A small amount of black soldier fly larvae can increase the resistance of the immune system of broiler chickens and increase their survival in outbreaks of avian typhoid.
The feed with the addition of black soldier fly larvae (BSFL)  is becoming increasingly popular as a protein-rich substitute for fish meal and soy in animal feed. In the feed of broiler chickens, the larvae can replace substantial amounts of soybeans without any harmful effects on the health of the birds. In addition, the feed with the addition of larvae significantly affects the growth of broilers and, thus, is important for private farmers and commercial agricultural enterprises.
Study of immune responses
In a recent study by Lee et al. (2018)  scientists have studied the immune response of broiler chickens to Salmonella enterica serovar Gallinarum (S. Gallinarum) when the black soldier fly larvae was added to the feed. S. Gallinarum is a gram-negative bacterium that causes typhoid fever, which often leads to anorexia, diarrhea, dehydration, as well as anemia, enlarged liver and spleen, bleeding in the intestines and high mortality (Shivaprasad, 2000; Lee et al., 2007). In general, typhoid fever is a serious problem for poultry in Asian countries such as Korea and India (Barbour et al., 2015). The inclusion of BSFL flour even in relatively small amounts in the diet led to increased immune responses in broiler chickens, as well as reduced mortality and reduced pathogens when chickens were infected with S. Gallinarum. This, in addition, was accompanied by an increase in body weight. Although nowadays typhoid fever is not found in most European countries and North America, the results of this study show general preventive properties and stimulation of a nonspecific immune response in broiler chickens when black soldier fly larvae flour is included in their diet. This, in turn, can have a beneficial effect on the performance of the poultry industry as a whole.
The effect of the black soldier fly larvae added feed on the resistance of the immune system
In the course of the experiment, broilers received feed from the first day with the addition of 1%, 2%, or 3% (of the total mass) of the black soldier fly larvae. On the 20th day, spleens were removed from the chickens to examine the ratio of CD3 + and CD4 + T lymphocyte subpopulations . Both cell types are highly effective markers for the activation of the immune system (Fair et al., 2008; Abdukalykova et al., 2008). The number of CD3 + and CD4 + cells was significantly higher in birds fed with BSFL added feed, compared with the control group. The number also changed depending on the dose of added flour, it increased with the inclusion of 2% of the larvae (P <0,05) and 3% of the larvae (p <0.013). These results indicate that the addition of flour has a positive effect on the immunity of broiler chickens.
Increased lysozyme activity
If we talk about the activity of lysozyme, it was also higher in broiler chickens fed with the black soldier fly larvae added feed of 2% (P <0.05) and 3% (P <0.01). Lysozyme is an enzyme that destroys the walls of bacterial cells and is associated with increased efficiency of phagocytes, such as macrophages  and granulocytes . In connection with such results, it can be assumed that BSFL flour enhances the destructive action of phagocytes in broiler chickens.
The effect of the black soldier fly larvae added feed on the progress of avian typhoid
In the next study, aimed at determining the effect of the black soldier fly larvae added feed on immunomodulation, the scientists infected healthy 18 days old chickens with S. Gallinarum (oral infection at a concentration of 5 × 1010 CFU, which is much higher than the normal concentration found in natural conditions). As a result, chickens fed with the addition of larvae lived 2 to 3 days longer than the rest of them. Even more importantly, even on the 15th day of the studies, the survival rate of the chickens fed with the BSFL added feed was also significantly higher than the survival rate in the control group. These results correlated with the flour addition dose: the group with no additive — 50% survival rate, with 1 percent BSFL inclusion — 67% and with 2 percent — 75%. The addition of 3% of the fly larvae led to an increase of this indicator to 85%. At the same time, previous studies of birds infected with S. Gallinarum showed almost 100 percent mortality rates, and birds aged 2 to 3 weeks turned out to be particularly susceptible to the disease (CFSPH, 2009; Shivaprasad, 2000; Barrow and Neto, 2011). Thus, the addition of even small volumes of black lion larvae to feed leads to a significant increase in the percentage of survival of broiler chickens artificially infected with S. Gallinarum.
Destruction of pathogenic organisms
16 days after infection, the number of viable S. Gallinarum cells in the liver, spleen, Bursa fabricii  and caecum of the infected broiler chickens was significantly less in the groups fed with 2% and 3% larvae added feed compared with birds in the control group (in the liver, spleen and caecum with the addition of 2% (P <0.05) and 3% (p <0.01) and in the Bursa fabricii at 3% of the larvae in the feed (p <0.01)). These results show that the larvae of the black soldier fly indirectly increase the resistance against S. Gallinarum.
Increased growth rate of broilers
In previous studies, it has been shown that immune stimulants accelerate the growth of broiler chickens due to the positive effects on the health of birds in general (Landy et al., 2011; Faluyi et al., 2015). This hypothesis was confirmed in a recent study by Lee et al. (2018). Broilers fed with the addition of black soldier fly larvae gained weight faster and reached 1.3 kilograms two days earlier than birds with a standard diet (30 days and 32 days, respectively).
Thus, the results of immunological and infectious studies show that black soldier fly larvae act as non-specific stimulants of the immune system and generally increase the resistance of chickens against bacterial pathogens. It can be argued that small amounts of larvae can be added to poultry feed in commercial poultry farming for preventive purposes and to increase the level of survival of the population. In addition, the black soldier fly larvae retain their properties much longer during storage in comparison with antibiotics. However, the components in the larvae, which are responsible for the observed effect, are still unknown and require additional research.
 BSFL – Black soldier fly larvae.
 LEE J. et al. Black soldier fly (Hermetia illucens) larvae enhances immune activities and increases survivability of broiler chicks against experimental infection of Salmonella Gallinarum //Journal of Veterinary Medical Science. – 2018. – T. 80. – №. 5. – p. 736-740.
 The study of the number of subpopulations of T-lymphocytes CD3 + and CD4 + – a standard analysis to assess cellular immunity.
 P-values show the error of deviation from the null hypothesis, i.e. how accurate is the assumption that with increasing concentration of flour from the larvae in the feed, immune resistance will increase.
 Scavenger cells are white blood cells capable of actively capturing and digesting bacteria, debris of dead cells and other foreign or toxin for the body substances.
 Granulocytes are white blood cells that act against bacteria, fungi and parasites.
 CFU – colony forming units.
 The Bursa fabricii is an organ in birds that is responsible for the development of B-lymphocytes.