A field‐scale tracer experiment carried out under natural gradient ground water flow conditions showed that colloids can be highly mobile in a fractured and highly weathered shale saprolite. Four colloidal tracers (0.100 μm fluorescent latex microspheres, bacteriophage strains PRD‐1 and MS‐2, and INA, a dead strain of Pseudemonas syringae), were introduced to a 6.4 m deep well, and concentrations of the tracers were monitored in the source well and in downgradient monitoring wells at distances of 2 to 35 m. All of the colloidal tracers were detected to distances of at least 13.5 m and two of the tracers (microspheres and INA) were detected in all of the downgradient wells. In most wells the colloidal tracers appeared as a “pulse”, with rapid first arrival (corresponding to 5 to 200 m/d transport velocity), one to six days of high concentrations, and then a rapid decline to below the detection limit. The colloids were transported at velocities of up to 500 times faster than solute tracers (He, Ne, and rhodamine‐WT) from previous tests at the site. This is believed to be largely due to greater diffusion of the solutes into the relatively immobile pore water of the fine‐grained matrix between fractures. Peak colloid tracer concentrations in the monitoring wells varied substantially, with the microspheres exhibiting the highest relative concentrations and hence the least retention. Rates of concentration decline with distance also varied, indicating that retention is not a uniform process in this heterogeneous material. Two of the tracers, INA and PRD‐1, reappeared in several monitoring wells one to five months after the initial pulse had passed, and the reappearance generally corresponds with increased seasonal precipitation. This is consistent with subsequent laboratory experiments that showed that colloid retention in these materials is sensitive to factors such as flow rate and ionic strength, both of which are expected to vary with the amount of precipitation.
The supercooling point (SCP) of an insect model, the lady beetle Hippodamia convergens Guérin‐Menéville (Coleoptera, Coccinellidae) was markedly elevated by treatment with aqueous suspensions of the filamentous, ice nucleation active (INA) fungi Fusarium avenaceum and slightly elevated by Fusarium acuminatum. Addition of the surfactant Tween 80 to the fungal suspensions further reduced the supercooling capacity of adult beetles. When used alone the surfactant Triton X‐100 produced a greater SCP elevation than Tween 20 or Tween 80. The emulsifier gum arabic was ineffective in elevating beetle SCPs when applied alone and when added to INA fungal preparations it decreased their efficacy. Aqueous suspensions of both viable sporulating and viable pleomorphic (a permanent, degenerative, nonsporulating cultural state) forms of both fungal species were more effective in elevating the SCP than killed preparations except for the pleomorphic F. acuminatum suspension in which the killed form was slightly more active. Application of INA fungi applied in combination with surfactants may be useful in the development of methods for the biological control of overwintering freeze‐susceptible insect pests by decreasing their capacity to avoid lethal freezing by supercooling.
This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implid, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.
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