Bioexposure assays to assess uptake and survival of viruses in mealworm (Tenebrio molitor) and black soldier fly (Hermetia illucens) larvae

Insects represent a sustainable source of food and feed. In order to increase the sustainability of insect production, new feed substrates should be explored including waste materials that contain animal by-products. However, the use of waste products does come with potential risks for transmission of pathogens. Experimental exposure studies of insects with selected pathogens can provide knowledge of some of these risks for future quantitative risk assessments. In this study, we have developed virus bioexposure assays to examine the uptake and survival of two different strains of porcine respiratory coronavirus (PRCV) in the larvae of two key insect species that are grown for the production of food and feed, namely the mealworm, Tenebrio molitor, and the black soldier fly, Hermetia illucens. T. molitor larvae were exposed to PRCV via oral uptake of virus suspensions while H. illucens larvae were exposed to PRCV via spiking of their feed. Using RT-qPCR assays, the amount of viral RNA extracted from individual larvae immediately after exposure varied from ~10 4.6 to 10 7.1 genome copies per insect. The PRCV RNA was detectable in the larvae of both T. molitor and H. illucens for up to 3 days post exposure but no longer. The assays applied to T. molitor and H. illucens for exposure to PRCV should be applicable for the exposure of further insect larvae to other viruses, and potentially also to other types of pathogens.