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United States Department of Agriculture

Agricultural Research Service

Research Project: EFFECTS OF ATMOSPHERIC HUMIDITY ON EVAPORATION RATES OF PHEROMONE

Location: Application Technology Research Unit

2012 Annual Report


1a.Objectives (from AD-416):
The objective of this study is to determine the effect of ambient humidity and saturation of surrounding air with gaseous pheromone on the evaporation rates of pheromone from standard releasers.


1b.Approach (from AD-416):
Investigation of pheromone evaporation at different relative humidity (RH) conditions will be conducted with a custom-built, experimental system. The system is constructed with a RH control unit, a target holding chamber, a stereoscope with a high definition digital camera, and a load cell unit. The custom-designed RH control unit generates air with a constant RH ranging from 10 to 90%. The target holding chamber is a rectangle box with an internal capacity of 0.56 L and is used to position pheromone releasers. The chamber is completely insulated from the environment and its internal air humidity is controlled by the RH control unit. A small 110V AC axial fan will be used to exhaust the air inside the chamber at different air speeds. The fan also creates a vacuum source to draw the air from the air mixing chamber in the RH control unit through the target holding chamber. The stereoscope is mounted horizontally near the window on the side wall of the chamber to take sequential images of pheromone releaser while the evaporation process is taking place. An imaging program is used to record and save the sequential images in a computer. The images will be used to determine the changes in the liquid level of each pheromone releaser. The load cell unit is mounted inside the chamber and is used to measure the mass of the pheromone releaser. The liquid level and the mass will be measured simultaneously in response to the pheromone evaporation. The variables used for the study of pheromone evaporation will be: constant relative humidity ranging from 10 to 90%, air speed, pheromone releaser weight, pheromone releaser surface area, pheromone concentration, and types of pheromone (molecular weight). Ambient air temperature will be maintained at 25°C for all tests. The vapor pressure will be calculated with a Psychrometric Chart software for different relative humidities at 25°C. Pheromone release rates under varying relative humidity will also be monitored using gas chromatography-mass spectrometry. Pheromones within the headspace of the relative humidity chamber will be passively sampled using solid phase microextraction (SPME) and/or actively sampled under vacuum by pulling volatiles onto an adsorbent trap. Pheromones will subsequently be desorbed and analyzed by briefly holding the SPME fiber in the injection port of a GC-MS. Alternatively, methylene chloride will be used to elute volatiles from the adsorbent traps, which will then be injected via an autosampler onto a GC-MS. These procedures will be invaluable for confirming a correlation between change in dispenser mass and actual pheromone release rates.


3.Progress Report:

A system was developed to determine pheromone evaporation rates under controlled environmental conditions. The system consisted of an environmentally-controlled chamber, a precision balance, an exhaust unit, and a computer data acquisition unit. The environmental chamber was able to precisely control ambient temperature ranging from 5°C to 50° and relative humidity ranging from 5% to 100%. Weight changes of three commonly used pheromones were measured to determine the evaporation rate at each combination of the ambient temperatures of 20, 25, 30, 35 and 40 °C and relative humidities of 30, 50 and 80%. Each sample inside the chamber was tested continuously for seven days with the sampling rate of 15 minutes per weight measurement. This project addresses Objective 2.1 of the parent project: "Determine how water droplets amended with spray additives, relative humidity and the morphological surfaces of leaves affect the droplet evaporation time, spread factor and residual pattern on leaves.


Last Modified: 12/18/2014
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