The artificial selection process using an odor cue enhances the efficacy of the entomopathogenic nematode Steinernema austral against Aegorhinus superciliosus weevil larvae in berry orchards

The entomopathogen nematode (EPN) Steinernema australe was first isolated in Chile and identified as a good alternative for controlling Aegorhinus superciliosus (Coleoptera: Curculionidae) larvae. This weevil is native to southern Chile and certain regions in Argentina, causing berry orchards to decline and die. The major problem is caused by the larva, which spends between nine and eleven months below ground and feeds inside the root, making galleries. This study seeks to increase S. australe’s efficacy through an artificial odor stimulus selection process. We selected S. australe infective juveniles (IJs) that follow the stimulus and reach the larva at 30 cm deep faster. Larvae infected with selected IJs and IJs from the original stock were compared under laboratory, greenhouse, and field conditions. Insect mortality and EPN penetration were analyzed using ANOVA with the number of dead larvae and IJs that penetrated the larvae as response variables. Results showed a 20% increase in the efficacy of selected IJs compared with IJs from the original stock. The most remarkable effect of the selection process on S. australe was the increase in the proportion of IJs that reached the larva faster, vertically down in the soil, during the first four days post-application. Moreover, larvae treated with selected IJs were depleted, showing a mix of nematode stages emerging from the cadaver. A potential trade-off on nematodes’ recycling in the soil is proposed. This is the first report focusing on the effect of artificial selection to increase the efficacy of S. australe in the field.