AN AUTOMATIC THERMOELECTRIC COOLING METHOD AND COMPUTER-BASED RECORDING-SYSTEM FOR SUPERCOOLING POINT STUDIES ON SMALL INVERTEBRATES

An automatic controller is described for use with fluid-cooled thermoelectric assemblies and compatible bipolar controllers in supercooling point studies on small invertebrates [Myzus persicae]. The automatic controller provides constant and repeatable cooling rates in the range of 0.4.degree. to 3.degree. C min-1 from +25.degree. to -50.degree. C; under manual control this range can be extended from < 1.degree.-15.degree. C min-1. The controller includes a range of preset lower-limit temperatures and a reset function to heat the system between experiments to the start temperature (+15.degree. C) in < 2 min. Supercooling points were sensed, observed and recorded by a 12 channel, cold-junction-compensated, thermocouple convertor interfaced to a microcomputer, color monitor and dot-matrix printer. Thermocouples were calibrated against a platinum resistance thermometer to derive polynomial descriptors which were incorporated into a microcomputer program (BASIC, Applesoft) to match thermocouples to .+-. 0.2.degree. C. Each thermocouple was sampled at 3 s intervals to .+-. 0.1.degree. C and temperatures of insect-bearing sensors were plotted against time in distinguishing colors on the monitor, using a 2nd computer program. On completion of an experiment all supercooling points for each thermocouple were printed on the dot-matrix printer; the graphical display could be stored on disk or output to a printer. The computer program can be readily modified to implement individual protocol requirements such as the range of temperatures and related information displayed on the monitor, and the thresholds (time and .degree.C) for the recognition of supercooling points. The thermocouple convertor/microcomputer system could be used with any method of cooling.