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Classification:

Bromius obscurus belongs to the subfamily Eumolpinae, tribe Bromiini.

Distribution:

Palearctic (Europe, Asia, North Africa); introduced to North America.

Habitat:

Light forests, forest edges, tall perennial herb communities.

Description:

Length 5 - 6 mm; body black, short haired; pronotum strongly arched, without lateral margin and densely dotted; elytra black or brown, wider than pronotum, parallel sided with distinctly pronounced shoulders, densely dotted with indicated rows of dots; antennae black with reddish base; middle and hind tibia in front of tip without tooth; claws completely split.

Biology:

The Western Grape Rootworm Bromius obscurus is a parthenogenetic species in Europe. The offspring develop from unfertilized eggs. In North America there are also sexual forms.
The adults of Bromius obscurus appear at the beginning of May and eat holes in the leaves of their host plants. They live mostly on Onagraceae and are often found on willowherbs (Epilobium), but also feed on other plants such as blackberries (Rubus) and grapevines (Vitis). The females start laying eggs after about 2 weeks. These are laid in small groups under bark or in other protected places. The larvae hatch after 8 - 12 days, dig into the soil and feed on the roots of their host plants. Bromius obscurus hibernates as a full-grown larva at greater depths in the soil, perhaps sometimes also as a pupa.

References, further reading, links:

1. Rheinheimer, Joachim, & Hassler, Michael: Die Blattkäfer Baden-Württembergs, 2018, 928 pages, Kleinsteuber Books (Karlsruhe), ISBN 978-3-9818110-2-5
2. Arved Lompe: Die Käfer Europas - Ein Bestimmungswerk im Internet