Application of Steinernema yirgalemense to control Frankliniella occidentalis (Thysanoptera: Thripidae) on blueberries

Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) (WFT) is one of the most economically important insect pests in undercover blueberry production. There is a need for biological control of WFT in South Africa, due to the rapid growth of the blueberry industry. The effect of the application of high and low concentrations of a local entomopathogenic nematode (EPN), Steinernema yirgalemense, in controlling F. occidentalis on naturally infested, commercially produced blueberries in potted plants, grown in polytunnels, was investigated. Two trials, one evaluating EPN concentrations of 4.3, 8.6 and 17.2 IJs/cm2 and second trial with concentrations of 25, 50 and 100 IJs/cm2, were conducted on naturally WFT-infested plants, which were each individually enchased in netting. Blue sticky pads, inside the netting with each plant, were used to monitor the WFT populations, after the applications of nematodes to the whole plant and the surface of the potting medium. At the same time persistence of the nematodes in the potting medium was tested, by weekly trapping with mealworm larvae. The second experiment using higher nematode concentrations, showed increased thrips mortality (53%) in relation to the first experiment with lower concentration (<40%). The low nematode infection of WFT may be ascribed to the long periods of suboptimal temperatures (≈16 °C) experienced during the 4-week exposure trial period. Future studies should target WFT on the new growth, just after summer pruning, when thrips populations tend to peak and cause significant economic damage. The application of S. yirgalemense to the soil/growth substrate of blueberries in polytunnels, when warmer environmental temperatures prevail, as well as higher concentrations with more frequent nematode application, warrant further investigation.