SLU news

Winter survival of predatory mites that are used against pests is examined

Published: 28 May 2019

In greenhouses and in open-air crops, predatory mites are often used against thrips, dark-winged fungus gnats, and mites that damage the crops. But what happens if predatory mites, who do not usually live in Sweden, succeed in establishing themselves here? Currently, agronomist student Clara Kjellström is investigating whether the imported predators can survive the Swedish winter.

Predatory mites have been used since the 1980s in Sweden to combat pests such as thrips and mites, both in crops with vegetables, berries and in ornamental plants.

The Swedish Environmental Protection Agency approves nematodes, insects and arachnids

In 2019, a new system for the application and approval of species to be used as biological control agents was introduced in Sweden. The Swedish Environmental Protection Agency has taken over responsibility for approving nematodes, insects and arachnids for use as biological control agents from the Swedish Chemicals Agency.

– Today, four species of predatory mites are approved for use in greenhouses and in three of the cases in open-air cultivations, but two of them only have a time-limited approval until December 2022. For these species to be approved in the longer term, we need to have a better knowledge of which winter temperatures they can survive in. Of course, this determines if these species can establish themselves in Sweden, says Mattias Jonsson, director of the Center for Biological Control, CBC, at SLU.

Clara examines predatory mites in a dissecting microscope. Photo: Cajsa Lithell.
Microscope photo of the mouth pieces of the predatory mite Stratiolaelaps scimitus. Photo: Captainpixel, Wikipedia. CC 4.0.
Here, predatory mites in cans are put into a cabinet where the temperature will gradually go down to -20 degrees to simulate winter conditions. Will the predatory mites survive? Photo: Cajsa Lithell.

Clara Kjellström is studying the third year of the Agronomy program focused on soil and plants at SLU in Uppsala. She is doing her bachelor thesis at SLU in collaboration with the Swedish Environmental Protection Agency with Mattias Jonsson as supervisor.

– I think it is very interesting with biological control as part of integrated plant protection. This is becoming increasingly important as climate change increases the occurrence of pests and the use of chemical agents will be more restricted. In addition, it is much nicer for the growers to work with biological agents than with chemical pesticides. When it was time for my bachelor thesis, I wanted to do something related to biological control, Clara says.

Can predatory mites survive a Swedish winter?

In her bachelor thesis, Clara examines the winter survival of the terrestrial predatory mites Stratiolaelaps scimitus and Neoseiulus cucumeris. S scimitus is used against dark-winged fungus gnats and thrips and Neoseiulus cucumerisagainst thrips and mites.

– In the case of Stratiolaelaps scimitus, I do both practical trials and study literature, while for Neoseiulus cucumerisI only do a literature study. The latter species are tiny and has exactly the same color as the substrate they came in when we ordered the predatory mites. They were simply impossible to work with in this short project, Clara explains.

What will be the result of Clara's study?

– It seems that Stratiolaelaps scimitus dies already at 5-10 degrees below zero, Clara concludes.

In addition to studying to be an agronomist, Clara is the editor of the student newspaper Ultunesaren. This summer she will be an intern at the Swedish Board of Agriculture.

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