Off-host survival of Eriophyoidea and remarks on their dispersal modes.

Dispersal of eriophyoid mites is crucial for the successful colonization of new plants. Literature suggests that their long-distance dispersal is through aerial transfer. During dispersal, eriophyoids might be captured in vapor or fine drops of water (perhaps most likely in clouds) where they might be protected against water loss and desiccation, but where they would have no food and be exposed to low temperatures and oxygen concentrations. Considerable resistance of these mites to these stressful environmental conditions is expected and has only partly been confirmed experimentally. The aim of the bioassays conducted here was to assess the survival of five eriophyoid species off their host plants, with poor oxygen availability under two temperature regimes. The bioassays were carried out on live mites dipped into two media used as microenvironments: (1) vaseline oil (used also as control treatment), and (2) water solution of Tween 80 (0.2%) and cycloheximide (50 mg/l). The bioassays were performed at 5 ± 1 and 25 ± 1 °C. The survival of mites was assessed weekly (5 °C) or daily (25 °C) by counting live and active specimens. The following species were subjected to the bioassays: Aceria caulobia (a stem gall mite), Aceria ficus (a vagrant mite), Cecidophyopsis hendersoni (a vagrant mite), Colomerus vitis (protogyne/male population and deutogyne morphs; a leaf gall mite) and Phytoptus avellanae (a bud gall mite). The survival rate of the mites was higher at 5 °C than at 25 °C under both experimental conditions. At 5 °C, the survival of almost all species was higher in the water solution (up to 6-7 weeks) than in vaseline oil (3-5 weeks). Longer survival was found for A. caulobia and P. avellanae (gall-making species) than for C. hendersoni and A. ficus (vagrant species). As expected, the deutogynes of C. vitis survived longer than its protogynes. The current results suggest that individuals of some of the tested species are well suited for withstanding cold, starvation and low oxygen rates, which could be found at higher atmospheric layers, within the clouds, allowing them an effective long-distance dispersal.