Side effects of entomopathogenic nematodes on beneficial arthropods in pome fruit and the role of adjuvants on their selectivity

Abstract: Entomopathogenic nematodes (EPN) are increasingly being used as biological control of insect pests. Current applications are almost exclusively soil treatments, principally targeting soil-borne insect pests. However, the soil also harbours beneficial arthropods and less is known about the effects of EPNs on these soil-borne beneficial arthropods. Furthermore, there is a rising interest in their control potential of aboveground pests. Such aboveground treatments covering the crop with EPNs could also affect beneficial arthropods present on leaves and/or stem. In this study we investigate the side effects of EPNs (Steinernema carpocapsae, Steinernema kraussei, Heterorhabditis bacteriophora and Phasmarhabditis hermaphrodita) on two soil-borne beneficial arthropods in pome fruit, i.e. velvet mites (Allothrombium fuliginosum, Thrombidiidae) and earwigs (Forficula auricularia, Forficulidae) in laboratory trials. While S. carpocapsae and S. kraussei applied as sole treatment were only slightly to moderately harmful for both beneficial arthropods, significant increased mortality rates were obtained after EPN-treatments in combined use with adjuvant Trend90. Additionally, a field trial was carried out in which the impact of aboveground EPN treatments on several beneficial arthropods (including earwigs, predatory bugs and ladybirds) in apple was evaluated and compared to chemical references. In accordance with the laboratory trials no or only negligible side effects were obtained in absence of an adjuvant. These results demonstrate the rather safe use of EPNs in pome fruit orchards, but indicate potential side effects if EPNs are sprayed in combination.