| Alder Leaf Beetle (Agelastica alni (Linnaeus, 1758)) |
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Scientific name: Agelastica alni (Linnaeus, 1758) Common name: Alder Leaf Beetle French name: Chrysomèle de l'aulne, Galéruque de l'aulne. Order: Coleoptera Family: Chrysomelidae Wingspan : 6-7 mm. Biotope: On Common Alder (Alnus glutinosusa) and on Grey Alder (Alnus incana), then especially in damp areas where these trees grow. The larvae and the adults feed on Alder leaves. Geographic area: Europe, central Asia, Siberia. Introduced to the United States of America. Observation period : Adults emerge in July. They winter till next spring about May. Females lay the eggs early June, on the under side of leaves. Larvae grow rather fast and go down to a small depth under the soil. Nymphosis often happens less than two weeks after. |
The Alder Leaf Beetle is a small bluish to violet rounded beetle. The elytra are enlarged at the rear. The pronotum is thinner than the elytra and rounded on the lateral sides. It is wider at the back. The antennae and the legs are black. The antennae are very close to each other at the base on the forehead. The abdomen of females ready to lay the eggs can appear on the lateral sides of the elytra. It is a yellow colour. The Alder Leaf Beetle larvae are black and cylindrical. They can make holes in leaves so that the remaining veins look like lace. You can also find Plagiosterna aenea on Alders and there is a possible confusion. Its pronotum shows a different shape from Agelastica alni's one. It is wider at the front and then almost rectangular-shaped when seen from above. The shoulders, on each front corner of the elytra, show a bump (called humeral calus) just following a small depression. Articles 2, 3 et 4 of the antennae show some russet colour. |
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The shape of the pronotum, the shape of the elytra and the colour of the antennae confirm the identification of the species. This adult beetle cohabited with larvae on an Alder growing on the bank of a small stream. |
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Here are larvae of the Alder Leaf Beetle species, at their last development stage, busy making leaf lace. |
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Here are young larvae which were cohabiting with adult beetles. |
André Bon March 2019