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Redlegged earth mite

Halotydeus destructor

Other common names: Red spider mite

Very common and widespread pest of pastures and most broadacre crops. Approximately 1 mm in length with a velvety black body and 8 orange-red coloured legs. Redlegged earth mites are commonly controlled using insecticides, however, non-chemical options are becoming increasingly important due to evidence of resistance and concerns about long-term sustainability.

Redlegged earth mites are one of the most important invertebrate pest species in Australian agriculture. They are common and widespread, and active from autumn to late spring in southern Australia, but not in northern NSW. Redlegged earth mites often occur in situations with other mites, such as blue oat mites, Bryobia mites and Balaustium mites.

The known distribution of redlegged earth mites in Australia (Source: cesar)

Redlegged earth mites are 1 mm in length. Adults and nymphs have a velvety black body with eight orange-red coloured legs. Newly hatched mites are pinkish-orange with six legs and are 0.2 mm long. 

It is important to correctly identify redlegged earth mites because other mite species respond differently to registered pesticides.

Distinguishing characteristics/description of redlegged earth mites (Source: Bellati et al. 2012)

Redlegged earth mites reproduce sexually and can have up to 3 generations per season. In autumn, over-summering eggs hatch when there is significant rainfall and the mean daily temperatures fall below approximately 21°C. The first two generations lay eggs that mostly hatch during winter. It takes approximately 4-6 weeks for nymphs to develop into mature adults. In spring, the third generation of mites produce over-summering eggs that are retained in their bodies. When the female dies these eggs remain on the soil surface and will hatch the following autumn. 

Lifecycle, critical monitoring and management periods for the redlegged earth mite (Source: cesar and QDAFF)

Redlegged earth mites are often found on the leaf surface in feeding aggregations, of up to 30 individuals. In the warmer part of the day, redlegged earth mites tend to gather at the base of plants, sheltering in leaf sheaths and under debris.

Blue oat mites, Balaustium mites and Bryobia mites.

All crops and pastures, with canola, lupins, cereals and legume seedlings the most susceptible to attack. Weeds can also act as alternative hosts, particularly capeweed. 

Feeding causes silvering or white discoloration of leaves and distortion or shriveling in severe infestations. Affected seedlings can die at emergence with high mite populations. Feeding symptoms can be mistaken for frost damage. Redlegged earth mites have been found to be directly responsible for a reduction in pasture palatability.

Redlegged earth mite feeding damage (Source: cesar)

Inspect susceptible pastures and crops from autumn to spring for the presence of mites and evidence of damage. It is important to inspect crops regularly in the first three to five weeks after sowing. Mites are best detected feeding on the leaves in the morning or on overcast days. If mites are not observed on plant material, inspect soil for mites. Be aware of edge effects; mites move in from weeds around paddock edges. An effective way to sample mites is to use a standard petrol-powered garden blower/vacuum machine. A fine sieve or stocking is placed over the end of the suction pipe to trap mites vacuumed from plants and the soil surface. 

The thresholds below are from Miles (1996).

  • Wheat / Barley: 50 mites per 100cm²
  • Canola / Linseed: 10 mites per 100cm²
  • Pulses: 50 mites per 100cm²
  • Establishing annual medic pastures: 20-30 mites per 100cm²

More recently, a threshold for canola of 10 redlegged earth mites per plant at the late cotyledon-1st true leaf stage has been developed (Arthur et al. 2015). 

Management Options:

French Anystis mites can suppress populations in some pastures. Snout mites and other predatory mites are also effective natural enemies. Leaving shelterbelts or refuges between paddocks will help maintain natural enemy populations.

Do not sow susceptible crops (e.g. canola) into pastures or paddocks known to contain high mite numbers. Rotate paddocks with non-preferred crops (e.g. chickpeas). Pre- and post- sowing weed management (particularly broadleaf weeds) is important. Heavy pasture grazing in spring can help to reduce mite numbers the following autumn.

In Western Australia, resistance to synthetic pyrethroid and organophosphate chemicals has been detected. Rotate chemical classes of insecticides. For low-moderate mite populations, insecticide seed dressings are an effective method. Avoid prophylactic sprays; apply insecticides if control is warranted. Pesticides used at or after sowing should be applied within three weeks of the first appearance of mites, before adults commence laying eggs. Insecticides do not kill mite eggs. Border spraying can be an effective way to control mites, as mites will often move in from crop edges and roadside vegetation. Carefully timed spring spraying using TIMERITE® will reduce mite populations the following autumn, but could also exacerbate other mite problems.

In some areas of Western Australia, redlegged earth mites have developed resistance to synthetic pyrethroids and organophosphate insecticides. Resistance is a risk for all southern grains.

This article was compiled by Paul Umina (cesar) and Garry McDonald (cesar). 

Arthur A, Hoffmann A and Umina P. 2015. Challenges in devising economic spray thresholds for a major pest of Australian canola, the redlegged earth mite (Halotydeus destructor). Pest Management Science (in press).

Arthur A, Hoffmann A and Umina P. 2013. Impact of Halotydeus destructor on crop seedlings at different plant developmental stages and levels of moisture stress. Environmental Entomology 45: 998-1012.

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.

Miles M. 1996. Control threshold and sampling recommendations for insect pests of field crops and pastures. Victorian Institute for Dryland Agriculture, Horsham VIC.

Ridsdill-Smith J, Hoffmann A, Mangano P, Gower JM, Pavri C and Umina P. 2008. Review of strategies for control of the redlegged earth mite in Australia. Australian Journal of Experimental Agriculture 48: 1506-1513.

Umina P. 2007. Redlegged earth mite. Victorian Department of Primary Industries. http://www.depi.vic.gov.au/agriculture-and-food/pests-diseases-and-weeds/pest-insects-and-mites/redlegged-earth-mite

Umina P. 2007. Pyrethroid resistance discovered in a major agricultural pest in southern Australia: the redlegged earth mite (Acari: Penthaleidae). Pest Management Science 63: 1185-1190.

Umina PA, Weeks AR, Roberts J, Jenkins S, Mangano P, Lord A and Micic S. 2012. The current status of pesticide resistance in Australian populations of the redlegged earth mite (Halotydeus destructor). Pest Management Science 68: 889-896.

Date

Version

Author

Reviewed By

Mar-2015

1.0

Paul Umina (cesar) and Garry McDonald (cesar)

Alana Govender (cesar) and Bill Kimber (SARDI)

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