Megabruchidius dorsalis (Fåhraeus, 1839)

Gradinarov, Denis, 2022, First record of the Asian seed beetle Megabruchidius dorsalis (Fåhraeus, 1839) (Chrysomelidae: Bruchinae) in Bulgaria, ZooNotes 198, pp. 1-4 : 2

Megabruchidius dorsalis (Fåhraeus, 1839)

Material examined: Bulgaria, Sofia, Borisova Gradina Park , 42°41’08.2”N 23°20’00.5”E, 560 m a.s.l., 09.i.2022, 1 ♂, 1 ♀ (emerged between February 1st and 5th); the same locality, 15.i.2022, 1 ♀ (emerged between February 1st and 5th); the same locality and date, 3 ♂♂, 2 ♀♀ (emerged between February 5th and 11th); the same locality and date, 1♂, 2 ♀♀ (emerged between February 11th and 16th); the same locality, 16.i.2022, 2 ♂♂, 2 ♀♀ (emerged between February 5th and 11th); the same locality and date, 1 ♂ (emerged between February 11th and 16th) .

A total of 16 adults (eight males and eight females) were obtained from the collected pods by mid-February. The first three adult specimens were observed emerged from the podson the 5th of February. Мost of the adults (nine specimens) emerged between February 5th and 11th, about three weeks after the pods were collected. Larvae of Bruchinae, most likely belonging to the same species, have been observed in dissected pods immediately after collection in early January ( Fig. 1B ). Megabruchidius dorsalis has a multivoltine life cycle and overwinters as larvae and adults ( Kurota & Shimada 2001). In the present study, no adult beetles were found in the pods in January and adult emergence started two weeks after collecting the pods. The small scale of the research however, does not allow conclusions about the life cycle of the species in the newly occupied area.

Megabruchidius dorsalis differ from M. tonkineus by the absence of a long tooth at the apex of the hind tibia and also in the mainly black elytra (in fully sclerotized specimens) ( Yus Ramos 2009, Korotyaev 2015) ( Fig. 2 ). The morphology of the male genitalia of the examined specimens corresponds to that illustrated by Borowiec (1987) and Yus Ramos (2009) ( Fig. 3 ).

The main host plant of M. dorsalis in Europe - G. triacanthos , is a non-native ornamental species and no immediate threat to natural habitats can be expected after establishment of the new alien beetle species. Moreover, in cases of moderate damage to the seeds of G. triacanthos , M. dorsalis can facilitate their germination ( Horvat & Sajna 2021a).

Figures

Fig. 1. Seed pods of Gleditsia triacanthos on the ground in Borisova Gradina Park, Sofia (A) and larvae of Bruchinae from dissected pod (B). Scale bar (B): 1 mm.

Fig. 2. Adults of Megabruchidius dorsalis, emerged from seed pods of G. triacanthos from Sofia, dorsal and ventral views. A, B: male; C, D: female. Scale bar: 1 mm.

Fig. 3. Male genitalia of Megabruchidius dorsalis, Sofia locality. A: median lobe; B: apex of the median lobe; C: lateral lobes. Scale bars: 1 mm (A); 0.5 mm (B, C).