Testing low-risk bioactive compounds on Halyomorpha halys: an improved pipeline of analyses to investigate their effects on the bacterial endosymbiont Candidatus Pantoea carbekii.

BACKGROUND: The brown marmorated stink bug Halyomorpha halys has become an invasive insect pest of many crops. A promising control strategy to manage the proliferation of H. halys is based on the suppression of its obligate and vertically transmitted uncultivated symbiotic bacterium Candidatus Pantoea carbekii through surface-sterilization of H. halys eggs. Indeed, the application of antimicrobial formulations on the eggs of H. halys could cause mortality of endosymbiont and consequently of newly emerged nymphs. In this study, a microbial live/dead assay was applied directly on H. halys eggs to evaluate Ca. P. carbekii loss of viability after treatments with seven commercial formulations including fungicides (copper hydroxide, sulphur, sweet orange essential oil) and plant biostimulants (flavonoids and chestnut tannin extract) compared with two disinfectants for civil and industrial use (sodium hypochlorite/hydrated sodium/tetraborate decahydrate and peracetic acid/hydrogen peroxide). Impact of mode of application was also evaluated, as surface treatment of egg masses was performed through spraying and dipping in laboratory conditions. Antimicrobial activity data were finally complemented with observations of egg hatching and vitality of the nymphs.

RESULTS: The optimization of live/dead staining is useful for evaluating Ca. P. carbekii mortality directly on eggs, providing a rapid and reliable culture-independent approach. Sodium hypochlorite, copper, sulphur, tannins and sweet orange essential oil showed an antimicrobial effect against Ca. P. carbekii and a H. halys egg hatching reduction and nymph's vitality.

CONCLUSIONS: The antimicrobial and insecticidal effects of these commercial products should be further studied to assess their in-field efficiency as well as the impact of these substances on non-target organisms. The approach followed in this study could be considered a robust pipeline of analyses to evaluate the effectiveness of antimicrobial eco-friendly compounds in symbiotic control of H. halys. © 2024 Society of Chemical Industry.