Microbial biopesticides are inhibited by honey bee royal jelly and in vitro larval diet

The interest in and use of biological materials in crop production is increasing globally at a rapid pace. In many cases, testing methods for conventional chemicals are applied to microbial-based biopesticides because specific microbial test methods are lacking. However, not all methods are easily transferred to microbial-based products. An evaluation was conducted to determine if OECD (Organization for Economic Co-operation and Development) Guidance Document No. 239 on honey bee larval toxicity could be adapted to microbial pesticides. In our study, five microbes, including B. pumilus, B. thuringiensis, B. velezensis, Paenibacillus larvae, and Ascophaera apis were grown on agar media and spotted with either honey bee in vitro larval diet or royal jelly. We observed that the honey bee larval bee diet and royal jelly did not inhibit the fungal honey bee pathogen Ascophaera apis, yet inhibited the growth of bacteria, including a known honey bee larval pathogen. This finding may make the test unreliable for certain biopesticides. The OECD is considering biopesticide-specific testing guidelines, and the EPA has indicated it to update itsbiopesticide bee test guidelines. However, additional research is needed to determine which options may be feasible and provide the best improvements. © The Author(s) 2024.