Insect pests of trees
In the last 50 years insect pests of conifers have declined but insect pests of deciduous trees have increased. This is the result of the change in the composition of Dutch forest.
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Trends
From the top 10 of insect plagues in the Netherlands it can be seen that insect pests of conifers have declined but insect pests of deciduous trees have increased. This is related to the increase in deciduous trees in Dutch forests and the dwindling area of young coniferous stands. The insect species responsible for infestations between 1950 and 1970 are nearly all species that live on softwood, like the common pine sawfly. Post 1980, the pest species live mainly on deciduous trees (for example, the two-spotted oak borer).
Since1946, 350 insect species have been recorded as pests in the Netherlands. The top 10 gives only the most common. In 2000 these were (starting with number 1): the horse-chestnut leaf miner, the oak procession moth, horse-chestnut scale, goat moth, Dutch elm beetle, woolly beech aphid, spindle ermine moth, green oak tortrix moth, bird-cherry ermine moth and two-spotted oak borer.
Pest insects often cause economic damage to crops and trees. Insect infestations in forests are a natural phenomenon that is aggravated by the planting of monocultures. But given that forest management is now aimed at producing more mixed forest and thus at reducing the monocultures, it is expected that the plagues will become less severe.
Technical note
Insect infestations on trees and shrubs have been monitored annually in the Netherlands since 1946 by a national network of volunteers. A top 10 of the observations of insect damage to trees and shrubs has been compiled for each 5-year period. The figure shows the number of species of coniferous and deciduous trees appearing in this top 10. The sum of the number of pest insects of deciduous and coniferous trees per year is thus always10.
References
- Moraal, L.G. (1996). 50 jaar monitoring van insectenplagen op bomen en struiken. In bossen, natuurgebieden en wegbeplantingen. Nederlands Bosbouwtijdschrift, (68) 5: 194-203.
- Moraal, L.G. (1999). Insectenplagen op bomen en struiken in 1998 in bossen, natuurgebieden en wegbeplantingen. Nederlands Bosbouwtijdschrift, (71) 3:138-143.
- Moraal, L.G., G.A.J.M. Jagers op Akkerhuis en D.C. van der Werf (2002). Veranderingen in insectenplagen op bomen. Monitoring sinds 1946 maakt trends zichtbaar. Nederlands Bosbouwtijdschrift, (74) 2:29-32.
