Efficacy and persistence of entomopathogenic nematodes for biological control of small hive beetle under glasshouse conditions

Abstract The small hive beetle (SHB) poses a serious threat to honey bees, impacting colony health, honey production and pollination services. Entomopathogenic nematodes (EPNs) may provide effective and lasting SHB biocontrol. We assessed the efficacy in causing mortality and persistence of nine Australian isolates of four EPN species after a single application against three cohorts of SHB wandering larvae sequentially released in natural (not autoclaved) and autoclaved (sterile) soil under glasshouse conditions across 161 days. In natural soil, Heterorhabditis indica Hi.HRN was superior, maintaining high persistence with total (pre- and post-emergence) SHB mortality decreasing from 84.4% (cohort 1) to 64.9% (cohort 3) by day 161. In contrast, the least effective isolate, Steinernema feltiae Sf.BR1 achieved 37.3% total SHB mortality (cohort 1), which declined to 10.7% (cohort 3). In autoclaved soil, Hi.HRN was again the most effective, with total mortality declining from 94.3% (cohort 1) to 72.1% (cohort 3). Conversely, the least effective isolate Sf.BR1 consistently displayed low total mortality, decreasing from 16.2% (cohort 1) to 12.4% (cohort 3). Recovery of infective juveniles (IJs) from the soil after 161 days was three- to 51-fold higher in natural soil than autoclaved soil, indicating that soil moisture and interactions with other soil organisms play a critical role in enhancing EPN survival. Overall, treatment with isolates of H. indica (Hi.HRN and Hi.LMBT) and H. bacteriophora (Hb.EG) were highly effective, retaining over half of their initial high efficacy in causing SHB mortality even after five months, highlighting their potential for sustained SHB management under field conditions.