green shield bug - photograph copyright Tim Sandall When fully grown the common green shield bug (Palomena prasina) is a broad, flattened, green insect with a darker area at the rear end (see picture). The adult bugs are 10mm long and are often seen basking in the sun in late summer on a wide variety of plants. This insect is native to Britain and is of widespread occurrence, especially in southern England.
The name shield bug is due to the shield shape of the adult insects when seen from above. The immature nymphs have a more rounded shape and are pale green, with some black markings during the earlier instars.
In 2003, another species of shield bug, the southern green shield bug (Nezara viridula) was found for the first time breeding in the London area. This recent arrival from elsewhere in Europe is slightly larger than the native green shield bug. The adults are uniformly green and lack the dark area at the rear end of the body. Immature southern green shield bugs are greenish black with many white, yellow or red circular markings on their upper surface. This species can cause damage to some vegetables, especially runner and French beans, but it remains to be seen whether it will become established to the extent that it becomes a pest. The evidence so far is that this insect does not become numerous until late summer or early autumn, by which time beans are coming to the end of their cropping period.
Although sometimes mistaken for beetles, shield bugs belong to a different group of insects, the Hemiptera. They feed by sucking sap from a wide range of plants but generally cause no noticeable damage to cultivated plants, even when numerous. They overwinter as adults but before seeking sheltered places they are seen in late summer and autumn sitting on plant foliage in the sun. They are also active in early summer when they lay small clusters of eggs on the undersides of leaves.
In recent years the native green shield bugs seem to have become more abundant and widespread. Other species of shield bugs that are brown or yellowish green with reddish markings can also be found in gardens.
Control
The native common green shield bug is harmless, so control measures are not required. If the southern green shield bug becomes a problem it may be necessary to spray with bifenthrin (Bayer Sprayday Greenfly Killer Plus, Scotts Bug Clear Gun, Doff All in One Garden Garden Killer), but check the instructions to make sure that the type of edible plant you are spraying can be treated with this pesticide.
