Pest Control or Pollinator Peril? Evaluating Entomopathogenic Nematodes Risks to Apis mellifera honey bees

There is a growing interest in finding sustainable alternatives to conventional chemical pesticides in order to protect both our environment and biodiversity. Entomopathogenic nematodes (EPNs) have been characterized as promising biological control agents, offering a safer approach to soil dwelling pest management. Going beyond soil applications, while protective formulations have shown some success, foliar application of EPNs is also gaining interest. Apart from the still open question of whether EPNs survive in the foliar environment and control pests effectively, there is also to be answered which are the potential effects on beneficial insects such as bees. This study investigates whether foliar application of EPNs poses a risk to honey bees (Apis mellifera). When 9 EPN species from the genera Steinernema and Heterorhabditis were tested, significant mortality was observed in honey bees, with Steinernema riobrave and Steinernema carpocapsae are particularly virulent. Two exposure methods (direct spraying and indirect filter paper) and three exposure periods (24, 48 & 72 h) resulted in higher bee mortality with the direct spraying method, attributed to direct contact with the nematodes and their infection, with all species to be significant virulent compared to control while only 1 out of 9 showed significance in filter paper experiment 72 hours after treatment. Dissection of dead bees confirmed the presence of nematodes, in the thorax and trachea. Furthermore, context-specific risk assessments, especially for foliar applications against plant pests, are crucial for developing sustainable agricultural practices that protect pollinator populations. This research contributes to understanding the ecological implications of EPNs use and emphasizes the need for a balanced approach that ensures food security while maintaining biodiversity.