The efficiency of the newly launched predatory mite Amblydromalus limonicus : biological control of thrips in cucumber

Abstract: In this study, the efficiency of a newly launched predatory mite, Amblydromalus limonicus, has been examined for its potential to use as a biological control agent in cucumber production. A. limonicus can be used for biological control of two thrips species, Frankliniella occidentalis and Thrips tabaci. Field trials were conducted in greenhouses of two conventional cucumber growers in Scania, the southern part of Sweden. The basic control agent used against thrips was the predatory mite Amblyseius swirskii. In selected areas, additional A. limonicus was released. A. limonicus were released twice after the transplantation of the second crop in a dose of 100 predatory mites per square meter, with a two week interval. The thrips population was monitored in three ways during the season; counting of trips caught on blue sticky traps and counting of thrips found in the flowers and on the leafs. The results indicate that the thrips population on plants decreased when both predatory mites, A. swirskii and A. limonicus, were released. The overall low thrips infestation may have contributed to a negative interaction between A. swirskii and A. limonicus, due to cannibalistic behavior. Following the second release of A. limonicus, a lower total density of predatory mites were found. The area treated with only A. swirskii had a higher total predatory mite density which indicates that A. swirskii is efficient at this level of pest infestation. One of the growers leaves the greenhouse empty for two weeks between the two cultures. Following this period the population of F. occidentalis decreased to a low level. This raises the question whether this kind of treatment can be useful in an integrated pest management strategy.