First Occurrence and Re-description of Aculus epiphyllus (Nalepa) from Fraxinus pennsylvanica in Europe

Aculus epiphyllus (Nalepa, 1892) is reported from green ash in Europe for the first time. Ash rust mite has never been found on green ash, and we therefore re-describe and illustrate the female and male, and describe the nymph. The species was collected from the underside of the leaflets of the introduced ash species, Fraxinus pennsylvanica Marshall (Oleaceae) in Hungary.

Herein we report on our discovery of a species of the genus Aculus Keifer, 1959 found on the under surface of the leaves of Fraxinus pennsylvanica, which is an introduced species of ash from North America. Prior to this paper, no eriophyoid species have been recorded from the foliage of green ash (Amrine and Stasny, 1994;Davis et al., 1982). In Hungary, Korda et al. (2019) have recently described Aceria fraxiniflora from the globular sponge-like galls on the inflorescences and fruits of F. pennsylvanica. Because the description of Aculus epiphyllus given by Nalepa (1894) is incomplete we re-described the female and male and described the nymph, and provide morphometric data for the differences between our examined specimens and the data available from literature.

Materials and Methods
The eriophyoid mite fauna of green ash, Fraxinus pennsylvanica Marshall, was studied from plant samples collected in Balf, Győr-Moson-Sopron county (Western Hungary), in May 2019. The plant material was collected in paper and plastic bags, then returned to the laboratory and examined under a stereo dissecting microscope (Zeiss Stemi 2000-C). After clearing the eriophyoid mites in lactic acid they were mounted in Keifer's F-medium with sorbitol on microscope slides (Keifer, 1975). Specimens were examined with the aid of a research phase contrast compound microscope (Nikon Eclipse E600) equipped with a drawing tube (Nikon Y-IDT). A Zeiss Axio Imager A2 microscope was used for making digital microscopic images on slide mounted specimens. The morphology of Aculus epiphyllus was also investigated with the aid of scanning electron microscope (SEM) (Zeiss EVO 40 XVP) at the Research Centre for Natural Sciences, Hungarian Academy of Sciences, Budapest. Live mites were collected individually with a fine entomological needle from fresh plant parts under a stereomicroscope and placed on the SEM holder without fixation, dehydration and sputter-coating.
The generic classification was made according to Amrine et al. (2003) together with further updating. The terminology and setal notation used in the morphological descriptions follow Lindquist (1996). The number of measured specimens (n) is given in parentheses following the body length. All measurements of mites were made according to Amrine and Manson (1996) and are given in micrometers. Measurements and means are rounded off to the nearest integer. All measurements, unless specified otherwise, are lengths. For females the mean and the ranges, for males and nymphs the data of ten and five specimens are given, respectively.
Host plant -Green ash, Fraxinus pennsylvanica Marshall (fam. Oleaceae). Green ash is the most widespread of the North American ash species, native to eastern and central North America, and an invasive transformer tree species in Hungary living in different plant associations, especially along rivers (Csiszár and Bartha, 2004). Green ash came to Europe in 1780, and around 1802 to Hungary (Csiszár and Bartha, 2004;Korda, 2018). Green ash is a new host plant of A. epiphyllus, and until now the first non-European Fraxinus species, which has been recorded as a host. Relationship to the host -This mite caused no discernible symptoms on the host. The mite was found on the underside of the leaflets, on and close to the midrib and veins. It should be noted that 64% of the adult population was male.
Material examined -The re-described and illustrated female among 4 females and 11 males on slide # 1461a, 2 May 2019, coll. Mr. Márton Korda. Other specimens were collected by Mr. M. Korda in the same locality and time. The 3 slides (### 1461b, 1461c, 1461d with described males and nymphs) were prepared from this material containing 3 females, 5 males and 7 nymphs, and 8 females, 7 males and 7 nymphs, and 2 females, 9 males and 5 nymphs, resp. from the leaves of the same green ash tree. Slides are in the corresponding author's collection and deposited in the National Food Chain Safety Office, Directorate of Plant Protection, Soil Conservation and Agri-environment, Budapest, Hungary.

Discussion
This is the first complete and detailed description of males and nymphs of Aculus epiphyllus. We found different characteristics and morphometric data between the examined specimens and the literature data (Table 1). Except for the length of prodorsal shield and width of female external genitalia, the measurements of the specimens collected from F. pennsylvanica were considerably larger than that of the holotype given by Nalepa (1894) and specimens studied by Farkas (1966). The other European ash leaf-dwelling Table 1 Some different characters of Aculus epiphyllus based on the literature and the examined specimens from green ash Character Aculus epiphyllus holotype from European ash (Nalepa, 1894) Aculus epiphyllus from European ash (Farkas, 1966)  Aculus species, Aculus fraxini (Nalepa) has smooth prodorsal shield (versus shield pattern composed of lines of granules in the re-described Hungarian A. epiphyllus specimens), smooth dorsal annuli (apparently microtuberculate dorsal annuli in the Hungarian A. epiphyllus specimens), the scapular setae sc as long as prodorsal shield (whereas prodorsal shield two times longer than setae sc in the studied female and male population of A. epiphyllus), and causes leaf edge rolling (whereas no damage symptom was caused by A. epiphyllus on F. pennsylvanica) (Nalepa, 1894;Farkas, 1965).