Valuable seed destroyed by insects

Damage by cone and seed insects is a severe impediment to those producing conifer seeds in seed orchards. The SNS-supported network "Nordic cone and seed insects" has been cooperating to address this problem since 2007. One of the outcomes is the coordinated monitoring of the most important insect species. The data collected form a basis for establishing strategies for pest management.

Seeds from seed orchards are the most valuable product per unit volume in forestry. Spruce seeds from seed orchards not only have a high market value (€1 000–1 500/kg), but trees derived from these seeds ensure higher growth rates and better wood quality. Insect damage has been reported to cause over 90% loss of the expected seed yield from orchards in the Nordic countries. A review of Swedish cone sampling protocols between 1983 and 2004 showed an average infestation rate of 40%. 

The problem with seed- and coneeating insects is common to all Nordic and Baltic countries. In Denmark, the economic losses are highest in seed orchards of Abies species, while Norway spruce suffers the most severe problems in Norway, Sweden, Finland and the Baltic states.

The Nordic Cone and Seed Insects network has been active since 2007. It draws together expertise in the area to discuss experiences and to find management options that will help to prevent more seed from being destroyed. Coordination of the network has circulated among the members. Currently, Dr Olle Rosenberg of the Forestry Research Institute, Sweden (Skogforsk) is in charge. He is optimistic about the chance of finding management solutions. But he is also pragmatic about all the questions that remain to be answered.

– With joint efforts, we now have a much better knowledge of the most important pests, and we also have a good range of experience of some of the measures that can be adopted to combat them, he says.

One of the major cone insects is the spruce cone worm, Dioryctria abietella. This species was the focus when the network was established. A common protocol for monitoring the species in seed orchards was set up, and has resulted in a mass of data about when and where the insect appears.

Monitoring with pheromone traps

Monitoring of the spruce cone worm has been going on, more or less without interruption, since 2007 in Denmark, Sweden, Finland and Norway, and since 2009 in Estonia.

– The flight period is relatively long, from late May to late August, although some individuals have been captured in late September. The start of the flight period is very dependent on temperature. The information we gain might in the future help us to predict when protective measures are necessary, says Olle Rosenberg.

A prerequisite for successful monitoring was the availability of a synthetic pheromone, specific to the spruce cone worm. The pheromone was developed by researchers at the University of Lund in collaboration with Skogforsk, INRA in France and the University of California. The pheromones attract adult males of the moth to the trap.

While Dioryctria abietella was the first species to be studied, the network has gone on to study the spruce seed worm, Cydia strobilella. A pheromone for this species was developed in a cooperative project involving Skogforsk and the University of Lund. Coordinated monitoring of Cydia strobilella is currently going on in Sweden, Finland and Estonia.

Biological treatment

For over a decade, Skogforsk has been testing and developing a biological treatment using Bacillus thuringiensis var kurstaki/aizawai (Btk). The bacteria produce poisonous substances which kill the moths in the cones. The results have so far been successful, with a reduction in the number of damaged cones to a third, all at a reasonable cost.

Other treatments involve chemical insecticides, which are used on a trial basis. The ongoing struggle to reduce pesticides in the EU calls for integrated pest management strategies. Monitoring is thus a help to avoid unnecessary pesticide applications.

Results from the Nordic cone and seed insect network have been reported at various international conferences. The intention now is to assemble the experiences into a review paper on cone and seed insects and to produce another paper about the monitoring conducted in the Nordic countries.

Contacts: 

Olle Rosenberg, Skogforsk, Sweden olle.rosenberg@skogforsk.se
Tiina Ylioja, Metla, Finland (tiina.ylioja@metla.fi)
Hans Peter Ravn, University of Copenhagen, Denmark (hpr@life. ku.dk)
Paal Krokene, Norsk Institutt for skog og landskap, Norway (paal.krokene@skogoglandskap.no)
Kaljo Voolma, Estonian University of Life Sciences, Estonia (kaljo.voolma@emu.ee)

From News and Views no 1, 2012 (www.nordicforestresearch.org)