Overview of research
In 2004 and 2005, the Wageningen UR Greenhouse Horticulture carried out research into the use of a series of new predatory mites in roses. This research focused primarily on the establishment of these predatory mites in the presence of spider mite and glasshouse whitefly infestations. A. swirskii was one of the new species of predatory mite that showed good results. If just glasshouse whitefly was present, A. swirskii was able to establish itself, and the population built up well. In addition, the population was well dispersed through the crop (see graph 1). High densities were reached in the rose bed in which A. swirskii had been released up to an average of five predatory mites per leaf. Despite these high densities, the control of the glasshouse whitefly was not sufficient in this trial. For complete control, a combination with the parasitic wasps Encarsia formosa and Eretmocerus eremicus together with integratable agents is probably necessary.
A. swirskii was also able to establish itself well when spider mite was present (see graph 2), although not in such high densities as in the presence of glasshouse whitefly. A. swirskii appears to be able to clear low densities of spider mite. A. swirskii is less adequate in combating dense hot-spots of spider mite. In such cases, help is needed from real hot-spot clearers like Phytoseiulus persimilis and Feltiella acarisuga.
A. swirskii appeared to be able to establish itself all year round in a crop of roses. Even in the winter, with virtually no infestations, A. swirskii was one of the few species that were still easy to trace in the crop. On the basis of these results, it can be stated that A. swirskii could make an important contribution to combating whitefly and spider mite in roses. The predatory mites are able to establish themselves well and build up a large population in a crop of roses. However, this build-up of the population takes place much slower than in a crop like cucumber. It is still unclear to what extent A. swirskii can have an effect on thrips in roses.
Koppert has tested A. swirskii in roses in four practical trials. In the first trial, A. swirskii was released in and around hot-spots of glasshouse whitefly. Two trials looked at different dosages, and in the last trial A. swirskii was compared with Amblyseius cucumeris. The trial looking at dosages led to the conclusion that the supply of food in the crop has the most influence on the numbers of A. swirskii that can be found in the crop.
In the trial comparing A. swirskii with A. cucumeris, both species of predatory mite were released into the crop from slow-release bags (see graph 3). There was scarcely any whitefly or spider mite. The trial then looked at which predatory mite was found in the largest numbers in the crop. The population in the crop turned out to consist of 90% A. swirskii and 10% A. cucumeris.
Results
A. swirskii can establish itself well in rose crops.
A. swirskii is much easier to find in the rose crop than A. cucumeris
A. swirskii has a controlling effect on whitefly and a side effect on spider mite
See graph 1 Establishment of A. swirskii in rose crops in the presence of spider mite
See graph 2 Comparison of A. swirskii with A. cucumeris (percentage of leaves with predatory mites).
