In summer 2019, the presence of a quarantine invasive species - the emerald ash borer (Agrilus planipennis) - was confirmed in Ukraine. The pest was found in plantations of the Starokozhivske tract in Markivske Forestry of SE "Bilovodske LMH" (Luhansk Regional Forestry Management) and adjacent forest belts of the Heraskivska village council in Markivskyi district, Luhansk region. Considering that outbreaks of the emerald ash borer caused the death of over 20 million ash trees in Michigan (USA) and Ontario (Canada) in the early 2000s, and have spread from Moscow to Volgograd and Voronezh in Russia, immediate measures must be taken to prevent the spread of this pest in Ukraine.

The emerald ash borer (EAB) is an invasive species. Its natural habitat includes deciduous forests of the Korean Peninsula, northeastern China, Japan, Mongolia, Taiwan, and the Primorsky and Khabarovsk regions of Russia. There it inhabits many species of ash and walnut. Besides green ash (Fraxinus pennsylvanica), the borer also infests European ash (Fraxinus excelsior).

In the mid-90s of the last century, the borer came from Southeast Asia to the USA and Canada, where outbreaks of its mass reproduction and death of ash trees were recorded in 2002. Around the same time, EAB appeared in Moscow's green plantations, with the first official reports appearing in 2003. By 2019, the pest had spread to the following regions of Russia: Bryansk, Kaluga, Lipetsk, Moscow, Orel, Ryazan, Smolensk, Tambov, Tula, Tver, Volgograd, Vladimir, Voronezh, and Yaroslavl regions.

According to experts from international organizations, the EAB range will expand significantly in the coming years. Since its natural spread rate does not exceed 10 km per year, such rapid distribution over vast territories can mainly be explained by human activity (transportation of infested wood and planting material).

EAB belongs to the group of particularly harmful and aggressive stem insects capable of infesting living, usually weakened trees, which inevitably causes their death. Typically, it colonizes from the top and skeletal branches of ash crowns growing in open areas or forest edges. EAB infects trees of various ages in urban plantations of various types (avenue plantings, squares, boulevards, parks) and field-protective forest belts. There is a danger of further spread of EAB to plantations where ash is the main or accompanying species.

EAB is a dangerous quarantine species. The particular danger of its spread beyond the primary range is that in new conditions there are no specialized enemies capable of controlling the population size. EAB larvae are most often extracted from under the bark by insectivorous birds, mainly woodpeckers. The most active birds are at the end of the growing season.

Drying of trees infested with EAB begins from the top and gradually spreads downward. Water shoots appear on trunks, and root shoots appear in the root collar area. With high infestation density, tree death occurs in the second year. Beetles that developed in those trees colonize other trees, forming chronic foci. On large ash trees, the emerald ash borer develops over several years and causes gradual weakening and subsequent death of trees.

Year 1 of infestation - diagnosing EAB presence is quite difficult. The first signs of infestation may be bark pecking by birds and the presence of larval tunnels under the bark.

Year 2 of infestation - characteristic D-shaped exit holes appear on trunks and branches the year after trees are colonized by the borer. Infested trees usually have thinning crowns, discolored leaves, and swellings, cracks, and necrosis on branches and thin trunks. Secondary shoots develop along the trunk and in the root collar area.

Year 3 of infestation - crowns are significantly thinned, dieback of many branches is noticeable, and numerous D-shaped exit holes are visible on the trunk and branches.

During our survey of EAB foci in Luhansk region, larvae of various ages were found on trunks from the root collar to the top, mainly on the south side of the trunk, as well as on branches, with a density of 1 to 3 specimens per 1 dm². The presence of larvae in pupal chambers embedded in the wood indicates that plantations were infested by this pest in 2018-2019. In EAB breeding grounds, ash trees are dying en masse. There is a danger of the dangerous pest spreading to neighboring Donetsk and Kharkiv regions, and then to Sumy region, where quite a lot of ash trees in forest plantations are weakened by chalara necrosis and root rots.

To prevent this, it is necessary to implement a set of measures, preferably before the beginning of sap flow and resumption of larval development after wintering:

- Intensive forest pathological survey of deciduous plantations to clarify the boundaries of EAB spread with the involvement of entomologists from the Forest Protection Laboratory of UkrNDILGA and specialists from SE "Kharkivlisozakhyst";

- Immediate (before beetle flight begins) removal by sanitary cuttings of all infested green ash trees in detected foci with subsequent burning of branches and trunks of cut trees;

- Simultaneously with cutting infested trees, remove stumps or lower them to ground level;

- Strengthen control over the import of planting material, unpeeled wood, wood chips, firewood, etc. into the region;

- Prohibit transportation of untreated wood (without bark removal) beyond the 20-kilometer quarantine zone.

Measures can be considered effective when the following condition is met: no reports of the pest for two of its life cycles and at least three years of annual monitoring in the quarantine area.

How to recognize EAB?

Larvae of various ages overwinter in the thickness of bark or in surface layers of wood in specially prepared cradles. The depth of the cradle reaches 3 mm, length and width - 16 and 3.5 mm respectively. Larvae withstand winter air temperatures down to -30°C. After the beginning of tree sap flow (approximately after air temperature exceeds 5°C), larvae resume development. Younger ones feed and expand tunnels, while older ones soon pupate. The length of older larvae reaches 26-32 mm.

Since larvae of different ages overwinter, they pupate non-simultaneously, and adults emerge similarly non-simultaneously. The first pupae appear in late April at the end of larval tunnels at a distance of 5-10 mm from the bark surface. Young beetles remain in the pupal cradle for 8-15 days, after which they gnaw D-shaped exit holes (average size 3.5×4.1 mm) and emerge outside. The average density of exit holes is 1.4 pcs./sq. dm (from 1 to 2.4 pcs./sq. dm).

The body of the emerald ash borer is emerald green, in places with golden, bronze or purple sheen. The elytra are quite narrow. The beetle length is 8-14 mm. Males live 2 weeks, females - 3 weeks. Beetles are active from mid-May to September. The flight is prolonged. After emergence, adult EAB feed additionally on ash leaves, gnawing small irregularly shaped holes in them. Beetles are active during the day, hiding in bark cracks or in the crown at night.

Female emerald ash borers lay singly from 60 to 90 eggs on the surface of trunk bark or the lower part of skeletal branches. After hatching, the larvae burrow under the bark and gnaw tunnels where they feed on phloem and later on wood during the growing season. At low population densities, larval tunnels are longitudinal or vertical; at high densities - spiral transverse. Vertical tunnels most often have a characteristic upward bend in the end part.

The EAB generation is one- to two-year depending on weather conditions of the region and microclimate of its individual development sites.

Since EAB is a quarantine object, the procedure for its official control is prescribed in the international rules of the European and Mediterranean Plant Protection Organization (EPPO) (BULLETIN OEPP/EPPO BULLETIN (2013) 43 (3), 499-509, STANDARD EPPO PM 9/14 (1).

Stage 1 - conduct a detailed survey of at least a 1 km radius area from the infested tree, including inspections of trunks and branches of trees to identify D-shaped exit holes, signs of bark pecking by woodpeckers and presence of larval tunnels. Based on survey results, obtain a preliminary assessment of the age and spread of the borer in the region. Establish a quarantine zone with a radius of at least 20 km around the first detected infested tree to prevent movement of infested material (including wood, firewood and planting material) and spread of EAB. The radius may be adjusted depending on ash distribution.

Stage 2 - survey to determine boundaries within a radius of at least 1 km around each new EAB-infested tree to obtain preliminary information about the spread zone boundaries. The survey must be conducted immediately after the first detection of the pest.

Stage 3 - the process specified in the first two stages must be conducted until all EAB-infested ash trees are identified.

Stage 4 - all ash trees showing signs of EAB infestation should be cut down within a radius of at least 100 m from each detected infested tree. Each felled tree should be carefully examined (with removal of bark from trunks and branches with diameter from 1 cm) for presence of EAB. Such inspection should continue until an UNINFESTED ash tree is found.

Stage 5 - all ash trees should be combined into an "EAB-infested zone". All ash trees in this zone must be cut down and carefully examined for presence of emerald ash borer.

The described inspection procedure should then be repeated from each new ash tree where signs of EAB infestation are detected.

Yuriy Skrylnyk,
Senior Researcher at the Forest Protection Laboratory of UkrNDILGA, Ph.D. in Agricultural Sciences

Tetiana Kucherevanko,
Head of the Monitoring Department at SE "Kharkivlisozakhyst"

The article was published in "Forestry and Hunting Journal", 2020. No.2. 20-22.
(Skrylnyk Yu., Kucherevanko T. Ash plantations under threat (a new scourge for Ukrainian forests - emerald ash borer)).