Pest biology

Cereal leaf beetle larva

Summary

The larva of the cereal leaf beetle is a yellowish brown and slug-like larva of up to 4.5 mm; the larva is almost completely covered with a layer of excreta and therefore looks sticky. The larva nibbles the epidermis off the leaves which makes them frayed with a parchment-like look. Major attacks on the flag leaf are the most important attacks. The larvae should be controlled before they get too large. All cereals can be attacked. Use the control guidelines.

Symptoms

In the spring the cereal leaf beetle nibbles lengthy, narrow holes between the leaf veins. These nibblings are usually unimportant as the beetle only has a modest intake of food and the nibbling takes place on the lower leaves. The larvae nibble the epidermis off the leaves along the leaf nerves which can give these a parchment-like white look. Grasses with little space between the leaf nerves are not attacked due to lack of space for the mouth parts. The larvae are attracted by sunlight and young leaf tissue. Therefore major attacks take place at the top of the plants. Here the leaves are also juicier and therefore more attractive to the larvae. Can be mistaken for: The lengthy leaf nibblings are so characteristic that it is difficult to make mistakes. However, at times the larva can be mistaken for small slugs.

Time of attack

The adult cereal leaf beetle is found from early spring onwards but causes only minor damage. The larva is found in large numbers from May onwards.

Biology

The winter quarters of the beetles are typically tree vegetation in field boundaries and open woodland. At temperatures above 10°C and sufficient light the first cereal leaf beetles appear, but egg laying does not take place until at 19-20°C (hot and dry days). The yellow eggs are laid in May-June either individually or in small clusters, preferably near the leaf base. A female lays 100-300 eggs. The egg stage lasts 8-16 days depending on the weather. When the eggs are hatched at the end of May, the larvae begin nibbling leaves. The larvae live through 4 stages in 12-20 days in May and June whereupon they pupate for 19-26 days. When fully developed larvae lose the excreta on the back, the pupation has begun and the larvae will no longer take nourishment. The pupation is completed in the soil at 2-5 cm depth during June-July. In July-August the new beetles emerge and fly to their winter residence. There is just 1 yearly generation. Climatic requirements: Hot springs and summers are highly favourable for the propagation of cereal leaf beetles because egg production will be high under these conditions.

Control measures

Natural enemies: Ladybirds as well as rove beetles and ground beetles eat cereal leaf beetle eggs, larvae and beetles just as fungal attacks can kill the larvae. Gulls eat a good deal of larvae. Conditions influcencing propagation: A high level of nitrogen promotes the development of cereal leaf beetles. Chemical control: Eggs and small larvae should not be controlled as these are very vulnerable to rain or act as feed for ladybirds when there are no aphids in the fields. Control can often be combined with control of aphids. Large larvae can be difficult to control. Use the control guidelines in Crop Protection Online.

Names and distribution

English: Cereal leaf beetle. Other names: Barley leaf beetle, oat leaf beetle. Systematics: Order Coleoptera (Beetle), Family Chrysomelidae (Leaf beetles). Distribution: The Cereal leaf beetle is found in large parts of Europe, North Africa, West and Central Asia. Adventive to the eastern parts of the USA and Canada. In Denmark Cereal leaf beetles can be found in cornfields every year.

Hosts and importance

Importance: In Denmark the cereal leaf beetle larva is a moderate pest – control can be necessary at times. The nibbling by adult beetles is rarely damaging. However, the larvae can do damage through severe attacks on the flag leaves. Spring barley and oats suffer more damage than winter crops because the development of spring crops better suits the spring and summer development of the larvae. An average of 9 Danish trials in spring barley showed that 0.8 larvae per ear-bearing straw corresponded to 15% nibbling of the flag leaf and resulted in a surplus yield, if controlled, of 2.7 hkg of grain per hectare. Hosts: The Cereal leaf beetle lives as larva and beetle on for example oats, wheat, barley, rye and occasionally maize; among the grasses is perennial ryegrass.

Charactaristics

The common cereal leaf beetle has a long body of 5-6 mm. The forewings are blue, green or – more rarely – black with dots in clearly visible rows. The dorsal plate, femurs and tibia are orange while the head and the tarsi are dark. The length of the antennae is approximately half the length of the body. The larvae are foam-like and up to 4.5 mm. The larvae are often described as ”slug-like” because the back is covered with sticky, yellowish grey excreta. The skin is yellowish and the head darkish brown. The eggs are cylindrical and approx. 1 mm long. The colour is light yellow at laying, but it gradually becomes darker. The eggs are laid individually and usually on the lower half of the leaves.

Names in different languages

Danish :	Kornbladbillens larve
German :	Rothalsiges Getreidehähnchen
English :	Cereal leaf beetle larva
Latin :	Oulema melanopus
Norwegian :	Vanlig kornbladbille
Swedish :	Vanlig sädesbladbagge

Cereal leaf beetle larva with excreta on its back

Cereal leaf beetle larva without excreta on its back

Cereal leaf beetle larva and its nibblings

Adult cereal leaf beetle and its nibblings

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