A study on sensitivity of overwintering instars to temperature of alfalfa seed chalcids

The alfalfa （Medicago sativa）seeds, harvested at the current year, were stored in 4 locations with different temperatures. The alfalfa seed chalcid (Bruchophagus roddi) overwintering instars and its survival were investigated by dissecting the seeds regularly. The results showed that seed chalcid overwintering instars in alfalfa seeds were the third instar larvae. When the average storage temperature and humidity were 18 ℃ and 27.2% (from October to December), the alfalfa seed chalcid overwintering larvae began to pupate at the end of December. When the average storage temperature and humidity were 9.9 ℃ and 40.1% (from October to next February), the overwintering larvae began to pupate at the next February. Alfalfa seeds being treated with the conditions of 50 ℃ and -30 ℃ for 1 day showed that the mortality of alfalfa seed chalcid larvae reached 100%; and germination rates of the alfalfa seeds were 93.33% and 88.33%, respectively.