Emerging pest mites of grains (Balaustium medicagoense and Bryobia sp.) show high levels of tolerance to currently registered pesticides

Balaustium medicagoense and Bryobia sp. (clover or pasture mite) have recently been identified as potential emerging pests of crops and pastures within southern Australia. Recorded damage by these mites has markedly increased in the past decade. There is limited information on the pesticide tolerance of these mites relative to other earth mite pests. This study examined the response of Ba. medicagoense and Bryobia sp., using the redlegged earth mite [Halotydeus destructor (Tucker)] as a comparison, to several currently registered pesticides against earth mites (omethoate, bifenthrin, chlorpyrifos, methidathion and α-cypermethrin). Ba. medicagoense had a much greater level of tolerance to all pesticides tested than H. destructor. Similarly, Bryobia sp. had a higher level of tolerance to bifenthrin, methidathion and α-cypermethrin than H. destructor. However, in the case of omethoate and chlorpyrifos, the tolerance levels were similar for Bryobia sp. and H. destructor. Ba. medicagoense had a higher level of tolerance than Bryobia sp. to the organophosphates tested (omethoate, chlorpyrifos and methidathion), but there was no difference for bifenthrin. We were unable to compare tolerance levels between Ba. medicagoense and Bryobia sp. to α-cypermethrin because of inconsistencies between replicate tests. These emerging pest mite species, therefore, have a high natural tolerance to currently registered pesticides and may prove difficult to control in the field. These findings suggest that other strategies that are not reliant on chemicals should be considered for the control of Ba. medicagoense and Bryobia sp.