Fitness consequences of low temperature storage of Aphidius ervi

In biological control programs, storage at low temperatures is used to produce large number of individuals before inundative releases. However, an exposure to low temperatures may affect the survival of exposed individuals and some life history traits such as the daily fecundity or the longevity of the survivors. This impact on life history traits is important because they will determine the growth potential of the population. To estimate the costs of different treatments of low temperature exposure, we analyzed the main instantaneous demographic parameters of the parental generation of Aphidius ervi Haliday (Hymenoptera: Braconidae: Aphidiinae) when exposed to three storage temperatures (7, 4 and 0 A degrees C), combined with two storage durations (one and two weeks) and two thermal regimes (constant and fluctuating), which represents a total of 12 treatments and a control. The average cohort generation time (Tc) decreased significantly after exposure to low temperature, particularly in fluctuating treatments. This means that development continues during storage. Cumulative fecundity and the net reproductive rate (R (0) ) decreased significantly for most of the storage treatments. This decrease was most pronounced in the constant temperature treatments. Females under fluctuating thermal regime produced a higher cumulative fecundity than those exposed to constant temperatures. Surprisingly, an exposure to 0 A degrees C over one week did not affect emergence rate and fecundity whereas all other treatments did. Storage at low temperatures may affect the efficiency of inundative releases, with the exception of storage for one week at 0 A degrees C. Moreover, cumulative fecundity and net reproductive rate (R (0) ) represent a more immediate prediction of the increase of the population after low temperature exposure than the intrinsic rate of increase (r (m) ), and reflect the qualities required in an inundative release context.