Management of black vine weevil (Otiorhynchus sulcatus) by entomopathogenic nematodes in Georgia

Abstract: The aim of this study was to determine the biological control effect of entomopathogenic nematodes species, Steinernema carpocapsae and Steinernema feltiae against Otiorhynchus sulcatus. Adult weevils can be controlled by using nematodes, as biocontrol. Also grubs can be controlled using the fungus Beauveria bassiana. Experiments were evaluated under laboratory conditions. Various laboratory bioassays were conducted to determine the effectivity of entomopathogenic nematodes to control Otiorhynchus sulcatus. Adult O. sulcatus were screened for susceptibility to two introduced from Israel nematode species. Otiorhynchus sulcatus was found to be most susceptible to Steinernema carpocapsae and Steinernema feltiae, causing mortality 34, 52, 83% and 27, 34, 69% on the temperature 25 °C and 1000 IJs/ml cm2 concentration, respectively. Larvae of Otiorhynchus sulcatus were controlled using the fungus Beauveria bassiana. As fungus Beauveria bassiana would be used as an above-ground application to control O. sulcatus in grape orchards. Fungal isolate Beauveria bassiana was applied by pipetting 25 μl of the conidia suspension onto the back of each larva while in the wells, i. e. 2.5 × 105 conidia per larva. Larvae were examined for mortality once a week for four weeks after inoculation. Further bioassays illustrated a linear relationship between black vine weevil, mortality and the concentration of nematodes applied, with the highest level of control using a concentration of 1000, 1500 infective juveniles (IJs)/insect. Steinernema carpocapsae proved able to locate and infect black vine weevil, quicker, than Steinernema feltiae. For all nematode species, the highest virulence was observed 48, 56, 88% and 39, 45, 78% on the temperature 25 °C and 1500 IJs/ml cm2 concentration for S. carpocapsae, and S. feltiae, respectively. Fungal isolate Beauveria bassiana imposed more, than 50% larval mortality of Otiorhynchus sulcatus. In conclusion, it was determined that Otiorhynchus sulcatus can be controlled by S. carpocapsae, S. feltiae and fungus Beauveria bassiana, but further studies should be conducted at field conditions.