Impact of size on fitness of Trichogramma evanescens (Hymenoptera : Trichogrammatidae)

Several studies have shown that a reduction in size decreases the fitness o f female parasitoids. However, it has also been suggested that the size eff ect was less important for male parasitoids. The effect of size on the fitn ess of male and female Trichogramma evanescens has been evaluated in the la boratory by producing individuals in eggs of Ephestia kuehniella (0.28 mm(3 )) and Plutella xylostella (0.13 mm(3)). Both males and females produced on P. xylostella were smaller than those produced on E. kuehniella and they h ad a reduced longevity. Small males took longer to induce receptivity in fe males and they were able to fertilize less females over their lifetime. In addition, when in competition with larger males, small males were rarely ab le to fertilize a female. Small T. evanescens females had their lifetime fe cundity reduced by two-third and this reduction was most important the firs t day of their life. These results suggest that the cost of being small is important for both males and females T. evanescens contrarily to what is as sumed in optimal sex allocation models.