Additional tests on the effects of pesticides on cryptic species of blue oat mite (Penthaleus spp.) and the redlegged earth mite (Halotydeus destructor)

Abstract

Earth mites (Halotydeus destructor, Penthaleus spp.) are important pests of crops and pastures in southern Australia during the winter and spring. A recent study showed that control of these mites is complicated by different responses of species to several pesticides, with one cryptic species (Penthaleus falcatus) being particularly tolerant. In this study, earth mites were tested against 4 other chemicals registered for mite control (alpha-cypermethrin, phosmet, chlorpyrifos and lambda-cyhalothrin) in an attempt to identify useful pesticides to counter control failures. Furthermore, an isolated population of an undescribed cryptic Penthaleus species (P. sp. x) from northern New South Wales was tested for its response to 8 pesticides. Species responded differently to all pesticides. Halotydeus destructor was usually the least tolerant species except in the case of phosmet where P. major was the least tolerant species. For alpha-cypermethrin and lambda-cyhalothrin, tolerance of all Penthaleusspecies was similar or higher than that of H. destructor. Penthaleus falcatus had a relatively higher tolerance to phosmet than all other species. The response of P. sp. x (New South Wales) to chlorpyrifos was inconsistent between trials and the response of this species to lambda-cyhalothrin was complex. Penthaleus sp. x (New South Wales) was generally more tolerant than H. destructor but not as tolerant as P. falcatus. The results highlight the fact that mite species need to be identified when considering control options and suggest that effective control recommendations need to be developed for each individual species.