Mite (Redlegged earth mite) Halotydeus destructor
Species: H. destructor
Scientific name: Halotydeus destructor
Synonym: Penthaleus destructor
Common name: Redlegged earth mite, Black sand mite, Earth mite, Red-legged earth mite, Redlegged velvet earth mite, Red-legged, RLEM.
Halotydeus destructor is a mite that is species of arachnid native to South Africa, commonly called the Redlegged earth mite (RLEM). It is a major pest of pastures, crops and vegetables, in regions of Australia, South Africa and New Zealand, with cool wet winters and hot dry summers. These mites are active in the cool, wet part of the year, usually between April and November. They were apparently introduced from South Africa in the early 1900s. They have adapted mouthparts that lacerate the leaf tissue so they can suck the fluid out the epidermal cells, this leaves them full of air which gives the damaged areas a characteristic silvery look. This leaf damage leads to the death of seedlings. In southern Australia, these mites cause millions of dollars in annual production loss. In New Zealand, economic losses due to this pest are low except on some vegetable crops such French beans and tomatoes that are grown in isolated areas in Hastings and Napier. In most parts of New Zealand, it is normally too wet and the pastures are too dense for large numbers to build up. Populations build up to pest levels rapidly in areas with 380–500 mm of rainfall annually.
Halotydeus destructor adults are only 1 millimetre long with a 0.6 mm wide, flattish, black velvet body with eight, hairy, red-orange legs. Newly hatched mites are pinkish-orange with six legs and are 0.2 mm long 0.6 mm wide and are not generally visible to the untrained eye.
Halotydeus destructor is essentially a soil mite, spending 90% of its time on or near the soil surface and moving up onto plants only to feed. Other mites are attracted to volatiles released from the leaves damaged a feeding mite and so they usually feed in aggregations.
Reproduction occurs when the male, which is smaller than the female produces webbing, usually on the surface of the soil. It then deposits spermatophores on the threads of this webbing, which the female mite picks up and fertilises her eggs. There are usually 3 generations per season with the last generation producing extra thick-walled eggs in spring. These thick-walled eggs go into diapause during the hot summer months. Outbreaks of mites occur after the autumn rains, coinciding with crop or pasture emergence.
A predatory mite (Anystis wallacei) has been introduced in Australia as a means of biological control, however, it has slow dispersal and establishment rates. Although locally successful, the benefits of this mite are yet to be demonstrated.
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