Invasive Populations of the Emerald Ash Borer Agrilus planipennis Fairmaire, 1888 (Coleoptera: Buprestidae) in Saint Petersburg, Russia: A Hitchhiker?

Abstract

The emerald ash borer (EAB), Agrilus planipennis, is an invasive beetle of East Asian origin that has killed millions of ash trees (Fraxinus spp.) in North America and Russia. In September 2020, EAB was detected in Saint Petersburg, a notable event for the metropolitan city. The aim of the present study was to investigate the occurrence and ecology of EAB in Saint Petersburg. The presence of two distinct enclave populations of EAB was revealed, each of which has, most likely, been established through separate events of “hitchhiking” via transport vehicles. Following the invasion, the further spread of EAB in Saint Petersburg was slow and locally restricted, most likely due to climatic factors. This spread by “hitchhiking” suggests that the possibility of the further long-distance geographic spread of EAB in the Baltic Sea region (the EU) is high, both by ground transport (120–130 km distance from EU borders) and ferries that transport cars across the Baltic Sea. In certain cases, the development of EAB on Fraxinus excelsior, based on the stem portion colonized, larval densities, number of galleries, exit holes, viable larvae, and emerged adult beetles, was more successful than in Fraxinus pennsylvanica trees. The observed relatively high sensitivity of F. excelsior to EAB, therefore, casts doubt on the efficacy and benefits of the currently ongoing selection and breeding projects against ash dieback (ADB) disease, which is caused by the fungus Hymenoscyphus fraxineus. Inventory, mapping, and monitoring of surviving F. excelsior trees infested by both ADB and EAB are necessary to acquire genetic resources for work on the strategic long-term restoration of F. excelsior, tackling the probable invasion of EAB to the EU.

Invasion of Emerald Ash Borer Agrilus planipennis and Ash Dieback Pathogen Hymenoscyphus fraxineus in Ukraine—A Concerted Action

“…0.6 and 0.7 larvae/dm 2 , respectively), the numbers of viable EAB larvae in branches collected from attacked F. pennsylvanica (91.4%) were significantly higher than in F. excelsior (76.1%) [23]. Differently, a study from Saint Petersburg (1200 km north) showed that the EAB exhibited a slightly more successful development in F. excelsior than in F. pennsylvanica: larval densities, numbers of larval galleries, exit holes, viable larvae, and emerged adult beetles were slightly higher in F. excelsior than in F. pennsylvanica; larval densities were 0.1-0.5 larvae/dm 2 for F. pennsylvanica and 0.3-0.8 for F. excelsior [8]. Yet, the cited work was conducted in the city environment and consisted of small and fragmented empirical data.…”

“…This is different from the situation observed in populations of the beetle approx. 1200 km north in Saint Petersburg, where, following the invasion, further spread of EAB was slow and locally restricted, likely due to climatic conditions characterized by cool and wet summers and freezing winter temperatures [8]. Preceding studies have shown that the life cycle of EAB in eastern Ukraine fells into two cohorts: (1) a "spring" cohort, comprised of larvae hatching in May to June, which develop to prepupae, overwinter in pupal chambers, and adult beetles emerge in May to June the next year (one-year generation); (2) a "summer" cohort, comprised of larvae that hatch later in the summer and overwinter twice-first winter as larvae and the second as prepupae; the ratio of the cohorts is about 1:1 [21].…”

“…Preceding studies have shown that the life cycle of EAB in eastern Ukraine fells into two cohorts: (1) a "spring" cohort, comprised of larvae hatching in May to June, which develop to prepupae, overwinter in pupal chambers, and adult beetles emerge in May to June the next year (one-year generation); (2) a "summer" cohort, comprised of larvae that hatch later in the summer and overwinter twice-first winter as larvae and the second as prepupae; the ratio of the cohorts is about 1:1 [21]. For comparison, in European Russia, the life cycle of the EAB lasts more than 1 year for most individuals in Moscow [22] and at least 2 years in Saint Petersburg [8].…”

“…Therefore, those over 100 of F. excelsior trees that survived or were not susceptible to attacks by EAB (Table 1) constitute a source of material for further monitoring and eventual propagation, for which the current work represents a starting point. As it was emphasized previously [8], inventory and mapping of surviving ash trees, focusing on European native F. excelsior, affected by both ADB and EAB is necessary to acquire genetic resources for the work on strategic, long-term restoration of devastated areas, thereby tackling a possible invasion of EAB to the EU.…”

“…Railway cars also often serve as means for traveling EAB [7]. Consequently, all this makes the invasion of EAB to the EU highly probable [8]. The possibility therefore cannot be excluded that such situation will also put F. excelsior under the threat of extinction, as American ash species currently are.…”