Tolerance of cryptic species of blue oat mites (Penthaleus spp.) and the redlegged earth mite (Halotydeus destructor) to pesticides

Abstract

Blue oat mites (Penthaleus spp.) and redlegged earth mites (Halotydeus destructor) are major pests of crops and pastures in southern Australia. Management of these mites has been complicated by the recent discovery of 3 cryptic parthenogenic species of Penthaleus, whereas prior research had assumed a single species. The response of the 3 Penthaleus species and H. destructor to commonly used pesticides (omethoate, methidathion, bifenthrin and endosulfan) was compared. Penthaleus falcatus was more tolerant of all pesticides than the other species, whereas H. destructor tended to be the most susceptible. The response of P. major was similar to that of an undescribed cryptic species (Penthaleus sp. x). Mites were sampled from 7 sites where control failures had been reported. Three of these failures were due to P. falcatus despite the fact that this species is relatively uncommon. This suggests that the high tolerance levels of P. falcatus relative to the other species may lead to control problems. Nevertheless, samples of P. falcatus from the control failure sites did not exhibit a higher level of tolerance than those from an unsprayed site. Clones of both P. falcatus and P. major differed in tolerance levels, suggesting some potential for the evolution of increased tolerance levels in mite populations. The results highlight the importance of determining species composition when devising control strategies for mite pest outbreaks.