Entomopathogenic nematodes (EPNs) have received much attention as alternative biological-control agents to conventional synthetic agrochemicals. Since, EPNs are considered natural enemies, registration is often based on limited or no data. For the first time, we show that exposure to a commercial EPN product can significantly reduce honeybee survival and nematodes can successfully replicate in infected adult bees. Newly emerged honeybees (Apis mellifera) and larvae of the greater wax moth (Galleria mellonella) were exposed to dry and wet foliage residues at a low (0.25 Mio/m2) and medium (0.5 Mio/m2) field-realistic concentration of Steinernema carpocapsae. Mortality was assessed over 96 h and nematode reproduction was evaluated in all dead individuals. EPN exposure significantly reduced wax moth larvae survival across both treatments (p's < 0.001), resulting in an increased mortality rate of 80%. Honeybee survival was also significantly reduced (p's < 0.001). However, the data revealed a dose-dependent effect wherein the medium concentration led to a significantly higher mortality rate (55%) than the lower dose (43%) when compared to the non-exposed control. Nematode reproduction was significantly higher in wax moths than in honeybees (p < 0.001), yet no significant difference was observed between the low and medium treatments for either species (p>0.56). Mean nematode reproduction per individual wax moth and bee was 126'695 and 4'370, respectively; representing a 29-fold increase in wax moths. The data show that EPN exposure can adversely affect honeybees. Due to the vast lack of data regarding potential adverse effects of EPNs on non-target pollinating insects, our results underline the urgent need to act cautiously when considering foliar application of EPNs on crops. Further research is required to adequately address the potential risk of EPNs to bees and other non-target species regarding foliar and soil application.
