title: Effect of temperature and photoperiod on diapause development in a Douglas fir seed chalcid, Megastigmus spermotrophus.
abstract: Douglas fir seeds infested by diapausing larvae of a chalcid, Megastigmus spermotrophus, were transferred under different temperature and photoperiod regimes at various dates during autumn and winter. Both winter diapause and prolonged diapause were compared to the diapause patterns observed in control lots kept under natural conditions. The results showed that exposure to low temperatures in autumn and winter is required for the completion of diapause development. Median adult emergence dates and the date of transfer of larvae to 20°C were negatively correlated. The frequency of prolonged diapause of larvae transferred to 20°C decreased significantly after November. When larvae were submitted to different constant temperatures, the longer the daylength, the higher and faster the reactivation. These results suggest that chalcid larvae can perceive daylength through the seed coat. This phenomenon is probably related to the fact that most of the infested seeds falling in autumn are usually covered by a layer of leaf litter during the winter.
authors.affiliation: INRA-CRF, Zoologie Forestière, Ardon, 45160-Olivet, France, , , , , , FR.
authors.forename: Géraldine
authors.initials: G
authors.lastname: Roux
authors.affiliation: INRA-CRF, Zoologie Forestière, Ardon, 45160-Olivet, France, , , , , , FR.
authors.forename: Alain
authors.initials: A
authors.lastname: Roques
authors.affiliation: Laboratoire de Biométrie, Génétique et Biologie des Populations Université UMR CNRS 5558 Claude Bernard 43, bd du 11 novembre 1918, 69622 Vileurbanne Cedex, France, , , , , , FR.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Menu
keywords: Key words Prolonged diapause; Megastigmus spermotrophus; Photoperiod; Temperature; Winter diapause