Balaustium Mite

Balaustium medicagoense

Family: Erythraeidae

Order: Acarina

Names:

Medicagoense refers to Lucerne or Medicago sativa because the mite is often feeds on Lucerne and other legumes.

Description:

Red brown body to 2 mm with 8 orange legs with distinctive foot pads. Larger than similar mites when fully grown but young ones can be misidentified as bryobia mite.
Adult - Looks similar to Redlegged Earth Mite with a grey to reddish body with short hairs and may grow to twice the size. Juveniles have orange to dark red bodies.
Colour - Grey to red with red legs.
Body - Greyish to red. Rounded. Up to 2 mm long. Short stout hairs on the body can be seen with a hand lens.
Wings - None.
Mouthparts - Sucking.
Antennae - None
Legs - Red. 8 on adults, 6 on nymphs.
Head -
Thorax -
Abdomen -
Egg -
Habits -
Caterpillar - The eggs hatch into nymphs that look like small adults but only have 6 legs.

Biology:

They probably reproduce asexually (by thelytokous parthenogenesis).
Glands behind the eyes exude a viscous red fluid which is spread over the body by the body hairs and this provides some protection from predators.
They are generalised feeders consuming eggs and early instars of insects, pollen and plant material.

Life Cycle:

Over-summering eggs hatch after rain. This can be in summer time as they have little temperature dependence. The new nymphs are orange and only have 6 legs. Adults have 8 legs. It takes 5-6 weeks from hatching to the adult stage and their may be several generations per year. They require continuous green plant material to survive.
Generally found from March to December with peak numbers in spring and at least two generations per year.
There are probably 7 developmental stages: egg, pre-larva, protonymph, deutonymph, tritonymph and adult.

Habitats:

They tend to be worst on areas with a history of Capeweed.

Origin and History:

Originates from South Africa and probably introduced to Australia in shipments of hay.
It was first recorded in 1935 on pastures at Werribee, Victoria in 1935 (Halliday 2001).

Distribution:

Widespread. Damage is most often reported in the cooler southern agricultural areas.
Damaging infestations have been reported from Narrogin to Esperance in WA. Eyre peninsula in SA and Central Victoria.
The predicted distribution is expected to cover the Mediterranean climate regions of Australia (Halliday 2001; Arthur et al. 2011).

Damage Symptoms:

Whitening or silvering of leaves.
Bleached and dead tips on cereal leaves.
Canola cotyledons become distorted, cupped and leathery or silvered after attack.
(Micic 2005).

Significance:

Symptoms of damage on plants are usually whitening or silvering of the leaves. Mites suck the sap from young soft tissue. They are rarely a problem on continuously cropped paddocks.
They cause more damage to wheat and lupins than canola and oats (Arthur et al. 2010).

Beneficial:

These mites are often predatory and may help control other mites such as Clover Bryobia Mite.

Detrimental:

Usually found in pasture.
Damaging numbers may occasionally occur in cereals, lupins and canola.

Management and Control:

Control early emerging weeds and grasses in cropping paddocks to reduce the build up of mite numbers and size. In most cases crops will not require spraying unless they are following pasture where significant populations were present. Check weeds (especially Capeweed) for mites and add an insecticide to the pre plant spray if necessary. Check crops soon after emergence and if there are more than 10 mites per plant then spraying could be warranted.
Alpha cypermethrin, cypermethrin and endosulfan at high rates have provided good control.
Fipronil (e.g. Cosmos) and imidacloprid (e.g. Gaucho) as seed dressings sometimes provide enough suppression to prevent yield loss.
Chlorpyrifos, dimethoate, omethoate and phosmet provide little control. Esfenvalerate also appears to provide little control.
They tolerate higher rates of alpha-cypermethrin and bifenthrin than red-legged earth mites.

Thresholds:

Thresholds appear to be around 30-40 mites per seedling for Canola and cereals in good conditions.
Agronomists report 5-15 mites per canola or lupin seedling may be damaging under water stressed conditions.
Current thresholds seem to be around 10 per seedling in canola crops,
20 per seedling in lupin crops and
30 per seedling in cereal crops.

Related Species:

There are about 36 species of Balaustium mite in the world and only one (Balaustium medicagoense) occurs in Australia.
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.

Similar Species:

References:

CSIRO. The Insects of Australia. Melbourne University Press. (1991)

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

Avidov, Z. and Harpaz, I. (1969) Plant Pest of Israel. Israel University Press. P

Micic, S. (2009) Pers Comm.

Micic S, Hoffmann AA, Strickland G, Weeks AR, Bellati J, Henry K, Nash MA, Umina PA (2008). Pests of germinating grain crops in southern Australia: an overview of their biology and management options. Australian Journal of Experimental Agriculture 48, 1560-1573.

Acknowledgments:

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