Alder leaves eaten down to skeleton of veins in places
Photo Arne Ader
Translation Liis
Alder leaf beetle
Alder leaf beetle Lepapoi Agelastica alni
Melasoma leaf beetle Hundpoi Melasoma aeneum
Larger animals are not particularly interested in alders but smaller creatures run around on them since May, when the alder leaf beetle adults (or imagos) emerged from their winter quarters. Eggs were laid on the undersides of alder leaves, and the hatched larva ate the alder leaves to resemble lace; seen from a distance the leaves look brown. Now alder leaf beetle imagos again clamber around on the trees: they go into winter quarters in order to start a new year cycle in spring. Damage is noticeable in southern Estonia, elsewhere only locally.
The Coccinellidae or ladybird family whom the colourful leaf beetles remind of in shape are beloved by all, but actually predators who destroy plant pests such as aphids. By contrast the leaf beetles are herbivores and pests who can cause much damage, chewing leaves down to a skeleton of veins. The most ”famous” leaf beetle is the Colorado potato beetle (Leptinotarsa decemlineata).
Leaf beetles have more oblong bodies than the “hemispherical” ones of ladybirds. Legs and antenna are a little longer than those of the ladybirds and the belly of leaf beetles is convex. The alder leaf beetle is metallic blue in colour and the most widely spread. The greenish Melasoma aeneum leaf beetle is not so common; its colour can sometimes be blue-tinged.
Leaf beetles crawl fearlessly around on plants as do the colourful ladybirds. Birds know that it is not worthwhile to touch insects with bright warning colours because they secrete toxic liquids – thus the fearlessness of the leaf beetles. Leaf beetle larvae should not be taken up even for study in summer –they have special glands that produce a foul-smelling yellowish liquid for defence, containing prussic acid that causes irritation even on the skin of humans.
The other protective mechanism of leaf beetles is to let themselves drop down from the plants: in case of danger they simply retract antenna and feet under the body and let themselves drop from the tree to the ground.
Damage from their activities is only occasionally as noticeable as this year.
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