Redlegged Earth Mite

Halotydeus destructor

Family: Penthaleidae

Order: Acarina

Class: - Arachnida (Spiders)

Description:

Body - Velvety black. Up to 1 mm.

Legs - Orange-red. Adult has 8. Nymph has 6 legs.

Biology:

Life Cycle:

Active during cool, moist period of year, autumn to spring, and produces drought resistance over-summering eggs in spring which remain dormant until following autumn. There is usually 3-4 generations per year. The over-summering eggs are laid on the underside of leaves or on the soil surface around the host. Dormancy of the eggs is broken by the combination of low temperatures and moisture. At least 6 consecutive cold days with mean temperatures below 20oC are required. The mites grow for 3 to 8 weeks before producing thin walled winter eggs and dying. These eggs have no dormancy and hatch almost immediately and pass through four nymphal stages, each on lasting 1-2 weeks depending on conditions. The first generation takes much longer to mature than the second. An apparent drop in infestation often is reported by farmers in July as the first generation dies and the second is hatching. By August, they have usually quite obvious again. Numbers peak in September to October. In spring thick walled, dormant, over-summering (diapause) eggs are produced. These are resistant to being dried out and survive in the soil until the following autumn. Activity ceases with formation of over-summering eggs. These eggs are often held within the bodies of the females when they die. They can withstand surface temperatures of 70oC. Summer rains with high temperatures kill many eggs.

The reproductive capacity of Redlegged Earth Mite is increased when capeweed is present. They tend to congregate in the flower heads.

Generally, infestations are worse in seasons with a cool showery spring, dry summers and an early break.

Habitats:

Broadleaf and legume pastures and crops.

Origin and History:

South Africa. First recorded in WA from Bunbury in 1917. They are now spread across most of southern Australia.

Distribution:

Most prevalent in southern NSW, SA, Tas, Vic, WA.

The economic limit of their distribution is bound by the 205 mm isohyet for May-October and 225 mm isohyet for December-March rainfall.

Significance:

The Redlegged Earth Mite is mainly a pest of broadleaf species and legumes in pastures in southern Australia. It causes more damage than any other pasture pest. It can completely destroy newly sown pastures. Losses of 10 to 80% of dry matter or seed yield have been reported in established pastures. It also causes damage to a wide range of vegetables and broadleaf crops such as canola, peas and lupins. It feeds on the upper surface of leaves using its sharp chelicerae to pierce the surface and feed on the exuded plant sap. Plants may become stunted, producing little forage or grain and take on a silvery appearance. Grasses and cereals are rarely attacked with economic severity.

They foul the pasture so sheep prefer to graze pasture that is free from Redlegged Earth Mite.

12,000 mites/m2 consume the same energy as 1 dse/ha.

Populations up to 100,000 per square metre have been counted. Populations are usually higher in tall dense pasture. 96,000 mites/m2 were in 6 t d.m./ha and 24,000 mites/m2 in 3 t d.m./ha Clover plus Annual Ryegrass pasture in spring 1319

Susceptibility of seedling species to Redlegged Earth Mite damage.
Species     Susceptibility
Canola (Brassica rapa)   S
Tangier Pea (Lathyrus tingitanus)  S
Ochrus Chickling (Lathyrus ochrus) M
Lathyrus clymenum    M
Common Chickling (Lathyrus sativus) R
Dwarf Chickling (Lathyrus cicera)  R
Yellow Lupin (Lupinus luteus)  S
Narrow leaved Lupin (Lupinus angustifolius)M
White Lupin (Lupinus albus)  R
Atlas Lupin (Lupinus atlanticus)  R
Sandplain Lupin (Lupinus cosentinii) R
Hairy Lupin (Lupinus pilosus)  R
Red-Yellow Pea (Pisum fulvum)  S
Field Peas (Pisum sativum)  S
Pisum sativum sub species sativum, abyssinicum, syriacum, jomardii, and elatius and are all susceptible.
Subterranean Clover (Trifolium subterranean)M
Balansa Clover (Trifolium balansae) S
Common Vetch (Vicia sativa)  S
Woollypod Vetch (Vicia villosa)  M
Narbon Bean (Vicia narbonensis)  M
Purple Vetch (Vicia benghalensis) R
One-flowered Vetch (Vicia articulata) R
Bitter Vetch (Vicia ervilia)   R
R = resistant, M = moderately susceptible and S = susceptible to damage from Redlegged Earth Mite.

From Liu et al 1998 and others.

Management and Control:

Seed may be treated with systemic insecticides to protect seedlings.

Contact insecticides can be used if severe attacks occur as plants emerge.

Systemic insecticides are preferred if more than 60% of plants have emerged. Timing is critical for long term control as the insecticides have little effect on eggs. A single spray in autumn after summer eggs hatch and before winter eggs are laid can provide season long control but is difficult to achieve. Two sprays 2 weeks apart will kill all adults and those hatching after the first spray and is the surest way of achieving long term control.

Spring time applications to dense pastures require higher rates than autumn application to emerging pasture.

Heavy grazing reduces both the numbers and effect of the mites.

In cropping situations endosulfan or Talstar may be used. Both of these products have a residual life long enough to kill young mites hatching after spraying.

The time it takes before 100% Redlegged Earth Mite control was lost for various products is shown below.
InsecticideRate (mL/ha)Effective Life (days)
Endosulfan 1000  28
Endosulfan 500  24
Supracide 1000  21
Lorsban 300  12
Le Mat 150-1000 11
From D. James.

For seed treatment, Le Mat is preferred; for bare earth, Talstar or Endosulfan is preferred; and for post emergence use in pastures Dimethoate is preferred.

Pasture legumes tolerant to Redlegged Earth Mite attack are being bred.

Biological control developed by the CSIRO using the anystis mite is promising.

Eggs are not killed by insecticide which has resulted in mistaken belief of development of resistance to insecticide. Mites observed after spraying are usually those that have recently hatched.

Thresholds:

Cereals
Canola1000 mites/m2
Pulses5000 mites/m2
Sample in the early morning, late afternoon or on cloudy days. Avoid sampling in bright light or after rain. Take 10 samples of 10 cm by 10 cm around the base of the plants and multiply by 10 to get the mites/m2

Insecticide Resistance:

Some populations are tolerant to synthetic pyrethroids (Micic pers. com.).

Biological Control:

There are currently 29 species of predatory mites that attack Redlegged Earth Mite in Australia. Scientists are still looking for more effective biocontrol agents.

Related Species:

Similar Species:

Redlegged Earth Mite (Halotydeus destructor) has a dark or black body with red legs.

Blue Oat Mite (Penthaleus major) has a red spot on its back.

Balaustium Mite (Balaustium medicagoense) has short hairs on their body.

Clover Bryobia Mite (Bryobia praetiosa) has very long front legs.
Bryobia mite have a green brown to lead grey body rather than a dark or black body and have long front legs that are twice as long as any other pair.

Lucerne flea.

References:

1319

Liu, Anyou, T. James Ridsdill-Smith and Tanveer Khan (1998). Pulse vary in their susceptibility to Redlegged Earth Mite. Australian Grain, Western Focus i-ii, August-September, 1998.

WADA. Insects and Allied Pests of Extensive Farming. Department of Agriculture - Western Australia Bulletin No. 4185. p63.

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.