Sammendrag
Key words: apiculture, biological control, Norwegian Environment Agency, Norwegian Scientific Committee for Food and Environment, predatory mites, risk assessment, varroa
Introduction
The Norwegian Environment Agency (NEA) have asked the Norwegian Scientific Committee
for Food and Environment for an assessment of adverse impacts on biodiversity concerning
import and release of the predatory mite Stratiolaelaps scimitus as measure against varroa
mites (Varroa destructor) in apiaries.
The predatory mite is already in use in Norwegian greenhouses and polytunnels as a
biological control agent against dark-winged fungus gnats in a various of plant cultures.
The NEA has received an application for a new type of use: to combat varroa mites in
apiaries.
Background
Varroa destructor (the varroa mite) is a species of parasitic mite that feeds externally on
honeybees; it is considered one of the major threats to beekeeping world-wide due to its
parasitic behaviour and because it acts as a vector for several viral and bacterial bee
pathogens. Beekeepers in North America have begun experimenting with introducing
Stratiolaelaps scimitus, a commercially available predaceous mite originally used for
biocontrol in greenhouses and polytunnels, to control varroa mites, and several studies on
the use of the mite in this context have been published recently. The Norwegian
Environment Agency has asked VKM to assess the risk to biological diversity in Norway
associated with this new use of S. scimitus, and to assess the effects of climate change on
any risks that are proposed.
Stratiolaelaps scimitus is a tiny (0.5 mm), soil-dwelling predaceous mite that in nature feeds
on a wide variety of soil invertebrates, including fly larvae, nematodes, nymphs of thrips,
potworms (oligochaetes), springtails, and other mites. For over three decades, Stratiolaelaps
scimitus has been produced commercially and the species is now used globally for biological
control. The mite is applied to control a wide variety of organisms harmful to food production
or to the production of ornamental plants, but especially to combat infestations of fungus
gnat larvae, spider mites, flower thrips, and certain plant-feeding nematodes. The species is
already used as a biocontrol agent in Norway in greenhouses, open plastic polytunnels used
for protecting crops, and in various indoor plantings and fungiculture.
Methods
VKM established a project group with expertise in entomology, invasion ecology, honeybee
behaviour and ecology, and risk analysis of biological control agents. The group conducted
systematic literature searches and scrutinized the relevant literature that was found. In the
absence of Norwegian studies, VKM relied on literature from other countries.
Results and conclusions
This VKM assessment concludes with medium confidence that introducing S. scimitus for use
in beehives would not significantly increase the probability of establishment and spread of S.
scimitus above that of its current use. We point out that there is no evidence that continuous
use of S. scimitus in Norway, over decades, has led to its establishment outside of
enclosures, including open polytunnels. The optimal temperature for development and
reproduction is far higher than what is normally observed in Norway (~28 °C). Although
lethal temperature has been reported to be as low as –5.2 °C, we still conclude that S.
scimitus would not be able to establish permanent populations in Norway, not even in the
southern part of the country as such temperatures are expected to occur in some years
throughout the country. Future climate change is not believed to alter this conclusion, since
periods with lethally cold temperatures are expected to still occur in the future.
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