Programmation de la diapause chez Gryllus campestris

Gryllus campestris has two types of development: one consists of rapid growth followed by a diapause in the penultimate larval stage, the ‘protostage’, and the other of slow growth without diapause. Experiments were designed to find the details of the programme for the two types of development.Two main temperatures, 30 and 20°C, were chosen. The sensitive period of the life cycle at 20°C was detected by subjecting insects to this temperature for a determined and increasing number of days before rearing them at 30°C during the rest of larval life. Conversely, insects were reared first at 30°C for a determined and increasing number of days and then transferred to 20°C. All these experiments led to the conclusion that the sensitive period occurs in the three last larval stages before the protostage, and that the animal is capable of following only two types of development. Experiments in which the speed of growth was slowed down by rearing insects at a cooler temperature (12°C) show that the conditions of the formation programme are not simply linked to a retardation of growth.The main effect of changing the length of days is to synchronize the arrival of all the insects at the protostage before the autumn, no matter whether the data of birth was spring or summer, or whether the number of larval stages was influenced: this explains the univoltinism of this species. Further experiments consisting of changing the length of days in the opposite direction from that of the natural seasonal evolution (increasing: 10 to 16 hr light/day instead of decreasing 16 to 10 hr) show that the programme is disturbed and subsequently the morphology of the animals is affected.To understand the genetic background of the programme a non-diapausing strain was used. It is demonstrated that selection eliminates diapause when reared at 30°C as well as normal survival when reared at 20°C. Therefore, the hypothesis of a ‘unitary system’ is here proposed for these two types of development. Hybridization of the diapausing and non-diapausing strains shows that the expression of ‘diapause’ as a response to high temperature is influenced by photoperiodism; it is dominant in short days and recessive in long days.