If you want an internal temperature, such as the temperature inside the corolla tube, a small thermocouple thermometer probe would work. If you want external temperature, the same kind of probe might work, or perhaps an infrared thermometer. I know someone who has used infrared thermometer for caterpillar temperatures.

Thank you for the suggestion.

At the moment I am using a data logger, which people used to measure the leaf temperature so I can use them in time intervals to know the day and night time temperature differences. I want to know the difference between ambient temperature and flower temperature and model them behavioral aspect of plant pollinator interactions.