Work

The enemy of my enemy is not always my friend: Susceptibility of honey bee to entomopathogenic nematodes

Year: 2025

Type: article

Abstract: Entomopathogenic nematodes (EPNs) are effective biocontrol agents against soil-borne insect pests, yet the risks they pose for beneficial insects are understudied, particularly when applied outside the soil. With growing interest in above ground applications of EPNs such as on crop foliage or against pests of the western honey bee (Apis mellifera) in hives, it is essential to evaluate their effects on honey bees. We conducted a large-scale assessment of honey bee brood and adult worker susceptibility to Australian isolates of the EPN genera Heterorhabditis and Steinernema ex situ (filter paper bioassays in Petri dishes) and in situ (application in combs and subcolonies). At 25 °C, filter paper bioassays showed that late instar honey bee larvae were highly susceptible to all EPN isolates, with Heterorhabditis indica (particularly isolates Hi.HRN and Hi.HRN2) being the most virulent. Increasing the assay temperature to 33 °C reduced virulence across isolates, yet all remained pathogenic. Similarly, adult workers were highly susceptible, again with Hi.HRN2 showing the greatest virulence. Conversely, Steinernema feltiae (notably isolate Sf.CPBR2) was the least virulent species, although it was still capable of causing high mortality in both larvae and workers. Interestingly, parasitisation of honey bee larvae by Varroa destructor increased susceptibility to Sf.CPBR2 but not to Hi.HRN2. Under hive-like conditions, direct treatment of uncapped and capped bee cells with Hi.HRN2 resulted in <50% larval and <33% pupal mortality. Finally, Hi.HRN2 treatment of subcolonies caused 24% brood and 16% adult worker mortality. Overall, our results indicate that above-ground applications of EPNs require precautionary measures to safeguard honey bees, particularly when used in agroecosystems during honey bee foraging periods or in hives against honey bee pests.

Source: Journal of Invertebrate Pathology

DOI: 10.1016/j.jip.2025.108524