Abundance and phenology of earth mites (Acari: Penthaleidae) and predatory mites in pesticide-treated and pesticide-free grassland habitats in southern new South Wales, Australia

Abstract

Earth mites (Halotydeus destructor and Penthaleus spp.) and predatory mite (Bdellidae, Anystidae, Erythraeidae, Parasitidae) populations were sampled at six pesticide-free grassland sites and three pesticide-treated, improved pasture sites during autumn-spring 1998 in the Leeton district of southern New South Wales, Australia. Overall, earth mite populations were significantly larger at nonirrigated, pesticide-treated sites (12,366/m2/week) than in nonirrigated, pesticide-free sites (6,212/m2/week). Mean populations at pesticide-free sites remained fairly stable (<8,000/m2/week) until September (spring) when they peaked at 22,434/m2/week. Populations at pesticide-treated sites increased significantly during July-August (winter), peaking at 39,282/m2/week in October. Earth mite population densities reached 100,000/m2/week at a single, irrigated, pesticide-treated pasture site during autumn. Predatory mite populations were significantly larger at pesticide-free sites (176.8/m2/week) than at pesticide-treated sites (81.3/m2/week). There were no clear trends in seasonal abundance of predatory mites. Bdellid mites were the most common predators (58.5%) followed by erythraeids (34.6%), anystids (4.9%) and parasitids (2%). Development and use of more specific insecticides in pastures is suggested as a way of minimizing impacts on earth mite predators and improving biological control.