Field and Laboratory Observations on the Biology of Aceria angustifoliae with Emphasis on Emergence of Overwintering Mites

SIMPLE SUMMARY: Aceria angustifoliae Denizhan et al. (Acari: Eriophyidae) is the most common mite infesting Russian olive, Elaeagnus angustifolia L. (Elaeagnaceae), in Iran. In the native areas, the fruits of Russian olive are used in folk medicine, and its plants are common in green spaces and parks. This plant is classified as an invasive alien species in North America and A. angustifoliae is considered one of its more promising biological control agents. A study carried out from winter 2017 to spring 2019 clarified some biological aspects of its life strategy by means of field observations (sticky trap bands and direct leaf inspections) and exposing overwintering mites to various constant temperatures in the laboratory; a linear regression of the emergence rates of overwintering mites at constant temperatures was applied in order to calculate the lower developmental threshold. ABSTRACT: Data on the life strategy of A. angustifoliae (population fluctuation in buds and on leaves, emergence and migration to the overwintering sites), as well as its temperature-dependent emergence from overwintering sites at constant temperatures, were determined. The eriophyid mite overwintered into buds and the density of active mites inside them from winter 2017 to spring 2018 was higher than that in winter 2018–spring 2019. In the second half of March 2018 and in winter 2018–spring 2019, the mite density inside the buds decreased gradually with a peak of emergence occurring at the beginning of plant blossoming. Population density on leaves increased in summer, reaching a higher and later peak in 2018, and gradually decreased in autumn with mites migrating to overwintering sites. A lower developmental threshold of 4.5 °C was calculated. About half of the mite population was estimated to emerge from the overwintering sites at an accumulation of degree days ranging, on average, between 85.5 (at 20 °C) and 104.4 (at 10 °C) degree days above the assessed threshold.