Metcalfa pruinosa Say, 1830 as a new parasite of hop plants in Ukraine

Abstract

Metcalfa pruinosa (Say, 1830) is an invasive, gregarious sap-sucking insect that spreads rapidly through Ukraine and now detects in Kyiv city, the Autonomous Republic of Crimea, Donetsk, Dnipropetrovsk, Zakarpattia, Odesa, Kharkiv, and Kyiv regions. Additionally, this sap-sucking insect parasitizes more than 300 species of plants, including the common hop (Humulus lupulus L.). H. lupulus is a valuable industrial crop grown in many countries, including Ukraine. In Ukraine, this industrial crop is grown in the Lviv, Rivne, Khmelnytskyi, and Zhytomyr regions. Specifically, the Zhytomyr region accounts for almost 74% of the total area of hop plantations in Ukraine. Thus, hop-growing areas in Ukraine are closest to Kyiv city and the Kyiv region, among the M. pruinosa infested areas in Ukraine. Additionally, H. lupulus is an important ornamental plant used for vertical gardening throughout Ukraine, including Kyiv city. Given the above, this study aimed to characterize the “M. pruinosa — H. Lupulus” host-parasite system in Kyiv city. To achieve the above purpose, the authors visually inspected hop plants in Kyiv city in 2021–2022. As a result, the inspections revealed that infestation of H. lupulus by this parasite predisposed the appearance of sooty mould. The authors also identified that micromycetes belonging to the genus Cladosporium Link, 1816 caused the sooty mould and that these micromycetes used honeydew excreted by M. pruinosa as substrate. Additionally, inspections found that in Kyiv city in 2021 and 2022, 4.4% and 1.29%, and 26.4% and 1.94% of common hop plants were damaged by M. pruinosa and sooty mould, respectively. Finally, the authors described the signs of hop infestation with M. pruinosa and sooty mould-causing micromycetes, including the diagnostic ones. The diagnostic sign of hop infestation by M. pruinosa was, respectively, the presence of a whitish, sticky, woolly coating on the leaves and stems, presented from the beginning of July until the end of October. The non-diagnostic signs of hop infestation by M. pruinosa included interveinal chlorosis and necrosis, chlorotic and necrotic spots on leaves. Meanwhile, the diagnostic sign of sooty mould was the presence of a black sticky coating on the leaves.