Fat and eggs: An alternative method to measure the trade-off between survival and reproduction in insect parasitoids

The cost of reproduction, a trade-off between reproduction and survival, is important in life history study. In parasitoids this trade-off is studied by measuring number of offspring and longevity. Measuring longevity, however, is a time consuming method and probably does not reflect a realistic value for survival in the field. I present an alternative method, which uses fat content as a measure for survival. Using the insect parasitoid Asobara tabida (Nees) (Hymenoptera), I show in two ways that fat content is strongly correlated to longevity. Firstly, strains with a higher fat content have a greater longevity. Secondly, fat reserves decrease linearly with age. The trade-off between reproduction and survival can be studied using this method. There is a negative correlation between the number of eggs in the ovarioles and the fat content of A. tabida females. This indicates that there is a cost of reproduction in A. tabida. The most important advantage of this method is that measuring fat content is a quick method. This method may also be applied to other insect species.