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Further vernacular names:

Brassy Willow Beetle

Classification:

Phratora vitellinae belongs to the subfamily Chrysomelinae, tribe Chrysomelini.

Distribution:

Temperate Palearctic (except North Africa), North America.

Habitat:

In damp forests on willows and poplars.

Description:

Length 3.5 - 5 mm; metallic bronze, coppery or bluish, rarely black; elytra punctured, less regularly on sides; shoulder bulges weak; sides of pronotum behind often parallel or slightly retracted in front of base, but mostly slightly narrowed from base to front; forehead flat or only weakly pressed in with a small dimple in the middle of the front-edge; antennae of the males do not reach the middle of the body, of the females still shorter; 2nd antennal segment shorter than 3rd, the following without hair-tufts; tibiae dark; segment 1 of tarsi of the males clearly more narrowly than the 3.; the base part of the claws is broader and has a pointed tooth; the female's 1st segment of the posterior tarsi is at most 1.5 times as long as the 2nd, the male's 1st segment is usually much narrower than the 3rd segment.
There are some similar species.

Biology:

Phratora vitellinae lives on willows (Salix) and poplars (Populus). Willow species with a high concentration of phenyl glycosides and with hairless leaf underside are preferred.
From April, in cooler locations from May, when the forage plants have developed their leaves, the well flying adults of the Brassy Willow Leaf Beetle Phratora vitellinae emerge from their winter shelter. They mate immediately after hibernation without maturation feeding. A female can lay about 200 - 400 eggs. These are laid in clutches of 12 - 20 eggs on the undersides of the leaves of the host plants. Some days later, the larvae hatch. The larvae live closely together in groups during their entire development and feed together. They pass through 3 larval stages in a maximum of 3 weeks, fall to the ground and pupate. After 10 - 12 days, the new beetle generation hatches and first carries out a maturation feeding.
Phratora vitellinae forms up to 3 overlapping generations per year. The species hibernates as adult beetle under bark.

Natural enemies:

The braconid wasp Perilitus brevicollis (Haliday, 1835) [Hymenoptera, Braconidae] parasitizes the adults of Phratora vitellinae.
The ichneumonid wasp Mesochorus phyllodectae Schwenke, 1999 [Hymenoptera, Ichneumonidae].
The tachinid Medina separata (Meigen, 1824) [Diptera, Tachinidae].

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