Entomopathogenic nematodes can replace soil insecticides in western corn rootworm control

Abstract: In an attempt to replace insecticides against the maize-root feeding larvae of the western corn rootworm (Diabrotica virgifera virgifera, Coleoptera: Chrysomelidae), biological control solutions based on entomopathogenic nematodes have been developed. Currently, the fluid application of the living nematodes into the sowing furrow is the most developed and validated application technique. This study investigated whether fluid applications of Heterorhabditis bacteriophora (Nematoda: Rhabditida) can be an alternative to older as well as recently registered synthetic soil insecticides in the management of established D. v. virgifera pest populations in maize. Five field trials were therefore implemented in southern Hungary between 2013 and 2015 using growers` machinery. Results revealed that all agents tested, regardless of biological or chemical, were able to reduce adult emergence of D. v. virgifera; but none is highly effective. However, entomopathogenic nematodes can, if applied at a relatively high dosage, be as effective as the synthetic soil insecticides in controlling the larvae. All agents were in most occasions also able to significantly prevent some of the root damage caused by D. v. virgifera larvae. As for economic root damage (node injury scale data), Tefluthrin soil granules best prevented such heavy root damage followed by the nematodes; whereas Cypermethrin and Chlorpyrifos soil granules were usually not able to prevent heavy root damage. Nematode treatments as well as soil insecticides slightly increased yield. In conclusion, the recommended commercial dose of 2 billion nematodes per hectare appeared likely to be enough for pest management in most cases; this is, keeping D. v. virgifera and damage below thresholds. This is, however, only true when nematodes are correctly applied and when D. v. virgifera infestations are significant. To assure a higher security in treatment efficacy across locations, conditions, and different grower skill-levels, a higher dose might be applied. Findings support a nematode-based solution for the biological control of D. v. virgifera larvae in maize fields in European regions as one among the alternative options to replace synthetic insecticides.