Report no: 2010: 08
There is a high probability that the three leafminer species Liriomyza huidobrensis, L. trifolii and L. sativae in the future will be imported into Norway through infested plants and establish populations in greenhouses. Without today’s phytosanitary regulations these species might spread quickly over the whole country. These are the main conclusions in the risk assessments prepared by VKM for the three Liriomyza species in Norway.
The South American Leafminer (L. huidobrensis), the American Serpentine Leafminer (L. trifolii) and the Vegetable Leafminer (L. sativae) are quarantine pests forbidden to introduce and spread in Norway. L. huidobrensis and L. trifolii have several times been detected in Norwegian greenhouses, but have been eradicated each time.
Liriomyza causes damage on a wide range of greenhouse crops. Adults copulate on the host plants, and the females make so-called pinholes by inserting their ovipositor into the leaves to feed on the plant fluids that run from the wounds. Later they lay eggs inside the leaf in some of the pinholes.
Larvae hatch from the eggs and create a so-called mine by eating tissue inside the leaf. When fully grown, the larvae leave the mine and pupate either on the outside of the leaf or drop to the ground before they pupate. The next generation of flies emerges from the pupae.
Thus, the plant host species offers the flies all they need concerning environment and development. A small infestation can be difficult to discover, since it often can consist only of pinholes, eggs and possibly some larvae in small mines. Also, sometimes the mines are easy to spot from only one side of the leaf, and can easily be overlooked.
VKM’s Panel on plant health has initiated the risk assessments of the three leafminer species L. huidobrensis, L. trifolii and L. sativae. Earlier risk assessments of the same species have been made by Bioforsk in 1996. Since then these plant pests have established in many countries, and two of them have been detected in Norway several times.
There is a high probability that L. huidobrensis, L. trifolii and L. sativae again will enter Norway through infested plants and establish populations in greenhouses. The most probable pathway of entry is import of host plants carrying eggs, larvae, pupae or flies.
Without phytosanitary regulations the Liriomyza leafminers might spread quickly via infested host plants to greenhouses over the whole country.
The leafminers might also spread outdoors, but they will not survive the winter outdoors in Norway. Even with today’s regulations these pests have the potential to cause moderate economic loss for the greenhouse industry.
An ad hoc-group consisting of both VKM members and external experts was appointed by the Panel on plant health to prepare a draft for final adoption by the panel. The members of the ad hoc-group are acknowledged for their valuable contribution. The members of the ad hoc-group were: Trond Hofsvang (VKM member) og Arild Andersen (eksternal expert, Bioforsk).