New information on the Asian walnut moth Garella musculana (Erschov, 1874) (Insecta: Lepidoptera) spreading in the Rostov Region (South of European Russia)

Introduction

The Asian walnut moth Garella musculana (Erschov, 1874) (Lepidoptera: Noctuoidea:  Nolidae) is one of the most serious pests of fruit and young shoots of walnut (Juglans regia L.) (Yoğurtçu, 2018; Yıldız et al., 2018; Zanolli et al., 2022). It is found in India (Khan et al., 2011), Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan (EPPO, 2023a). Then Europe, this species is known from Bulgaria (Beaumont, 2018), Romania (Bostancı et al., 2021), Turkey (Yıldız et al., 2018), Italy, and Ukraine (Sviridov, 2008; EPPO, 2023a). In the South of European Russia, it was first recorded in the Rostov Region (Romanchuk, Kolesnikov, 2021; EPPO, 2023b): in 2018, only one specimen was collected on a light trap. The host plant of the Asian walnut moth is widely represented in the Rostov Region. In the past, walnuts were grown in forestry nurseries; currently they are often planted in private farmsteads and gardens in the central and northern parts of the region.

The arrival and spreading of a new pest in the Rostov Region raise concerns, since many species of Lepidoptera invaders are already known in the region, which are of great economic importance not only at the regional level, but also on the scale of the European part of Russia (Romanchuk, 2020). Some of them are quarantine pests with limited distribution in Russia, posing a serious phytosanitary risk (Romanchuk et al., 2020). G. musculana itself is included in the A2 list of the European and Mediterranean Plant Protection Organization (EPPO) and is recommended for regulation as a quarantine pest (EPPO, 2023c). Contrary to expectations (Romanchuk, Kolesnikov, 2021), the danger of increasing the number of local populations of the Asian walnut moth for walnut plantings is increasing. Based on the above, the aim of this study is to summarize the data of five years of Garella musculana observations in the Rostov Region.

Materials and Methods

To record the Asian walnut moth, 12 monitoring sites were deployed, located on the Myasnikovsky and Neklinovsky municipal district (Fig. 1, Table 1): 1) «1300 km» Station within the Morskoy Chulek Village boundaries, residential sector (47°17'22.3" N, 39°10'50.2"E); 2) Pyatikhatki Village, residential sector (47°17'49.8"N, 39°13'0.9"E); 3) Morskoy Chulek Village, residential sector (47°17'29.4"N, 39°12'52.2"E); 4) Forbs and steppe balka within the Morskoy Chulek Village boundaries (47°17'22.1"N, 39°12'59.1"E); 5) Forest belt and cultivated fields between the Morskoy Chulek Village and the Sinyavskoye Village (47°16'57.5"N, 39°14'0.5"E); 6) Sinyavskoye Village, residential sector (47°16'34.1", 39°18'50.0"E); 7) North-eastern outskirts of the Sinyavskoye Village, balka of the Donskoy Chulek River (47°16'49.9"N, 39°19'4.6"E); 8) Southern outskirts of the Sinyavskoye Village, terrace (47°16'28.2", 39°18'49.9"E); 9) «Nedvigovka» Educational and Experimental Farm of the Southern Federal University (47°16'18.9"N, 39°19'20.2"E); 10) «Chulekskaya Balka» Protected Landscape (47°17'42.5"N, 39°20'13.1"E); 11) Nedvigovka Village, residential sector (47°16'4.3"N, 39°20'55.9"E); 12) «Kamennaya Balka» Protected Natural Object (47°16'28.0"N, 39°22'23.3"E).

Fig. 1 – The territory of the suspected outbreak of G. musculana in the Rostov Region with indicated monitoring sites (see explanations in the text)

To collect adults, an automatic light trap equipped with a DRV 250 W HWL E40 «Osram» mercury-wolfram lamp was used. To increase the efficiency of accounting, the device was combined with a white reflective screen, from which adults were collected into specialized killing bottle. Collected adults were mounted to dry collection.

Results and Discussion

G. musculana was collected for the first time in the Rostov Region in 2018 (Fig. 2). However, until 2022, no new records: not a single specimen on light traps was collected. Meanwhile, isolated cases of nonspecific damage to walnut branches and fruits in the Nedvigovka Village and its environs were noted. But since not a single caterpillar was found it was not correct to attribute this damage to the Asian walnut moth (especially considering the similarity with the signs of the life activity of Zeuzera pyrina (Linnaeus, 1761)).

Fig. 2 – Recorded damage to Juglans regia at monitoring sites: Nedvigovka Village (a) (photo by R. Romanchuk); «1300 km» Station within the Morskoy Chulek Village boundaries (b) (photo by R. Romanchuk); «Nedvigovka» Educational and Experimental Farm of the Southern Federal University (c) (photo by R. Romanchuk); Southern outskirts of the Sinyavskoye Village (d) (photo by E. Bogaeva); general view of Garella musculana adult collected on 5 May 2018 (the first record) (e) and summer 2022 (f) (photo by N. Elfimova)

Table 1 – The results of G. musculana observations at monitoring sites

Explanations to the table: N – Not detected; * – observation of adults; ** – observation and capture of adults; *** – recording the presence of nonspecific damage; **** – recording the presence of damage and caterpillars of the pest.

Numerous records of G. musculana began in 2022 and continues to nowadays. The reason was the increased activity of the pest after several years of no new records is adult individuals began to fly actively and almost regularly to light traps. Not only nonspecific damage, but also damaged branches and fruits with pest caterpillars inside at monitoring sites began to be observed (Fig. 2).

Five years after the first reliable record, we can conclude that the Asian walnut moth has noticeably increased its numbers. When all types of direct and indirect signs of the pest’s activity were recorded (including an outbreak in the number of adults) at individual monitoring sites (Table 1), the highest activity was noted in 2022 (Fig. 3).

Fig. 3 – Cases of detection of direct and indirect signs of G. musculana life activity

The activity of the Asian walnut moth in the Rostov Region decreased in 2023. One of the reasons could be local fluctuations in weather conditions (cold rainy spring and the first half of summer). Meanwhile, recent years the pest has been found in the Donbass and Krasnodar Krai indicating an expansion of its range, according to reports from social networks and citizen science tools (iNaturalist, 2023).

Conclusion

The presence of G. musculana in the Rostov Region continues to be considered a problem because walnuts are quite widely represented in the region. The observed local population of the pest is in the vicinity of populated areas that have a lot of host plants for the caterpillars. According to previous assumption a single introduction of the pest either with nut seedlings or by nature dispersal from the nearest parts of the range was not excluded (Romanchuk, Kolesnikov, 2021). Now the establishment of the Asian walnut moth in a new territory and the expansion of its range in the south of the European part of Russia can observe. That suggests the pest may soon enter the Republic of Adygea. In addition, G. musculana will obviously expand its range in the Donbass.

Based on the available data, we can preliminarily conclude that G. musculana is increasing its importance for local walnut plantings in the Rostov Region. However, given the fluctuations in pest numbers, further monitoring is required.

Acknowledgements

The author expresses his gratitude to his colleagues E. A. Bogaeva, N. S. Elfimova, O. A. Kladkovaya, E. A. Khachikov, D. P. Kupryushkin, who helped during the research.

References

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Статья поступила в редакцию 16 июня 2024 г.

Поступила после доработки 27 июня 2024 г.

Принята к печати 2 июля 2024 г.

Received  16, June, 2024

Revised  27, June, 2024

Accepted 2, July, 2024