Manipulation of parasitoid size using the temperature-size rule: fitness consequences.

The phenotypic effects of rearing temperature on several fitness components of the koinobiont parasitoid, Aphidius colemani, were examined. Temperatures experienced during development induced a plastic linear response in the dry and fat masses of the immature stage and a non-linear response in the growth rate as well as in the size of adults. We investigated if the phenotypic morphometrical plasticity exhibited by parasitoids reared at different temperatures can induce variations in fitness-related traits in females. We did not find any difference in immature (pupal) mortality in accordance to rearing temperature. However, when examining adult longevity, we found an inverse linear relation with developmental temperature, confirming the usual rule that larger and fatter wasps live longer than smaller ones. The pattern of female fecundity was non-linear; wasps that developed at high and low temperatures were less productive. We suggest that when development is short, the accumulated reserves are not adequate to support both fecundity and survival. By manipulating adult size through changes in the rearing temperature, we showed that the usual shape of the size/fitness function is not always linear as expected. Developmental temperature induced a plasticity in energy reserves which affected the functional constraints between survival and reproduction

Alternating temperatures affect life table parameters of Phytoseiulus persimilis, Neoseiulus californicus (Acari: Phytoseiidae) and their prey Tetranychus urticae (Acari: Tetranychidae)

Increasing energy costs force glasshouse growers to switch to energy saving strategies. In the temperature integration approach, considerable daily temperature variations are allowed, which not only have an important influence on plant growth but also on the development rate of arthropods in the crop. Therefore, we examined the influence of two constant temperature regimes (15 A degrees C/15 A degrees C and 20 A degrees C/20 A degrees C) and one alternating temperature regime (20 A degrees C/5 A degrees C, with an average of 15 A degrees C) on life table parameters of Phytoseiulus persimilis and Neoseiulus californicus and their target pest, the two-spotted spider mite Tetranychus urticae at a 16:8 (L:D) h photoperiod and 65 +/- A 5 % RH. For females of both predatory mites the alternating temperature regime resulted in a 25-30 % shorter developmental time as compared to the corresponding mean constant temperature regime of 15 A degrees C/15 A degrees C. The immature development of female spider mites was prolonged for 7 days at 15 A degrees C/15 A degrees C as compared to 20 A degrees C/5 A degrees C. With a daytime temperature of 20 A degrees C, no differences in lifetime fecundity were observed between a nighttime temperature of 20 and 5 A degrees C for P. persimilis and T. urticae. The two latter species did show a higher lifetime fecundity at 20 A degrees C/5 A degrees C than at 15 A degrees C/15 A degrees C, and their daily fecundity at the alternating regime was about 30 % higher than at the corresponding mean constant temperature. P. persimilis and T. urticae showed no differences in sex ratio between the three temperature regimes, whereas the proportion of N. californicus females at 15 A degrees C/15 A degrees C (54.2 %) was significantly lower than that at 20 A degrees C/5 A degrees C (69.4 %) and 20 A degrees C/20 A degrees C (67.2 %). Intrinsic rates of increase were higher at the alternating temperature than at the corresponding mean constant temperature for both pest and predators. Our results indicate that thermal responses of the studied phytoseiid predators to alternating temperature regimes used in energy saving strategies in glasshouse crops may have consequences for their efficacy in biological control programs