Entomopathogenic nematodes applied as infected Galleria mellonella cadavers against wireworms (Coleoptera: Elateridae)

Wireworms (Coleoptera: Elateridae), are pests of cereal crops in Montana, USA. Because of lack of effective control measures, alternative control methods such as biological control with entomopathogenic nematodes (EPNs) are needed. EPNs are normally applied in aqueous suspensions but can also be applied in form of EPN-infected host cadavers. Imidacloprid, a prophylactic seed treatment insecticide causes short term suppression of wireworms. This study was focused on measuring efficacy of EPNs applied via Galleria mellonella L. (Lepidoptera: Pyralidae) cadavers in conjunction with imidacloprid seed treatment against sugarbeet wireworm, Limonius californicus (Mannerheim) in field and greenhouse. Galleria mellonella cadavers were prepared by inoculating live larvae with 200 freshly produced EPN infective juveniles. None of the EPN strains tested were found effective in terms of reducing wireworms and protecting crop yield in field. When applied with imidacloprid treated wheat seeds in greenhouse, one G. mellonella cadaver infected with Steinernema carpocapsae (All and Cxrd strains) or S. riobrave 355 killed 50-68% of L. californicus. The mortality range was 40-56% for S. carpocapsae (All and Cxrd strains) and S. riobrave 355 when seeds were planted without imidacloprid, not differing significantly from imidacloprid treatment (but higher than control). However, plant damage was significantly lower in imidacloprid treated plants (8-24%) as compared to non-imidacloprid plants (57-75%) at 35 days after treatment (DAT). Limonius californicus larvae reduced 57% and 92% of non-imidacloprid plants at 14 and 35 DAT, respectively. EPN alone treatment was not found as effective as the combination of imidacloprid and EPN treatments in greenhouse.