The mango blossom gall midge, Procontarinia mangiferae, is a multivoltine species that induces galls in inflorescences and leaves of the mango tree, Mangifera indica. In subtropical Reunion Island, populations of P. mangiferae are observed all-year round, but the pattern and the role of dormancy in their life cycle have never been documented. We performed field and laboratory experiments using more than 15,000 larvae. We demonstrated that a larval diapause may affect a part of the midge population, regardless of the season. The total duration of the diapause varied from 6 weeks to more than 1 year. One year of field monitoring showed that the highest incidence of diapause was observed in larvae collected during the summer from mango leaves, where it affected approximately one-third of the individuals. This facultative diapause allows the permanent presence of P. mangiferae in the orchards. By recording diapause duration during 22 weeks under controlled conditions, we showed that high temperatures (26 degrees C) increased diapause duration and extended the range of the dates of diapause emergence, whereas cool temperatures (20 degrees C) shortened diapause duration and shortened the range of the dates of emergence from diapause. A temperature decrease from 26 to 20 degrees C triggered the emergence of diapausing individuals. These mechanisms ensure the synchronization of the emergence of diapausing individuals with the appearance of mango inflorescences, which is also induced by cool winter temperatures.