Bryobia mites

Bronwyn Hunt (Merriwa Pastoral Company) has observed small mites that have been crawling around on concrete paths and indoors on window sills, in Kerang, in the Mallee, Victoria. Bronwyn says this annual behaviour has occurred regularly for the last few years. The mites have been identified as bryobia mites (Bryobia spp.), and it is likely that the mites are moving in from the surrounding lawn. Researcher, Aston Arthur (cesar), says bryobia mite numbers across many parts of Victoria have increased substantially in the last few weeks as weather conditions have become warmer.

Unfortunately, the biology and pest status of bryobia mites is poorly understood. Based on morphology, approximately 100 species within the genus Bryobia have been described, with at least six species recorded in Australia. The number of bryobia species that are agricultural pests within Australia is unknown.

In America, bryobia mites are known to invade homes in large numbers, overrunning floors, walls, drapes, window sills and furniture. If crushed, they leave a reddish stain that is quite noticeable on linens, curtains, walls and woodwork. Their presence can be a nuisance but they do not bite humans or animals, transmit disease, or feed on household furnishings and pantry supplies.

Bryobia mites are an important pest of clovers, canola, wheat and lupins. Often called the ‘clover mite’, bryobia mites are less than 1 mm long with a fawn-orange coloured body and orange legs. In the field they are often misidentified as the redlegged earth mite. Bryobia mites can be distinguished by their long forelegs which are 1.5 times their body length.

Unlike most other earth mite species, bryobia mites are most active in warm conditions in autumn, spring and summer. Over the winter period these mites are generally found in low numbers and are unlikely to be problematic. The feeding damage is characterised by a long trail of whitish-grey spots on the upper side of cotyledons and leaves.

Recent findings indicate bryobia mites are significantly more tolerant to a range of registered chemicals than redlegged earth mites. Past experiences with bryobia mites in Western Australia reveal that alpha-cypermethrin is not effective as a control measure. Therefore, alternative control strategies which do not rely solely on chemical control should be considered.