Drosophila suzukii population dynamics and control efficiency of mineral dusts with a focus on grape protection.
The invasive pest Drosophila suzukii is threatening berry production. It is mainly managed via chemical control, which is associated with consumer and environmental concerns. Here, we tested the efficacy of mineral dusts under field and laboratory conditions in 2019 and 2020. Furthermore, population dynamics were studied in a vineyard and its surroundings. The kaolin products Cutisan and Surround®, as well as the CaCO3 product Carboliq, had neither insecticidal nor repellent effects on Drosophila suzukii adults in laboratory choice tests with grapes at concentrations of up to 2% (w/v). Cutisan and Surround® significantly reduced the number of deposited eggs (-41.9% and -49.3% respectively) while Carboliq had no effect on the oviposition under laboratory conditions. The Surround® treatment significantly reduced the number of flies trapped on 09 September 2020 at a test vineyard. Depending on the assessment date and treatment, between 59% and 84% of the flies in the bait traps were females. The number of eggs found in fruit treated with Carboliq in the field was higher at each assessment date than in the control but this difference was not statistically significant. Fruit treated with Cutisan or Surround® in the field showed an equivalent or lower average number of eggs compared with the control, but this difference was only significant on 24 September 2020. Between May 2015 and October 2020, the highest number of D. suzukii adults was observed around September in the field and a decline of the population occurred in the winter months until July. In epidemic years, temperature - humidity - combinations prior to population peaks were quite stable with low humidity being associated with a high temperature and vice versa. In non-epidemic years, humidity fluctuated more than in epidemic years and temperatures were lower before population peaks. The effect of global radiation on population maxima seemed to be minor.