Evaluation of application technologies of entomopathogenic nematodes for control of the black vine weevil

Black vine weevil, Otiorhynchus sulcatus (F.), is a severe pest of small fruit and nursery crops around the world. These studies were conducted to determine the efficacy of three species of entomopathogenic nematodes (Heterorhabditis marelatus, Heterorhabditis bacteriophora, and Steinernema riobrave) applied in infected host cadavers or as aqueous applications for black vine weevil larval control. Experiments were conducted in the greenhouse and outdoors. Application of three infected host cadavers or 40 infective juvenile nematodes (IJs) /cm2 were made to pots of Impatiens walleriana 5-7 d after larval infestation. Efficacy was assessed at 14 d in the greenhouse and at 14 and 28 d after nematode application in outdoor trials. In the greenhouse, all treatments with the exception the S. riobrave (cadaver and aqueous applications) provided nearly 100% efficacy after 14 d. The S. riobrave applications, although significantly better than the control, only provided 40-70% control and were not included in the outdoor trials. Nematode efficacy was slowed in the outdoor trials particularly in the cadaver applications. In the initial outdoor trial (soil temperatures < 12 degrees C), there were no significant differences between any nematode treatment and the control after 14 d. The nematode efficacy in the initial outdoor trial after 28 d was improved from the 14-d evaluation but not to the level seen in the second trial. In the second outdoor trial, in which soil temperatures were higher (> 12 degrees C), the aqueous applications of H. marelatus and H. bacteriophora provided nearly complete control after 14 d. The cadaver applications also provided nearly complete control in the second outdoor trial after 28 d. Even though the potential total number of IJs estimated per pot was higher in the cadaver-applied treatments, cool soil temperatures apparently delayed or potentially reduced IJ emergence from cadavers resulting in delayed control.