European earwig

European earwig
Forficula auricularia
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Summary:
The European earwig is native to Europe and has spread to several continents, including Australia. It
is a common species that often occurs in groups, and is known to attack some broadacre crops when
conditions facilitate population build-up. European earwig populations can be suppressed by
reducing retained stubble and supporting the role of beneficial insects. No foliar insecticides are
currently registered for European earwigs in broadacre crops, although registered insecticide seed
dressings will give some control of earwigs in moderate numbers.
Occurrence:
The European earwig is commonly found throughout the cropping regions of New South Wales,
Victoria, Tasmania, South Australia and Western Australia. Although common, they are only
occasional pests of broadacre crops, usually when paddocks provide sufficient refuges to facilitate
population build up and survival.
Description:
The European earwig has a dark and relatively uniform body colour with yellowish shoulders, legs
and pincers. They range in size from 12-24 mm long. They have smooth flat elongated bodies and
may be winged or wingless. Winged earwigs have two sets of wings, a short hardened forewing and
a soft membranous hindwing. They have chewing mouthparts, bead-like antennae and 2 pincers at
the rear of the body. Males have longer curved pincers, whereas females have straight pincers.
Adults and nymphs are of similar appearance, but nymphs are smaller and paler.
Distinguishing characteristics/description of male and female European earwigs (Source: Bellati et al. 2012)
Lifecycle:
Although the lifecycle of European earwigs is completed in one year, multiple generations can occur
during that year. Once mated, adult female European earwigs lay batches of 20 to 80 white oval eggs
in burrows in the topsoil that hatch in two to three weeks. The mother remains with the young for
quite some time after they hatch. Nymphs go through five instars before becoming adults; they
resemble the adults but are smaller, lighter in colour and lack wings. Like all insects, the length of a
lifecycle depends on temperature. For European earwigs, the development from egg to adult takes
nine to ten weeks at 25°C, but takes up to five weeks longer at 15°C.
Lifecycle, critical monitoring and management periods for the European earwig (Source: cesar and QDAFF)
Behaviour:
Both adults and nymphs are nocturnal and shelter in dark places during the day. European earwigs
feed on a wide range of food types such as organic matter, fruits, ornamental plants, vegetables,
flowers, seeds, as well as live and dead insects—including earwigs and caterpillars. This adaptable
insect is able to survive under a variety of environmental conditions.
Female earwigs display maternal care, remaining in the burrow protecting the eggs and nymphs.
Females guard the early instar nymphs initially, but after a couple of moults the young must fend for
themselves or risk being cannibalised.
Though some adults have wings, they rarely fly and are mainly spread to new areas and crops by
human activity. They can be transported in contaminated seed, pot plants, cardboard boxes,
machinery and vehicles. Once introduced, earwigs slowly spread from their original infestation
location to neighbouring properties.
Similar to:
Other earwigs, including native earwigs. They are also somewhat similar to staphylinid (rove)
beetles.
Native earwigs are widespread throughout Australia and they are generally found either individually
or in low numbers under rocks or wood. This contrasts to the European earwig that is more
commonly seen congregating in high numbers. Compared to European earwigs, native earwigs are
omnivorous, eating a wide variety of plant and animal material and they are rarely known as crop
pests. Labidura truncata is a common large native earwig (about 35 mm) that is considered
beneficial because of its preference to feed on caterpillars and other soft bodied invertebrates. It
can be distinguished from European earwigs by an orange triangle behind the head.
A native earwig (Labidura truncata); note the orange triangle on its thorax (Source: cesar)
Compared to European earwigs, native earwigs are rarely known as crop pests and can even be
beneficial insects.
Crops attacked:
Predominantly canola, but will also attack cereals, lupins and some legume crops.
Damage:
Earwigs can both damage emerging crops and also contaminate grain at harvest.
Earwigs feed on leaves and stems at night, often in clusters and can chew plants down to ground
level. They can also feed underground such as on germinating seed. Typical earwig damage appears
as irregular shaped holes in leaves or shredded leaves and leaf tips. This can sometimes resemble
snail damage. In severe infestations, young seedlings can be completely defoliated.
At harvest earwigs can contaminate crop windrows and become contaminants of harvested grain.
They can also chew through canola pods, causing seed development to stop. If earwig numbers are
high, the harvested grain may be rejected or require cleaning, ultimately reducing profits. European
earwigs are often patchily distributed and damage can be scattered within a paddock.
European earwig damage to canola seedling; shredded leaf tips or jagged holes in leaves are typical (Source:
Tim Condon 2014)
Monitoring:
European earwigs are mainly found on heavier soil types and are largely nocturnal.
Typically, damage first appears on the outer edge of a paddock. Monitor crops immediately after
sowing by searching for earwigs at night. During the day, search under rocks, stubble residue, wood,
or dig up the soil with a spade. Refuge traps such as carpet squares, tiles or pot plant bases can be
used to detect earwigs. Alternatively, germinating seed baits can be used immediately following the
autumn break. Soak canola seed in water to initiate germination. Then bury several seeds under 1
cm of soil at each corner of a 5 x 5 m square grid. Immediately after seedling emergence, re-visit the
bait site, dig up the plants and count the number of earwigs present. Repeat this at multiple
locations to obtain an accurate estimate of numbers.
Economic thresholds:
Thresholds for European earwigs are unknown (Bailey 2007). However, for another species, the
black field earwig, control should be considered if more than 50 earwigs are found in 20 germinating
seed baits or if 1 earwig is found in 20 spade samples (Murray 2010).
Management options:
Biological:
Predatory beetles (e.g. carabid beetles, which in high numbers may control earwigs), birds and
lizards will feed on earwigs. Earwigs are also cannibalistic and will predate on themselves.
Cultural:
It is believed European earwig numbers have increased in recent years due to increased stubble
retention, which provides a favourable habitat. Removal of trash is an effective management
strategy. Burning stubble in paddocks known to harbor earwigs has been shown to give satisfactory
control, although this practice can bring about wind erosion. Grazing pasture paddocks to below 1.5t
of dry matter/ha in spring will provide a less suitable habitat and reduce earwig numbers.
Chemical:
There are no foliar insecticides currently registered for European earwigs in broadacre crops,
however, insecticide seed dressings may give some control of earwig numbers. Ensure seed
dressings are registered for use on the particular crop in your state. Cracked wheat or cracked
sorghum bait prepared with chlorpyrifos and sunflower oil, then broadcast onto the infested area is
reported to provide some success against European earwigs (Bellati 2010).
European earwig populations can be suppressed by reducing retained stubble, the use of
insecticide seed dressings and the recognition of beneficial insects.
Acknowledgements:
This article was compiled by Paul Umina (cesar) and Sandra Hangartner (cesar).
References:
Bailey PT. 2007. Pests of field crops and pastures: Identification and Control. CSIRO Publishing, Melbourne, Australia.
Bellati J, Mangano P, Umina P and Henry K. 2012. I SPY. Insects of Southern Australian Broadacre Farming Systems
Identification Manual and Education Resource. Department of Primary Industries and Resources South Australia (PIRSA),
the Department of Agriculture and Food Western Australia (DAFWA) and cesar Pty Ltd.
Cassis, G. (1998) Dermaptera. In: Houston, W.W.K & Wells, A. (eds) Zoological Catalogue of Australia. Vol 23. CSIRO
Publishing. Australia.
Henry K, Bellati J, Umina P and Wurst M. 2008. Crop Insects: the Ute Guide Southern Grain Belt Edition. Government of
South Australia PIRSA and GRDC.
Madge P and Caon G. 1987. European earwig, a historical review. Technical Report No. 115. Department of Agriculture.
South Australia.
Murray D. 2010. Black field earwig. Queensland Government Primary industries and fisheries. Retrieved 27 July, 2011, from
https://www.daf.qld.gov.au/plants/field-crops-and-pastures/broadacre-field-crops/integrated-pest-management/a-zinsect-pest-list/soil-insects/black-field-earwig
Rentz, D.C.F. & Keven, D.K.McE. 1991. Dermaptera (Earwigs). In: Naumann et al. (eds.) Insects of Australia. Melbourne
University Press. Australia
Widmer M, Micic S and Dore T. 2008. European earwigs – pest of crops. Department of Agriculture Western Australia,
Farmnote 322.
Version control:
Date
February 2015
Version
1.0
Compiled by
Paul Umina (cesar) and Sandra
Hangartner (cesar)
Reviewed by
Bill Kimber (SARDI)
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