Comparative susceptibility of larval instars and pupae of the western corn rootworm to infection by three entomopathogenic nematodes

As a first step towards the development of an ecologically rational control strategy against western corn rootworm (WCR; <i>Diabrotica virgifera virgifera</i> LeConte, Coleoptera: Chrysomelidae) in Europe, we compared the susceptibility of the soil living larvae and pupae of this maize pest to infection by three entomopathogenic nematode (EPN) species. In laboratory assays using sand-filled trays, <i>Heterorhabditis bacteriophora</i> Poinar and <i>H. megidis</i> Poinar, Jackson & Klein (both Rhabditida: Heterorhabditidae) caused comparable mortality among all three larval instars and pupae of <i>D. v. virgifera</i>. In soil-filled trays, <i>H. bacteriophora</i> was slightly more effective against third larval instars and pupae, and <i>H. megidis</i> against third larval instars, compared to other developmental stages. In both sand and soil, Steinernema feltiae (Filipjev) (Rh.: Steinernematidae) was least effective against second instars. In conclusion, all larval instars of <i>D. v. virgifera</i> show susceptibility to infection by all three nematodes tested. It is predicted that early application against young larval instars would be most effective at preventing root feeding damage by <i>D. v. virgifera</i>. Applications of nematodes just before or during the time period when third instars are predominant in the field are likely to increase control efficacy. According to our laboratory assays, <i>H. bacteriophora</i> and <i>H. megidis</i> appear to be the most promising candidates for testing in the field.