Technical Abstract: Quarantine heat treatments, including hot-water immersion, vapor heat, and forced hot air, are used to prevent the spread of exotic fruit flies through marketing channels. Treating fruits infested with eggs, first instars, second instars, or third instars for multiple fruit fly species to develop treatment parameters that provide quarantine security is an expensive, labor intensive, and lengthy process. To reduce costs and accelerate the development of new heat treatments, only the most heat-tolerant fruit fly species and life stage(s) are subjected to 'in situ' bioassay against selected time and temperature parameters of the candidate heat treatment. Presently, three methods are used to determine the most heat-tolerant fruit fly species and life stages: static-temperature water bath, transient-temperature water bath, or, most recently, a heating block system. Shown are the three systems with discussions on their use and efficacy.