Adelgids

Fir species can be affected by the presence of insects from the Adelgidae family. These fir pests usually attack more than one plant species. Galls are never produced on the fir, but the insects live free on its needles, shoots, and branches. Injuries are caused by stinging and sucking sap.

Dreyfusia nusslini (migratory silver-fir adelges) or Dreyfusia piceae (silver fir adelges) are such fir pests species. They cause stress to the host, and in case of a severe attack, they determine the decrease of the fir’s resistance to diseases.

Control methods. The application of chemical treatments with contact or systemic insecticides is recommended.

Pissodes piceae – European silver fir weevil

These fir pests attack weakened trees, especially those older than 20 years. It has one generation per year, with an extended flight, from spring to autumn. It overwinters in the cracks of the bark or in the litter, in the adult stage (rarely in the larval stage).

The larvae gnaw irregular galleries up to 60 cm long between bark and wood, oriented in all directions, with a starry appearance. The exit orifices (flight holes) are round. The needles of the affected trees turn red, and resin leaks on the trunk. Attacked trees are often visited by woodpeckers, which consume the larvae.

Control methods. The insect populations are reduced mechanically, by extracting and burning the attacked trees, when the species is in the larval stage (latest in pupal stage). Pheromone-baited and chemically treated trap logs can also be used.

Pityokteines curvidens – silver fir bark beetle

Usually, it is considered a secondary fir pest, which colonizes weakened trees. In the case of mass multiplication, it becomes a primary pest that can cause drought of healthy trees on large areas. 70-80 years old spruce trees are most frequently affected. Other softwoods are rarely attacked.

The silver fir bark beetle has 1-2 generations per year and can have a sister brood. The first flight takes place in April and the second one in June-July. This species overwinters in the adult stage.

Fir pests such as the bark beetle cause damages by gnawing, between bark and wood. The infestation can be recognized by the shape of the mother galleries: like an inverted H, printed on the inside part of the bark. Larvae galleries are arranged perpendicular to the mother gallery. The pupation spot (oval feeding area) is well-imprinted in the wood, at the end of each larva gallery. The attack starts from the top towards the base of the trees, the insect being located on the trunks with thick bark. Damaged trees are recognizable by the yellow color of the needles.

Control methods. Due to its potential for mass multiplication, it is recommended to monitor the beetle population and detect outbreaks in time. Pheromone-baited and chemically treated trap trees and trap logs are used for both monitoring and control. Contact insecticides can be applied before and after the flight.

Cryphalus piceae – small fir bark beetle

This pest attacks fir trees, especially the trunks of young trees and the branches of old trees.

The small fir bark beetle is a monogamous insect that develops 2 generations per year. It overwinters as an adult in the galleries formed in the bark.

The female gnaws an irregular mother gallery in the bark or between the bark and the wood. The eggs are laid in this gallery. After their emergence, the larvae gnaw galleries between the bark and the wood, oriented in all directions. Thus, the attack has a starry shape. Pupation takes place deep in either bark or wood.

Control methods. It is recommended to monitor the insect populations and control their number in case of mass multiplication. Pheromone traps and systemic or contact insecticides can be used.

Choristoneura murinana – European fir budworm

This pest has been reported mainly in old fir forests. In case of mass multiplication, however, it also causes damage to young trees. In the case of fir-spruce mixed stands, this budworm also attacks the spruce.

It has one generation per year and overwinters in the larval stage, in the cracks of the bark, or on the shoots located at the top of the crown. Sometimes it overwinters in the egg stage, on the needles.

In the spring, the larvae enter the buds and feed inside them. After the opening of the buds, they attack the needles. The attack is manifested at the tip and the edge of the crown. Affected shoots bend and dry out. Partially affected needles turn red, then gray. Later, these needles are wrapped in a silky web, serving as larvae nests. The web is enlarged over time, sometimes enveloping the entire crown. Following the attack, the growths become curved, irregular and the top becomes crowded, in the form of a stork’s nest. Due to the strong defoliation, bark beetle attacks are favored, thus accelerating the drying process of the trees.

Control methods. Monitoring is done with sex pheromone traps and light traps. The attack is detected by identifying the attacked, curved, or drought shoots, or by observing the silky larvae nests. Chemical treatments are applied when the larvae emerge. In case of a severe attack, the use of a plane is recommended, because the attack is manifested towards the top of the crown. The use of systemic insecticides is recommended in the larval stage. Contact insecticides are suitable for in-flight control, in June-July.

Zeiraphera rufimitrana – red-headed fir tortricid

It is also known as the ‘red-headed bell moth’, and it is one of the most common pests in fir forests in alpine areas. Sometimes it also attacks spruce but prefers old fir trees. It is often found in association with the European fir budworm.

It has one generation a year, flies in July-August, and overwinters in the egg stage (in the cracks of the bark, on the trunk, or on the branches).

Unlike the European fir budworm (which attacks towards the top), the red-headed fir tortricid attacks the lower half and middle part of the crown. The larvae feed on the needles and buds from the annual shoots. Damaged needles are closely tied with silk threads. In mid-June, pupation takes place in the litter, from where the adults emerge.

Control methods. Monitoring is done with light traps, during the flight. Chemical treatments are performed by plane or from the ground. Systemic insecticides are recommended for the larval stage, and contact insecticides may be used for in-flight control. In the egg or larval stage, insect growth regulators can be applied.

Megastigmus suspectus – fir seed chalcid

It is the largest species of Megastigmus and causes damage by infesting the seeds. Usually, at most 5% of the seed production is damaged.

The insect has one generation per year and overwinters as a fully developed larva, in infested seeds, or in cones.

Larvae attack the fir seeds, consuming their content. The damage is observed only after the emergence of the adults, which leave the seeds through a round (or almost round) exit hole.

Control methods. In order to reduce the number of pests, it is recommended to collect and destroy prematurely fallen cones. The seeds should be inspected carefully before being used in nurseries. Chemical treatments are recommended only in the case of mass multiplication.