Is Metarhizium brunneum ovicidal against grey field slug (Deroceras reticulatum) eggs?

Slugs cause crop losses worth over £100 million annually. The grey field slug (Deroceras reticulatum) ranks as the most economically important slug species, especially of winter wheat and oilseed rape. Withdrawal of metaldehyde based molluscicides due to the risks they posed to human and animal health has prompted a search for more benign, sustainable products. The entomopathogenic fungus, Metarhizium brunneum, is known to possess ovicidal properties for a range of invertebrate species. This study evaluated both aqueous and oil formulations of M. brunneum strains ARSEF 4556 and V275 against freshly laid eggs of D. reticulatum. Conidia of M. brunneum suspended in aqueous with Tween solution (1 × 106, 1 × 107, and 1 × 108 conidia/mL respectively) had no significant negative impact on slug eggs when compared to the control group. However, oil-formulated conidia (1 × 108 conidia/mL) caused significant mortality and was similar to mortality caused by the oil only control. This suggests that the oil carrier itself caused the egg mortality, indicating that M. brunneum is not an effective bio-ovicide. Interestingly, M. brunneum did grow and sporulate on the dead slug eggs. Future studies will investigate the effects of M. brunneum on the juvenile stages of slugs to better understand their potential role in integrated pest management.