Phylum Arthropoda (Arthropods) ➔ Subphylum Hexapoda (Hexapods) ➔ Class Insecta (Insects) ➔ Order Coleoptera (Beetles) ➔ Family Chrysomelidae (Leaf beetles)

Agelastica alni (Linnaeus, 1758)

Blauer Erlenblattkäfer Alder Leaf Beetle

Synonyms:

Chrysomela alni Linnaeus, 1758 [original combination] | Adimonia violacea Laicharting, 1781 | Cryptocephalus violacea Geoffroy, 1762 |

  • Agelastica alni  3011
    Agelastica alni (Linnaeus, 1758)  Blauer Erlenblattkäfer  Alder Leaf Beetle 
    Agelastica alni
    DE, Chemnitz, Zeisigwald; 2008-04-27 13:25:44
    Image number: 3011

    DE, Chemnitz, Zeisigwald
    2008-04-27 13:25:44

  • Agelastica alni  3018
    Agelastica alni (Linnaeus, 1758)  Blauer Erlenblattkäfer  Alder Leaf Beetle 
    Agelastica alni
    DE, Chemnitz, Zeisigwald; 2008-09-27 12:15:43
    Image number: 3018

    DE, Chemnitz, Zeisigwald
    2008-09-27 12:15:43

  • Agelastica alni, mating  3096
    Agelastica alni (Linnaeus, 1758)  Blauer Erlenblattkäfer  Alder Leaf Beetle 
    Agelastica alni, mating
    DE, Chemnitz, Zeisigwald; 2006-05-06 11:00:10
    Image number: 3096
    mating
    DE, Chemnitz, Zeisigwald
    2006-05-06 11:00:10

  • Agelastica alni  3035
    Agelastica alni (Linnaeus, 1758)  Blauer Erlenblattkäfer  Alder Leaf Beetle 
    Agelastica alni
    DE, Chemnitz, Zeisigwald; 2005-04-23 11:41:39
    Image number: 3035

    DE, Chemnitz, Zeisigwald
    2005-04-23 11:41:39

  • Agelastica alni, feeding pattern  3128
    Agelastica alni (Linnaeus, 1758)  Blauer Erlenblattkäfer  Alder Leaf Beetle 
    Agelastica alni, feeding pattern
    DE, Chemnitz; 2003-09-13 12:08:00
    Image number: 3128
    feeding pattern
    DE, Chemnitz
    2003-09-13 12:08:00

  • Agelastica alni, eggs  3409
    Agelastica alni (Linnaeus, 1758)  Blauer Erlenblattkäfer  Alder Leaf Beetle 
    Agelastica alni, eggs
    DE, Chemnitz, Hutholz; 2010-05-16 11:51:09
    Image number: 3409
    eggs
    DE, Chemnitz, Hutholz
    2010-05-16 11:51:09

  • Agelastica alni, larvae  6995
    Agelastica alni (Linnaeus, 1758)  Blauer Erlenblattkäfer  Alder Leaf Beetle 
    Agelastica alni, larvae
    DE, Chemnitz, Stadtpark; 2015-06-02 10:44:45
    Image number: 6995
    larvae
    DE, Chemnitz, Stadtpark
    2015-06-02 10:44:45

  • Agelastica alni, larva  5450
    Agelastica alni (Linnaeus, 1758)  Blauer Erlenblattkäfer  Alder Leaf Beetle 
    Agelastica alni, larva
    DE, Chemnitz, Hutholz; 2012-06-29 10:01:35
    Image number: 5450
    larva
    DE, Chemnitz, Hutholz
    2012-06-29 10:01:35

  • Agelastica alni, pupa  6311
    Agelastica alni (Linnaeus, 1758)  Blauer Erlenblattkäfer  Alder Leaf Beetle 
    Agelastica alni, pupa
    DE, Chemnitz, Markersdorf; 2013-08-20 12:57:50
    Image number: 6311
    pupa
    DE, Chemnitz, Markersdorf
    2013-08-20 12:57:50

  • Agelastica alni, pupa  6312
    Agelastica alni (Linnaeus, 1758)  Blauer Erlenblattkäfer  Alder Leaf Beetle 
    Agelastica alni, pupa
    DE, Chemnitz, Markersdorf; 2013-08-20 13:03:19
    Image number: 6312
    pupa
    DE, Chemnitz, Markersdorf
    2013-08-20 13:03:19

  • Agelastica alni, pupa  6313
    Agelastica alni (Linnaeus, 1758)  Blauer Erlenblattkäfer  Alder Leaf Beetle 
    Agelastica alni, pupa
    DE, Chemnitz, Markersdorf; 2013-08-20 13:04:24
    Image number: 6313
    pupa
    DE, Chemnitz, Markersdorf
    2013-08-20 13:04:24

  • Agelastica alni, pupa  6320
    Agelastica alni (Linnaeus, 1758)  Blauer Erlenblattkäfer  Alder Leaf Beetle 
    Agelastica alni, pupa
    DE, Chemnitz, Markersdorf; 2013-08-26 13:08:09
    Image number: 6320
    pupa
    DE, Chemnitz, Markersdorf
    2013-08-26 13:08:09

  • Agelastica alni  6328
    Agelastica alni (Linnaeus, 1758)  Blauer Erlenblattkäfer  Alder Leaf Beetle 
    Agelastica alni
    DE, Chemnitz, Markersdorf; 2013-08-27 09:06:42
    Image number: 6328

    DE, Chemnitz, Markersdorf
    2013-08-27 09:06:42

  • Agelastica alni  6329
    Agelastica alni (Linnaeus, 1758)  Blauer Erlenblattkäfer  Alder Leaf Beetle 
    Agelastica alni
    DE, Chemnitz, Markersdorf; 2013-08-27 09:10:41
    Image number: 6329

    DE, Chemnitz, Markersdorf
    2013-08-27 09:10:41

  • Agelastica alni  6330
    Agelastica alni (Linnaeus, 1758)  Blauer Erlenblattkäfer  Alder Leaf Beetle 
    Agelastica alni
    DE, Chemnitz, Markersdorf; 2013-08-27 10:25:22
    Image number: 6330

    DE, Chemnitz, Markersdorf
    2013-08-27 10:25:22

  • Agelastica alni  6331
    Agelastica alni (Linnaeus, 1758)  Blauer Erlenblattkäfer  Alder Leaf Beetle 
    Agelastica alni
    DE, Chemnitz, Markersdorf; 2013-08-27 14:29:32
    Image number: 6331

    DE, Chemnitz, Markersdorf
    2013-08-27 14:29:32

  • Agelastica alni  6332
    Agelastica alni (Linnaeus, 1758)  Blauer Erlenblattkäfer  Alder Leaf Beetle 
    Agelastica alni
    DE, Chemnitz, Markersdorf; 2013-08-27 18:19:17
    Image number: 6332

    DE, Chemnitz, Markersdorf
    2013-08-27 18:19:17

  • Agelastica alni  6335
    Agelastica alni (Linnaeus, 1758)  Blauer Erlenblattkäfer  Alder Leaf Beetle 
    Agelastica alni
    DE, Chemnitz, Markersdorf; 2013-08-28 15:27:47
    Image number: 6335

    DE, Chemnitz, Markersdorf
    2013-08-28 15:27:47


Classification:
Agelastica alni belongs to the subfamily Galerucinae.
Distribution:
Europe, parts of Asia, North America.
Habitat:
Water margins, gallery forests - on grey and black alders.
Description:
Agelastica alni is a 6 - 7 mm large, shiny dark blue or blue-violet beetle with finely dotted elytra, which widen significantly towards the hind end. Antennae and legs are black.
The larvae, which are mainly black in the last stage, reach a length of up to 11 mm.
Biology:
The Alder Leaf Beetle Agelastica alni forms one generation per year.
After overwintering, the adult beetles appear from April. They prefer to feed on freshly sprouting grey and black alders. Birches and willows are only visited when there is a lack of food. After maturation feeding and mating, the females start with oviposition from beginning of May. A female lays on average about 200 - 250 (maximum 400) yellow eggs. These are attached in groups of about 60 - 70 eggs to the undersides of the leaves of the host plants. After 10 - 12 days the larvae hatch. These pass through 3 larval stages in 25 - 30 days. The young larvae, which initially live sociably, separate themselves in the last stage. The adult larvae pupate in an elongated cocoon in the ground. The pupal period lasts 21 - 23 days. The duration of the development is strongly influenced by environmental conditions such as temperature and food supply.
The imagines of the new generation normally hatch in August and September. They feed holes in the leaves of their host plants and, in extreme cases, can skeletonize them.
Agelastica alni hibernates as an imago in the moss or foliage layer near host plants.
Natural enemies:
The Alder Leaf Beetle is parasitized by various species of braconid wasps (Braconidae), ichneumon wasps (Ichneumonidae) and some species of tachina flies (Tachinidae).
Note:
The Agelastica alni shown in the pictures from 2013 has pupated in kitchen paper. The orange-yellow pupa changed colour about one day before the beetle hatched. The beetle, which was still light-coloured while hatching, had reached its final blue colour the next day.

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