Patricia D. Navarro

The foraging behavior of the infective juveniles (IJs) of entomopathogenic nematodes (EPNs) relies on host-derived compounds, but in a tri-trophic context, herbivore-induced root volatiles act as signals enhancing the biological control of insect pests by recruiting EPNs. In southern Chile, the EPN Steinernema australe exhibits the potential to control the raspberry weevil, Aegorhinus superciliosus, a key pest of blueberry Vaccinium corymbosum. However, there is no information on the quality of the blueberry root volatile plume or the S. australe response to these chemicals as putative attractants. Here, we describe the root volatile profile of blueberries and the chemotaxis behavior of S. australe towards the volatiles identified from Vaccinium corymbosum roots, infested or uninfested with A. superciliosus larvae. Among others, we found linalool, α-terpineol, limonene, eucalyptol, 2-carene, 1-nonine, 10-undecyn-1-ol, and methyl salicylate in root volatiles and, depending on the level of the emissions, they were selected for bioassays. In the dose–response tests, S. australe was attracted to all five tested concentrations of methyl salicylate, 1-nonine, α-terpineol, and 2-carene, as well as to 100 µg mL⁻¹ of 10-undecyn-1-ol, 0.1 and 100 µg mL⁻¹ of linalool, and 100 µg mL⁻¹ of limonene, whereas eucalyptol elicited no attraction or repellency. These results suggest that some volatiles released from damaged roots attract S. australe and may have implications for the biocontrol of subterranean pests.

The entomopathogenic nematode (EPN) Steinernema australe was isolated from Isla Santa Magdalena in Chile and identified as a good alternative for controlling Aegorhinus nodipennis (Coleoptera: Curculionidae) larvae. This weevil is native to the south of Chile and some regions in Argentina, causing the decline and ultimate death of plants in berry orchards. The major problem brought about by the weevil is caused by the larvae, which spend between nine and eleven months below ground, feeding inside the roots of the plants. This study seeks to increase S. australe’s efficacy through an artificial selection process using an odor stimulus. We selected infective juveniles (IJs) that followed the stimulus in order to reach larvae at a depth of 30 cm to achieve this objective. Larvae infected with selected IJs and IJs from the original stock were compared under laboratory, greenhouse, and field conditions. The results showed a 20% increase in the efficacy of selected IJs compared with IJs from the original stock. We observed a higher proportion of selected IJs that reached the larvae faster during the first four days post-application. Moreover, larvae treated with selected IJs were depleted, with a mix of nematode stages emerging from the cadaver. Finally, a potential trade-off with regard to the recycling of nematodes into the soil is proposed.