteria count, (2) survival of spore-forming bacteria after heat treatment, (3) allergenic properties, and (4) bioaccumulation of heavy metals (e.g., cadmium). Other hazards, such as parasites, fungi, viruses, prions, antimicrobial resistance, and toxins, were classified as low risk. Based on the literature review, we identified several knowledge and data gaps in food safety, e.g., regarding fungal and mycotoxin production and chemical compounds such as heavy metals or dioxins.

The identified data gaps could be divided into four main categories: (1) rearing conditions for the insects, (2) the actual effect of heat treatment prior to consumption, (3) fungal communities and mycotoxin-producing fungi in farmed crickets, and (4) heavy metals that have not been fully evaluated and other chemical risks arising during processing. In addition, we found very little information on the traceability of marketed insects, particularly with regard to the rearing environment, veterinary products used, and transport and storage conditions. 

Bacterial and viral microbiota in rearing systems

We investigated microbial communities (bacteria, mold, yeast) in crickets fed different diets in a controlled environment. We observed high levels of aerobic bacteria, but all samples tested negative for Salmonella, Listeria monocytogenes, Bacillus cereus, and Clostridium perfringens. Mold was detected, and Aspergillus flavus, a fungus that can produce mycotoxins, was detected in crickets fed one of the red clover diets. The high microbial load detected in the crickets indicated a high risk of rapid spoilage, but the diet used did not appear to have a significant impact on the total amount of aerobic bacteria. Given the high microbial load in the crickets, we recommend, in order to prevent any food safety issues, that the crickets be heat-treated at harvest, immediately after the rearing phase is completed, to extend their shelf life. 

Overall, our results indicate that there is a need to monitor rearing conditions, including possible fungi in the feed, to prevent mold growth and mycotoxin production in edible crickets. More work is also needed to establish possible reference values for bacterial quality. This will be an important step in the development of parameters to ensure consumer safety. We also investigated viruses in crickets fed different diets. The results showed that only a limited number of viruses were present, regardless of diet. This may be because the crickets had not been exposed to a virus-rich environment, which is a good sign from a food safety perspective. Further analyses of the viral flora under industrial cricket rearing conditions need to be carried out. 

Dishes and sensory properties of crickets

Chef Paul Svensson and his team created three dishes, pasta with pesto and two desserts, using crickets fed the grain-based control diet (see blog). Another team of chefs was asked to evaluate the taste of crickets fed different diets. In this evaluation, the chefs perceived a difference in taste between crickets fed different diets. These differences were observed for flavors such as “roasted,” “milk,” and “buttery.” These observations show that it may be important to evaluate sensory properties before introducing new feed sources into cricket diets in the future. 

Denso virus

Another important part of our project was to investigate the prevalence of the cricket densovirus in commercial and wild crickets in Sweden. This virus has been found on commercial farms in Europe and the US and causes high mortality, with devastating effects on production. If Swedish crickets proved to be free of the virus, there could be commercial value in creating a virus-free strain for food production. During 2017–2018, we collected samples from commercial retailers (who sell to pet owners) and from wild populations in Sweden. No individuals from the wild populations carried the cricket densovirus, but insects obtained from retailers did carry this virus. Using wild individuals that were found to be free of the virus, we created a virus-free breeding strain for studies at the university. In another part of the study, we showed that fecal material from crickets is a suitable substrate for analysis when assessing whether a cricket population is infected with densovirus. We also developed a method for detecting the virus that is more sensitive than previously published protocols. This method is now commercially available, as are virus-free breeding crickets. 

Conclusion

The overall positive conclusions from this project are that farmed crickets are a protein- and mineral-rich food source and that cricket production can contribute to ecosystem services through the inclusion of flowering plants in the diet. There may be a high risk of food products based on crickets spoiling quickly, but measures can be taken to prevent this. Cricket farmers should be informed that the deadly densovirus is present in Swedish commercial stocks and that there is a test to detect this virus.