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Earwigs

There are several earwig species, but only the European earwig consistently causes crop damage. In some cases, earwigs damaging seedling canola have been difficult to control.

 

Where have they been reported?

Earwigs (unidentified species) have been reported attacking canola seedlings in the Shepparton and Elmore areas of the Victoria’s Northern Country. The pests were of a particular concern because, in one case at least, they occurred in a paddock that had already been re-sown after extensive millipede damage. The earwigs also appeared to survive sprays of alpha-cypermethrin and chlorpyrifos applied for other pests. Surprisingly, earwigs were still present in one canola paddock where the seed had been treated with fipronil about 4 weeks earlier. In many cases, growers confirmed earwig attack through crop inspections at night. Control difficulties could well be the compounding result of different biological and environmental factors related to earwig behaviour. However, little is understood about the ecology of these pests and how they are impacted by farming practices.

Pest habits and behaviour

European earwigs (Forficulina auricularia) are considered to be the predominant pest earwig species in broadacre crops. European earwigs are an introduced species that appear to be spreading in southern agricultural areas, and problems are often associated with high levels of retained stubble from year to year. They have been known to cause damage to several crop types including canola, cereals and some legumes. European earwigs tend to exist communally and will generally appear more abundant than native earwigs.

European earwigs chew developing seedlings and slow plant development. The typical appearance of damage is shredded cotyledons or leaves and/or irregular holes in leaves (click here to see typical damage). Because of their communal behaviour, the earwigs tend to feed on a front at night, starting at the edge and moving deeper into the crop with time. Their distribution can be patchy and the damage they cause is often scattered. However, they can completely defoliate young seedlings leaving only stems or bare ground in patches.

There are other species of earwigs in broadacre agriculture. Native species include the common brown earwig (Labidura truncata) and the black field earwig (Nala lividipes). The common brown earwig is a beneficial insect that feeds on soft-bodied insects such as caterpillars, lucerne flea and mites, but not plants. The black field earwig is s a minor pest species, occasionally attacking crops.

Our advice

In order to make the most appropriate management decision and accurately assess the risk of attack to emerging crop seedlings, it is important to distinguish the European and native earwig species, all of which may inhabit crops. If earwigs damage is suspected, it is best to search for earwigs at night and look for direct evidence they are feeding on plants. During the day, it is best to search under rocks, stubble residue, wood, or to dig up the soil with a spade.

Control options

Control options for earwigs are limited, however there is some evidence that insecticide seed treatments, such as fipronil, can help crop seedlings withstand attack, particularly within the early emergence window. Cracked grain baits (wheat or sorghum) containing chlorpyrifos and sunflower oil may also be used to control pest earwigs.

Description

European earwigs range from 12-20 mm in length, are smooth and shiny dark brown to black in colour with distinctively pale yellow legs. Click here for images of European earwigs. The common brown earwig can be distinguished by the presence of an orange coloured triangle behind the head on the elytra or ‘wing-case’. The black field earwig is smaller at about 15 mm long, and is shiny black in colour.

 

* Sources of field reports of earwigs

Bruce Larcombe – Agronomist, IK Caldwell (Victorian Northern Country)

Greg Toomey – Agronomist, Landmark (Victorian Northern Country)

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