The effects of 20-hydroxyecdysone on breaking diapause of Diprion pini L. (Hym., Diprionidae)

The pine sawfly, Diprion pini L, like almost all Diprionidae, has complex d iapause phenomena which affect the prepupal stages (eonymph and pronymph) i n the cocoon. Experiments using 20-hydroxyecdysone to break diapause of dif ferent populations of D. pini, were conducted. Doses of 2 and 10 mu g/g of the hormone were injected into the insects in diapause, previously removed from their cocoons and placed in transparent capsules to observe their deve lopment. The experiments showed that 20-hydroxyecdysone may cause D. pini t o resume development and may even totally break the diapause. However, this reactivation seemed to require large doses of 20-hydroxyecdysone. Moreover , the effects of applying this hormone varied according to the insect's ori gin, duration of the diapause maintenance and conditions of photoperiod and temperature present before and after the treatment. According to the cases , this resumption of development can affect a variable fraction of individu als and be more or less complete. It is, suggested that the reaction to 20- hydroxyecdysone in standard conditions could be used to measure the intensi ty of the diapause of natural D. pini populations.