Global Warming: Invasion of New Pests in our Forests

Global Warming: Invasion of New Pests in our Forests

Global warming favours the migration of forest pests from warmer regions into Austria, naturally or through importation. Worldwide trading facilitates the introduction of forest and wood pests from package wood, and further spread occurs due to insufficient phytosanitary control measures.

Due to their competitiveness, new pests may replace indigenous species and achieve greater damage against plants in a new habitat than plants in their native habitat. Unless natural predators or parasites intervene, they could become such an specie endangerment threat towards a host plant.

On the assumption of global warming in Central Europe, the following risk scenarios, in connection with the spread and propagation of forest pests, are likely to occur:

• Global warming accelerates the "natural" invasion of forest pests towards the north. Introduced pests which would not have survived may now be able to spread, and establish themselves.
• Due to insufficient phytosanitary control measures, introduced quarantine pests establish in neighbouring countries, and with the lack of climatic barriers, spread from there into Austria.
• Defoliation by bark beetles would not only be a problem of secondary conifer forests in lowlands but threaten also altitudinal stands.

The following pests are examples of the "natural" spread (range extension) of Mediterranean pests during recent years:

Japanese Oak-Silkmoth (Antheraea yamamai)

This beautiful giant butterfly (Figure 1) can be found on oak in broadleaved forests of south-east Austria (Styria, Burgenland, Carinthia). The pest is indigenous to the Far East (from the Amur region to South China and Japan). It was imported to Europe for silk production and has established a small secondary range in Mediterranean countries some 100 years ago. Host trees in Europe are oak and probably chestnut trees. To this point, the green caterpillars have caused no major damage to oak leaves.

The seed bug Oxycarenus lavaterae on Lime trees

This sub-Mediterranean species from Southern Europe belongs to the seed bugs and sucks on mallow plants. In Austria, they can be found en-masse on Lime tree trunks. The range can be extended due to higher temperature sums. It has been discovered in Burgenland, Styria, Lower Austria and Vienna. The physiological impact on host plants has not yet been studied from these invaded regions.

Pine processionary moth (Thaumetopoea pityocampa)

This moth species is the most important defoliator of pines in the Mediterranean region. In Central Europe it occurs incidentally but does not cause much damage due to unfavourable weather conditions in winter. The spread in southern Tyrol, Slovenia and the Wallis is primarily due to an increase of winter temperature. Maximum frost hardiness is 15°C (on average: +8°C). Larvae need periods with daily temperatures above 9°C and night temperatures above 0°C in order to be able to feed during winter time. Caterpillars hibernate in nests (protection against cold) and migrate in spring in form of a “procession” from the trees and pupate in the soil (Figure 2).

Pupation may last from a few months to four years with the moth hatching in summer, and egg lay occurs at the base of the pine needles. About one month later caterpillars hatch, moult twice and start with the establishment of a winter nest. Like the oak processionary moth, the hairs of this pest contain an urticating toxin especially harmful to humans causing toxic irritant dermatitits. 

Mediterranean Bark beetle Tomicus destruens

This bark beetle species is closely related to the Pine Shoot beetle (T. piniperda). The distinction can made only by experts by means of hair rows between the second and third joint of the antenna lobes. T. destruens is a prevailing species in Mediterranean countries (Spain, southern France, Portugal, Italy). Temperatures and humidity have been limiting factors for spreading.

In Italy it is known as the most endangering pine pest, in Spain it occurs on various pine species, and unlike the Pine Shoot beetle, in dryer regions in particular. A substantial difference to our Bark beetle-species is the main flying season of the beetle occurs in autumn. There are initial reports on occurrence of T. destruens in Croatia, on Aleppo pine as a consequence of the extreme summer drought and heat in 2003.

Asian Long-horned Beetle

Since the beginning of the millennium, various locations were discovered in Europe where stands were infested by two dangerous Asian beetle species (Figure 3) (Anoplophora glabripennis = ALB & A. chinensis = CLB). In these regions, various broadleaved trees were attacked by the quarantine pest in the surroundings of trade companies or nurseries which import packing wood or bonsai plants from China. These beetle species are very well adapted to climatic conditions benefiting from a large number of host trees.

The infestation situation remains especially critical in the 16 provinces of Milan, the infested regions comprising already more than 60 square km. Control measures such as

• felling visibly infested trees,
• digging out and thermally eliminating stumps,
• fixing foils at the basal area in order to hinder the hatching of beetles from roots,
• applying pesticides

need time and effort in order to be successful. 

Due to the proximity of Austria and Switzerland, there is great danger that the beetle will colonize in these countries too. As the pest has been discovered already in 24 different tree and shrub species in Italy, we have to assume that in Europe virtually all broadleaved tree species are potentially endangered.