Revision of the Gonioctena nivosa species-group (Coleoptera, Chrysomelidae, Chrysomelinae) in the Holarctic region, with descriptions of two new species

The Gonioctena nivosa species-group of the genus Gonioctena Chevrolat, 1836 is defined and reviewed. It contains six species including two new to science: Gonioctena gracilicornis (Kraatz, 1879), Gonioctena nivosa (Suffrian, 1851), Gonioctena norvegica (Strand, 1936), Gonioctena springlovae (Bechyně, 1948), Gonioctena amurensis Cho & Borowiec, sp. n. and Gonioctena jani Cho & Borowiec, sp. n. Six new synonyms are proposed: Gonioctena nivosa (= Gonioctena arctica alberta Brown, 1952, syn. n., Phytodecta linnaeana bergrothi Jacobson, 1901, syn. n., Phytodecta linnaeanus var. mutatus Achard, 1924, syn. n., Phytodecta linnaeanus var. simplex Achard, 1924, syn. n. and Phytodecta nivosa var. cedehensis Ronchetti, 1922, syn. n.) and Gonioctena norvegica (= Gonioctena janovskii Medvedev, 1976, syn. n.). Phytodecta flavicornis var. limbatipennis Achard, 1924 and Phytodecta nivosa var. bicolor Heyden, 1883 are removed from synonymy with Gonioctena nivosa (Suffrian, 1851) and are synonymized with Gonioctena flavicornis (Suffrian, 1851). Distribution maps, a key to species, color variation, geographic variation of male genitalia and host plants are provided. Ovoviviparity is newly recorded in Gonioctena gracilicornis and Gonioctena nivosa. Lectotypes are designated for Gonioctena affinis, Gonioctena arctica, Gonioctena linnaeana bergrothi and Gonioctena nivosa.