PestFacts November 2022
European earwigs in canola
Large numbers of European earwigs () (Forficula auricularia) have been reported in the Tumby Bay region. There are concerns about possible contamination in the coming harvest, with the risk of loads being rejected and having to be cleaned, as has happened in previous years.
Earwigs, at this stage of the year, should be eating mostly pest insects such as aphids, rather than (mostly) seedling leaves, so they can be beneficial.
Avoiding grain contamination in broadacre crops
Earwigs are nocturnal and will shelter during the day, making that a better time to harvest. Trials have shown that earwigs are more likely to shelter under swathed (windrowed) than in standing crops. Therefore harvesting during the heat of the day is ideal for both standing and swathed crops as earwigs will remain on the soil surface.
If swaths are harvested during the heat of the day, the number of vagrant earwigs found in the grain is not significantly different to that of a standing crop. When swathing crops, maintain the correct swath height to ensure swaths remain above the ground. If swaths are sitting close to or on the ground, earwigs are more likely to be harvested with the grain, especially if using crop lifters rather than a belt pick up front.
How to report
To help us understand European earwig movement, please report numbers, and any contamination to the PestFacts SA team. We’d also like to know what invertebrates you find in your crops and pastures – whether it is a pest, beneficial, or unknown.
Send your reports or identification requests via the PestFacts map or contact
Rebecca Hamdorf
Phone: 0429 547 413
Email: rebecca.hamdorf@sa.gov.au
Maarten van Helden
Phone: 0481 544 429
Email: maarten.vanhelden@sa.gov.au
More information
Look out for beneficials
A multitude of beneficial predators and parasitoid species prey on crop pests, which can have a significant impact on pest populations. You should only use insecticide when control by natural enemies or other factors is unlikely to prevent economic yield losses. Hence, monitoring should include recording trends in beneficial populations.
Here are some beneficial groups found throughout southeastern Australia:
Parasitic wasps
Several species of female parasitic wasp lay their eggs into aphids or caterpillars. The developing wasp larva either feed inside or from the outside of the host. Aphid ‘mummies’ – bronze-coloured, enlarged aphids – indicate the activity of parasitic wasps. Even with little mummies visible, parasitism can be quite high, simply because the mummy is only the very last stage of wasp development.
Aphid parasitic wasps usually attack just a single pest species. They can only live where and when their hosts occur.
Caterpillars parasitised by wasps often have larvae emerging and pupating around the dead caterpillar.
Ladybird beetles
Found in all crops, larvae and adult ladybirds are voracious aphid predators, and also feed on leafhoppers, thrips, mites, moth eggs and small caterpillars.
Ladybird beetles undergo a significant transformation as they mature. As larvae, they have grey/black elongated bodies with orange markings and may be covered in spines or white fluffy wax material. As adults they are round to oval shaped, with black spots on red, orange or yellow shells. Unfortunately, ladybirds rarely multiply quickly enough to control outbreaks.
Hoverflies
Hoverfly larvae attack a range of soft-bodied insects but prefer aphids. They are common in flowering crops, such as canola, pasture paddocks, and some roadside flowering weeds.
Hoverflies are most noticeable in the adult fly form, when they have dark-coloured flattened bodies with black and yellow markings. But it is the larval ‘grub’ stage (a greenish or cream maggot) that is predatory. As larvae, they are often mistaken for pest caterpillars such as diamondback moth but lack the typical head capsule of caterpillars.
Lacewings
Lacewings are voracious predators and will try to eat almost any insect standing in their path, including aphids, thrips, mites, caterpillars and moth eggs. Both larvae and adult brown lacewings are predatory, while only the larvae of green lacewings are – the adults feed on nectar and pollen following pupation. After sucking the internal contents of their prey, lacewing larvae impale their victim’s exoskeletons on their backs. Brown lacewing larvae can eat 100–200 aphids during their lifetime.
Larvae lack wings and have protruding sickle-shaped mouthparts and a long body shape that varies from thin to stout-like. As adults, they have prominent eyes and long antennae, with large, clear wings with many veins, giving a lacy appearance.
Damsel bug and predatory shield bugs
You will generally find damsel bug and predatory shield bugs in the canopy of crop plants, feeding on a range of soft-bodied prey including small caterpillars, moth eggs and aphids.
Damsel bugs have a slender light-brown body with long antennae and large protruding eyes. They have a long curved ‘snout’ they carry under the body when not feeding.
There are several species of predatory shield bugs that vary in size and shape. Adults have shiny, shield-shaped bodies, often with patterns and spikes. Juveniles are dark red and brown but early instars start out bright red.
Earwigs
You might consider European earwigs to be a pest as they nibble on plants and kill seedlings; but they are also good predators of aphids! In plant later growth stages, they are considered a beneficial insect. You often will find earwigs hiding during the day in the rolled leaves of cereals, and nocturnally consuming aphids . Native earwig species aren’t known to damage seedlings and are clearly a beneficial insect but rarely show high populations in crops.
How many beneficial insects are enough?
Unfortunately, there is no simple answer. Currently, there are no predator:prey ratios that can guide management decisions.
However, there are some helpful guiding principles:
- Most beneficial species are highly mobile and will move from crop to crop if left unsprayed. There is often a lag time between the growth of pest populations and increases in the abundance of beneficials, particularly in the southern cropping systems during spring.
- Sometimes, beneficials will prey on pest species feeding on early crops before attacking other species during later growth stages.
- You should monitor crops regularly so you can measure whether the number of beneficial insects (per sweep, per metre, etc.) is increasing (or not).
- Whenever possible, choose a specific pesticide that does not affect beneficials, instead of a broad-spectrum insecticide. Though it might be more expensive, the overall effect could help avert an increase in pest numbers.
More information on beneficial insects on the GRDC website:
Faba bean aphid movement
The exotic faba bean aphid (FBA, Megoura crassicauda) was originally detected in a suburban backyard in Sydney in October 2016, and then on faba bean crops at Tamworth and Breeza in northern New South Wales in October 2017. It was determined to be infeasible to eradicate.
Very few faba beans were sown in northern NSW during 2018 and 2019. However, , FBA was then detected in Grafton in July 2020. Since 2020, incidences of FBA have increased, with several populations observed in NSW and Queensland. This winter there were outbreaks reported in various parts of NSW including the north west, central west and Riverina. FBA has also been recorded in suburban backyards in Melbourne, but the PestFacts south-eastern team have had no reports of FBA in broadacre crops (see Have you seen the faba bean aphid?).
Biology and potential impact
There is limited information about this aphid in field conditions. Hosts for FBA include Fabaceae (legumes) within the genera Lathyrus and particularly Vicia, which includes
- faba beans
- broad beans
- vetch
The NSW Department of Primary Industries suggests that FBA prefers faba bean and vetches, followed by common pea and lentils. Lucerne, sub clover and legume weeds support limited reproduction of FBA, acting as alternative hosts all year round.
What FBA looks like
FBA are large and can coexist on leguminous plants with the pea aphid () (Acyrthosiphon pisum) and cowpea aphid ()(Aphis craccivora) but are easily identified:
- aphid up to 2.5-3mm in length
- dark green spindle-shaped body with long legs and antennae
- black head, pro-thorax, antennae, leg, siphunculi (`exhaust pipes`) and cauda (`tail`)
- red eyes
- large tubercles (structure at the base of antennae) that face outwards when viewed from above
- slightly swollen siphunculi.
Biosecurity and reporting
So far, growers have not detected this aphid in South Australia but it could spread. Growers and agronomists are encouraged to implement and maintain good on-farm biosecurity measures and be vigilant for unusual pests or disease symptoms in crops.
Report suspect observations immediately to the Exotic Plant Pest Hotline on 1800 084 881.
The latest information for growers and advisors on the activity and management of pests in all broadacre crops during the winter growing season.
