Blue Oat Mite

Penthaleus major

Family: Penthaleidae

Order: Acarina

Class - Arachnida (Spiders)

Other Names

Pea Mite.


Body - Pale green turning darker to blue black as it feeds with a red spot (anus) on its back. 1 mm long.
Legs - Adult has 8. Pink to orange.
Nymph has 6
Eggs - Orange or pink.
It looks similar to the Redlegged Earth Mite but is smaller with bluish black body with a red dot and pink to orange legs.


Blue Oat Mite is polyphagous but tend to feed primarily on pasture grasses, cereals and peas.
It is an obligate parthenogen and populations are made up of clones and therefore are unlikely to develop resistance to insecticides. (Parthenogenesis is a form of reproduction where an unfertilised egg develops into new individual.)

Life Cycle:

Active during cool, moist period of year, autumn to spring, and produces drought resistant over summering eggs in spring which remain dormant until following autumn. 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 with the combination of low temperatures (less than 200C) and moisture. They pass through 3-4 stages after hatching before becoming adults (egg to larva, protonymph, deutonymph to adult). Generally 2 to 3 generations occur annually depending on length of growing season. Activity ceases with laying of over summering eggs with the onset of warmer temperatures and the drying of the soil.
They have a peak in numbers in mid winter and a second one in spring.


Origin and History:

They were introduced from Europe and first reported from Victoria in 1934.


They are a major pest in NSW.
Economic infestations are limited by the 190 mm May to October rainfall isohyet. They extend to drier climates and are more tolerant of summer rain than Redlegged Earth Mite and Lucerne Flea.


The Blue Oat mite is mainly a pest of pastures in southern Australia. It also is known to cause damage to a wide range of vegetables, lemons, peanuts, cotton, grasses and small grains. It feeds on the upper surface of leaves using its sharp chelicerae to pierce the surface and consume the plant sap as it is exuded. The leaf tips turn brown and appear scorched. Plants may become stunted, producing little forage or grain and take on a silvery appearance. In pastures the Blue Oat Mite prefers grasses unlike the Redlegged Earth Mite which generally feeds on leguminous species.

Management and Control:

Six organophosphate insecticides are registered for the control of the blue oat mite; chlorpyrifos, methidathion, azinphos-ethyl, dimethoate, omethoate and phosmet
Eggs are not killed by the insecticide, which has resulted in mistaken belief of development of resistance to insecticide with mites having hatched after insecticide application. Season long control can be achieved with two strategic applications of insecticide. Spray after autumn break when egg hatching occurs and prior to those mites reaching maturity and laying more eggs which are insecticide resistant. Later in the season two sprays approximately 2 weeks apart will provide long term control.
Leave shelter belts to encourage natural enemies like Snout Mites.

Related 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.
Penthaleus falcatus is similar and often occurs in association with Penthaleus major and another undescribed Penthaleus species.

Similar Species:



Collated by HerbiGuide. Phone 08 98444064 or for more information.