Control of Diaprepes abbreviatus (Coleoptera: Curculionidae) with Steinernema riobrave (Rhabditida: Steinernematidae) in plasticulture Florida strawberry

Diaprepes abbreviatus L. (Coleoptera: Curculionidae) is an occasional root pest of plasticulture strawberry in central Florida, USA. There are few chemical insecticide options for larval D. abbreviatus in strawberry. Therefore, we tested soil-applied aqueous Steinernema riobrave Cabanillas, Raulston and Poinar (Rhabditida: Steinernematidae), which is used for D. abbreviatus control in citrus. When S. riobrave was applied (100 infective juveniles per cm2) to the root zones of plants in a D. abbreviatus-affected area of a commercial strawberry field, less than 12% of plants were severely wilted or dead 17 d after treatment, whereas 23% of plants in control plots were wilted or dead. In research plots, peripheral plants and a central plant in each plot were infested with 4 late-instar D. abbreviatus and treated with 1 or 2 applications of S. riobrave (25 infective juveniles per cm2), 1 application of imidacloprid or water (control). Dead S. riobrave-infected D. abbreviatus larvae were recovered from plots to which S. riobrave was applied, but there was no effect of treatment on numbers of live larvae recovered 1, 2, and 3 wk post-application in the peripheral plants. At the end of the experiment, no live D. abbreviatus larvae were recovered from the central plants or the plants proximal to the central plants in plots treated once or twice with S. riobrave. Plant wilting and death due to larval D. abbreviatus root feeding was minimal (averages of 1–1.4 on a 1–5 rating scale) in plants proximal and distal to the central D. abbreviatus-infested plant. Treatment did not affect plant wilting and death rates in the proximal plants, but death of distal plants occurred only in control plots. Our results showed S. riobrave infected and killed late-instar D. abbreviatus in plasticulture Florida strawberry, and further research should be conducted to optimize S. riobrave applications and develop it into a management strategy for D. abbreviatus.