Of pests and their enemies

Experts from Land and Forest Iceland, Dr. Brynja Hrafnkelsdóttir and MSc. Helga Ösp Jónsdóttir, are collecting information about damage to trees and shrubs around the country, whether the damage is caused by insects, fungal diseases or other threats, but also damage caused by other factors, such as the cold weather that hit the country in early June, or other shocks. Information can be sent to their email addresses, brynja.hrafnkelsdottir@landogskogur.is, or helga.o.jonsdottir@landogskogur.is.

Brassy leaf beetle

There have been growing reports of the brassy leaf beetle spreading in Iceland in recent years. Last summer, tea-willow (Salix phylicifolia) bushes in Reykjadalur in Northeast Iceland were quite noticeably damaged by the brassy leaf beetle, according to Þorbergur Hjalti Jónsson, an expert at Land and Forest Iceland, who lives in the area. This summer, however, he notices the same bushes appearing green and lush with no evidence of the beetle or its larvae. In contrast, this summer for the first time, a prominent damage of the brassy leaf beetle has been noticed in the town of Akureyri and in its vicinity. Close to the airport for example, some bushes of tea-leaved willow have turned completely brown due to the attack from the beetle, as shown on the photo below.

This shift from last year is somewhat surprising. One possible explanation suggested by the experts is that the cold weather that hit the country in early June may have hit harder in Reykjadalur than in Akureyri. That might have prevented the brassy leaf beetle from gaining ground in Reykjadalur this summer.

It should also be noted that the insect species common flowerbug (Anthocoris nemorum) has been found feeding on the beetle's larvae and eggs. That may have played a role in the reduced impact of the brassy leaf beetle. Common flowerbug was first discovered in Iceland in 2007 and has been found widely in the capital area and in several places in North Iceland in the past few years. The larvae of the brassy leaf beetle produce toxins that deter most of its potential predators. For example, knowledge of instances of birds feeding on the brassy leaf beetle does not seem to be at hand, neither its larvae nor its beetles. Below is a photo of a common flowerbug found in Akureyri last August.

The poplar leaf rust fungus

Other findings that have been made this summer are that rust fungi do not seem to be hitting hard in the north of Iceland this summer, neither on black cottonwood nor downy birch. Little evidence is of the poplar leaf rust fungus Melampsora larici-populina in Akureyri and the surrounding area for instance. Similarly, there is also little evidence of birch rust so far, despite the heavy rainfall in June and August. As for the poplar leaf rust fungus, which uses larch as secondary host, one possible explanation of the fact that the fungus hasn't managed to spread much this summer is also the aforementioned weather event in early June. The exceptionally low temperatures may have influenced and hampered the natural cycle of the fungus, thus preventing it from thriving this summer.

Lupin pests

In South Iceland, recent observations indicate that three previously reported predators of lupins remain active and thriving. These domestic insect species, namely the rusty tussock moth (Orgyia antiqua), the broom moth (Ceramica pisi), and the satyr pug (Eupithecia satyrata), have a long history in Iceland. While the first two species were initially confined to South Iceland, their distribution and population growth have expanded in recent decades. Þorsteinn Kristinsson, an IT specialist at Land and Forest Iceland based in Gunnarsholt, recently observed and documented the presence of all three predators on a single lupin plant. These observations align with the findings of Dr. Brynja Hrafnkelsdóttir, who has conducted extensive research on these insects, particularly the broom moth. Her doctoral thesis, completed in 2020, explores the interactions between native grazing insects, introduced plant species, and climate change in the Icelandic context.

Is the birch recovering?

Recently, there has been an increase in the spread of new pests that have been affecting birch trees across the nation. These pests include the white-spotted spring-jewel (Heringocrania unimaculella) and the sawfly Scolioneura betuleti. Both of these species lay their eggs within the leaves of birch trees, where their larvae are protected from predators such as birds. Fortunately, there have been some positive developments in the fight against these pests. Last year, a parasitic wasp species was observed feeding on the larvae of the sawfly. This natural enemy of the sawfly has now been found in Eyjafjörður, indicating that it is spreading across the country. While it is still too early to determine the exact reasons for the decrease in damage to birch trees in southwest Iceland, it appears that the presence of this parasitic wasp may be a contributing factor. However, it is important to note that severe damage is now being observed in Akureyri and the surrounding area. In South Iceland, Ms. Brynja and Ms Helga Ösp have observed positive indicators of recovery this summer. This suggests that the initial surge in pressure often associated with new pests may be beginning to diminish. Alternatively, it is possible that a new adversary is significantly impacting these pests in the southern regions, and a similar effect can be anticipated in the northern areas in the coming years.

Information requested...

... on pests

We would be grateful to anyone able to provide us with any information people may have regarding any damage to trees, shrubs, or other types of plants that may have occurred during the summer months due to pests.

... on seed development in trees

Furthermore, we are gathering data on the seed development of various tree species. The annual nationwide collection of birch seeds is imminent, and it is important to identify the most suitable regions for seed collection this year. Additionally, seeds of spruce, pine, and potentially larch, as well as other tree species, will be collected for sowing in plant nurseries. We would greatly appreciate any information regarding the status of tree seeds or ongoing efforts to collect them.