In order to understand the mechanisms where by random fluctuations in physical environmental factors may affect the population dynamics of a solitary parasitoied entomophage, the Ichneumonidae Diadromus pulchellus was reared under 2 thermoperiods found episodically in South East-France. For a given host density (5 hosts/female), the entomophagous adult population was not perturbed when their pre-imaginal or imaginal stages were subjected to an 5 degree C increase in day and night temperatures. However, male spermatogenesis, female reproductive activity and the population sex-ratio were affected, when both developmental stages were subjected to an 5 degree C increase in day/night temperatures. none