A COMPARISON OF THE WATER-BALANCE CHARACTERISTICS OF TYPHLODROMUS-OCCIDENTALIS AND AMBLYSEIUS-FINLANDICUS MITES (ACARI, PHYTOSEIIDAE) AND EVIDENCE FOR THE SITE OF WATER-VAPOR UPTAKE

To determine how adult Typhlodromus occidentalis, a mite used in the b iological control of spider mites, thrive in arid western North Americ a, the water balance characteristics of adult females were compared to those of a laboratory colony of Amblyseius finlandicus originating fr om Finnish apple orchards. The mites contained comparable amounts of w ater (73.6 and 74.9%, respectively, for T. occidentalis and A. finland icus), absorbed water from the air between 86% and 92% relative humidi ty (RH) (critical equilibrium humidity) and drank free water from drop lets. Typhlodromus occidentalis were distinguished, however, by having lower net water loss rates (0.8% versus 1.3% h(-1) at 0% RH, 20 degre es C for A. finlandicus), a feature that enables them to retain water more h effectively. Above the critical equilibrium humidity water was lost by adult female T. occidentalis whose mouth parts had been blocke d with wax, implying an oral uptake mechanism for the absorption of wa ter vapour. (C) 1998 Chapman & Hall Ltd.