Agricultura! land use modifies ecosystem structure and functioning in natural landscapes. This transformation is the main cause of biodiversity change and loss worldwide, product of agricultural expansion, use of agrochemicals, natural habitats loss and fragmentation, and the introduction of exotic species (). The introduction (either intentional or unintentional) of exotic species in new areas could lead to an imbalance in the stability of the host community biodiversity (). However, not all alien species are invasive ( ), but for those potentially problematic or harmful species, control plans should be considered ().

Syrphidae (hoverflies or flower flies) is one of the most diverse and attractive families of Diptera, with over 6,200 described species worldwide except Antarctica and remote oceanic island (). Most adult flies are beneficial pollinators () and the larval stages exhibit a great diversity of feeding behaviors. In Argentina, the hoverflies are represented by some 170 species (), of which three are exotic: Eristalis taeniops Wiedemann, Eristalis tenax (L.), and Syritta flaviventris MacquartRevista de la Sociedad Entomológica Argentina 80(1): 93-95, 2021

(; ; ). Here, Eumerus strigatus (Fallén) (Syrphinae: Merodontini) is reported for the first time in Argentina, from individuals captured in two sites (distant more than 1,000 km) associated with onion crops.

In the New World, the tribe Merodontini is represented by the genera Alipumilio Shannon, Cepa Thompson & Vockeroth, Nausigaster Williston and the exotic Eumerus Meigen; the two latter are present in Argentina ( ; this study). The larvae are unknown in Cepa (Thompson et al., 2010), but the larvae of Alipumilio and Nausigaster are saprophagous in wet decaying vegetal material (; ^{Mengual & López-García, 2015}). On the other hand, the larvae of some species of Eumerus were reported feeding on living bulbs, tubers, stems, rhizomes, and decaying vegetal tissue (); in particular, E strigatus uses onion (Allium cepa L.), potato (Solanum tuberosum L), and various Narcissus spp. as host larval (; ).

comment that some species of Eumerus have been unintentionally transported by human trade outside their natural ranges and are now causing damage to crops in their new range. They also summarize the situation of the exotic genus Eumerus in the Neotropics, alerting on the expansion of Eumerus obliquus (Fabricius) through Brazil and Paraguay along the last twenty years. At present, in the Neotropics there are four stablished species of Eumerus: E. aurifrons (Wiedemann) in Paraguay (), E. funeralis Meigen in Colombia (), E. obliquus in Brazil (^{Marinoni & Morales, 2007}) and Paraguay (), and E. strigatus in Chile (^{Gerding et al., 1999}) and Argentina (this study).

In Chile, larvae of E strigatus have been reported in five localities (Fig. 1) infesting onion and garlic commercial crop, and causing, in at least two of the sites, 40-42% of bulb losses (^{Gerding et al., 1999}). Here, we report information about this species captured in two agricultural regions in Argentina: Villalonga (province of Buenos Aires; 40°03’ S, 62°29’ W) and Pocito (province of San Juan; 31°39’ S, 68°25’ W) (Fig. 1). In Villalonga, the main crops are onion and lucerne (Medicago sativa L.), while in Pocito there is production of horticultural crops such as onion, pumpkin (Cucurbita spp.) and tomato {Solanum lycopersicum L.), and fruit trees such as olive {Olea europaea L.) and grapevine {Vitis vinifera L.). In both sites, we studied the entomophilous vegetations associated with crops and the assemblages of floral visitors. As a result of four field works, we captured six individuals of E. strigatus (three females and three males). The studied individuals are deposited in the following institutions: Cátedra de Botánica General (FAUBA), Facultad de Agronomía, Universidad de Buenos Aires, Argentina; and Museo Argentino de Ciencias Naturales Bernardino Rivadavia (MACN),

Buenos Aires, Argentina. The map indicating the distributions in Argentina and Chile was constructed using SimpleMappr ().

For the determination at the generic level, key of was used. The genus is easily recognized by vein M strongly biangulate, with an external spur, the crossvein rm apical to middle of the cell dm. For the determination at specific level, we followed. Also, we consulted and) to confirm our results. All our individuals present rounded and completely black scutellum (see Fig. 4 c, 020), abdominal tergites 2-4 with transverse white dusted marking, eyes nearly bare, and the distance from hind ocelli to the posterior margin of the head was less than twice that to the front ocellus (see Fig. 5 f, in); males: eyes holoptic; hind tarsus swollen, without a ventro-basal projection (see Fig. 5 d, in); nor dorsoventrally flattened, nor covered with silver reflecting setae; posterior margin of sternite 4 making a shallow V-shape, coming to a blunt point on each side (without projection) and a narrow, but deep, median cleft (see Fig. ., 2013); and females: tergite 5 without a distinct basolateral ridge.TORRETTA, J.P. et al. Eumerus strigatus in Argentina.

Fig. 1: Geographic distribution of Eumerus strigatus (Fallén) in Argentina and Chile. Black stars: new records; black circles: previous distribution. 

New records

Eumerus strigatus (Fallén)

Material examined. Argentina. New records. Buenos Aires: Villalonga, 1 male, 22-XII-2017, ex Hirschfeldia incana (L.) Lagr.-Foss., J.P. Haedo & H.J. Marrero (FAUBA); 1 female, 1-XII-2018, ex Medicago sativa, J.P. Haedo & H.J. Marrero (FAUBA). San Juan: Pocito, 1 female and 1 male, 23-XI-2018, in white pan trap, M.L. Allasino (MACN); 1 male, 24-XI-2018, in blue pan trap, M.L. Allasino (FAUBA); 1 female, 23-I-2019, in yellow pan trap, M.L. Allasino (FAUBA).

Distribution: Palaearctic region, North America,

Australia, New Zealand, Chile, and Argentina.

Here, we update to four the exotic species of Syrphidae in Argentina. We propose monitoring the presence of this phytophagous hover fly due to its potential risk for important horticultural crop. Moreover, we suggest conducting future studies addressing the spreading of E. strigatus in Argentina. Therefore, we have informed local authorities (Sistema Nacional de Vigilancia y Monitoreo de Plagas) about this study.